CCNA Presentation

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Data Networks

Sharing data through the use of floppy disks is not an efficient or cost-effective manner in which to operate businesses.

Businesses needed a solution that would successfully address the following three problems: • How to avoid duplication of equipment and resources • How to communicate efficiently • How to set up and manage a network

Businesses realized that networking technology could increase productivity while saving money.

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Networking Devices

Equipment that connects directly to a network segment is referred to as a device.

These devices are broken up into two classifications. • end-user devices• network devices

End-user devices include computers, printers, scanners, and other devices that provide services directly to the user.

Network devices include all the devices that connect the end-user devices together to allow them to communicate.

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Network Interface Card

A network interface card (NIC) is a printed circuit board that provides network communication capabilities to and from a personal computer. Also called a LAN adapter.

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Repeater

A repeater is a network device used to regenerate a signal. Repeaters regenerate analog or digital signals distorted by transmission loss due to attenuation. A repeater does not perform intelligent routing.

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HubHubs concentrate connections. In other words, they take a group of hosts and allow the network to see them as a single unit.

This is done passively, without any other effect on the data transmission.

Active hubs not only concentrate hosts, but they also regenerate signals.

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Bridge

Bridges convert network transmission data formats as well as perform basic data transmission management. Bridges, as the name implies, provide connections between LANs. Not only do bridges connect LANs, but they also perform a check on the data to determine whether it should cross the bridge or not. This makes each part of the network more efficient.

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Workgroup Switch

Workgroup switches add more intelligence to data transfer management.

Switches can determine whether data should remain on a LAN or not, and they can transfer the data to the connection that needs that data.

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RouterRouters have all capabilities of the previous devices. Routers can regenerate signals, concentrate multiple connections, convert data transmission formats, and manage data transfers.They can also connect to a WAN, which allows them to connect LANs that are separated by great distances.

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LANs, MANs, & WANs

One early solution was the creation of local-area network (LAN) standards which provided an open set of guidelines for creating network hardware and software, making equipment from different companies compatible.

What was needed was a way for information to move efficiently and quickly, not only within a company, but also from one business to another.

The solution was the creation of metropolitan-area networks (MANs) and wide-area networks (WANs).

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Examples of Data Networks

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LANs

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Wireless LAN Organizations and Standards

In cabled networks, IEEE is the prime issuer of standards for wireless networks. The standards have been created within the framework of the regulations created by the Federal Communications Commission (FCC).

A key technology contained within the 802.11 standard is Direct Sequence Spread Spectrum (DSSS).

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WANs

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Virtual Private NetworkA VPN is a private network that is constructed within a public network infrastructure such as the global Internet. Using VPN, a telecommuter can access the network of the company headquarters through the Internet by building a secure tunnel between the telecommuter’s PC and a VPN router in the headquarters.

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Why do we need the OSI Model?

To address the problem of networks increasing in size and in number, the International Organization for Standardization (ISO) researched many network schemes and recognized that there was a need to create a network model that would help network builders implement networks that could communicate and work together and therefore, released the OSI reference model in 1984.

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Don’t Get Confused.

ISO - International Organization for Standardization

OSI - Open System Interconnection

IOS - Internetwork Operating System

The ISO created the OSI to make the IOS more efficient. The “ISO” acronym is correct as shown.

To avoid confusion, some people say “International Standard Organization.”

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The OSI Reference Model

7 Application6 Presentation5 Session4 Transport3 Network2 Data Link1 Physical

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Layer 7 - The Application Layer


This layer deal with networking applications.

Examples: Email Web browsers

PDU - User Data

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Layer 6 - The Presentation Layer


This layer is responsible for presenting the data in the required format which may include: Encryption Compression

PDU - Formatted Data

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Layer 5 - The Session Layer


This layer establishes, manages, and terminates sessions between two communicating hosts.

Example: Client Software

( Used for logging in)

PDU - Formatted Data

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Layer 4 - The Transport Layer


This layer breaks up the data from the sending host and then reassembles it in the receiver.

It also is used to insure reliable data transport across the network.

PDU - Segments

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Layer 3 - The Network Layer


Sometimes referred to as the “Cisco Layer”.

Makes “Best Path Determination” decisions based on logical addresses (usually IP addresses).

PDU - Packets

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Layer 2 - The Data Link Layer


This layer provides reliable transit of data across a physical link.

Makes decisions based on physical addresses (usually MAC addresses).

PDU - Frames

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Layer 1 - The Physical Layer


This is the physical media through which the data, represented as electronic signals, is sent from the source host to the destination host.

Examples: CAT5 (what we have) Coaxial (like cable TV) Fiber optic

PDU - Bits

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Why Another Model?Although the OSI reference model is universally recognized, the historical and technical open standard of the Internet is Transmission Control Protocol / Internet Protocol (TCP/IP).

The TCP/IP reference model and the TCP/IP protocol stack make data communication possible between any two computers, anywhere in the world, at nearly the speed of light.

The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any conditions, even a nuclear war.

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Don’t Confuse the Models

Application

TransportInternet

Network Access


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2 ModelsSide-By-Side

Application

TransportInternet

Network Access


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The Application LayerThe application layer of the TCP/IP model handles high-level protocols, issues of representation, encoding, and dialog control.

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The transport layer provides transport services from the source host to the destination host. It constitutes a logical connection between these endpoints of the network. Transport protocols segment and reassemble upper-layer applications into the same data stream between endpoints. The transport layer data stream provides end-to-end transport services.

The Transport Layer

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The Internet LayerThe purpose of the Internet layer is to select the best path through the network for packets to travel. The main protocol that functions at this layer is the Internet Protocol (IP). Best path determination and packet switching occur at this layer.

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The Network Access LayerThe network access layer is also called the host-to-network layer. It the layer that is concerned with all of the issues that an IP packet requires to actually make a physical link to the network media. It includes LAN and WAN details, and all the details contained in the OSI physical and data-link layers. NOTE: ARP & RARP work at both the Internet and Network Access Layers.

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Comparing TCP/IP & OSI Models

NOTE: TCP/IP transport layer using UDP does not always guarantee reliable delivery of packets as the transport layer in the OSI model does.

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Introduction to the Transport Layer

The primary duties of the transport layer, Layer 4 of the OSI model, are to transport and regulate the flow of information from the source to the destination, reliably and accurately.

End-to-end control and reliability are provided by sliding windows, sequencing numbers, and acknowledgments.

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More on The Transport Layer

The transport layer provides transport services from the source host to the destination host.

It establishes a logical connection between the endpoints of the network.• Transport services include the following basic services: • Segmentation of upper-layer application data • Establishment of end-to-end operations • Transport of segments from one end host to another

end host • Flow control provided by sliding windows • Reliability provided by sequence numbers and

acknowledgments

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Flow ControlAs the transport layer sends data segments, it tries to ensure that data is not lost. A receiving host that is unable to process data as quickly as it arrives could be a cause of data loss.

Flow control avoids the problem of a transmitting host overflowing the buffers in the receiving host.

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TCP

Transmission Control Protocol (TCP) is a connection-oriented Layer 4 protocol that provides reliable full-duplex data transmission.

TCP is part of the TCP/IP protocol stack. In a connection-oriented environment, a connection is established between both ends before the transfer of information can begin. TCP is responsible for breaking messages into segments, reassembling them at the destination station, resending anything that is not received, and reassembling messages from the segments.TCP supplies a virtual circuit between end-user applications.

The protocols that use TCP include: • FTP (File Transfer Protocol) • HTTP (Hypertext Transfer Protocol) • SMTP (Simple Mail Transfer Protocol) • Telnet

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TCP Segment Format

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UDP

User Datagram Protocol (UDP) is the connectionless transport protocol in the TCP/IP protocol stack.

UDP is a simple protocol that exchanges datagrams, without acknowledgments or guaranteed delivery. Error processing and retransmission must be handled by higher layer protocols.

UDP uses no windowing or acknowledgments so reliability, if needed, is provided by application layer protocols. UDP is designed for applications that do not need to put sequences of segments together.

The protocols that use UDP include: • TFTP (Trivial File Transfer Protocol) • SNMP (Simple Network Management Protocol) • DHCP (Dynamic Host Control Protocol) • DNS (Domain Name System)

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UDP Segment Format

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Well Known Port Numbers

The following port numbers should be memorized:NOTE: The curriculum forgot to mention one of the most important port numbers. Port 80 is used for HTTP or WWW protocols. (Essentially access to the internet.)

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Network and Host Addressing

Using the IP address of the destination network, a router can deliver a packet to the correct network.

When the packet arrives at a router connected to the destination network, the router uses the IP address to locate the particular computer connected to that network.

Accordingly, every IP address has two parts.

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Identifying Address Classes

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Address Class PrefixesTo accommodate different size networks and aid in classifying these networks, IP addresses are divided into groups called classes.This is classful addressing.

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Network and Host Division

Each complete 32-bit IP address is broken down into a network part and a host part. A bit or bit sequence at the start of each address determines the class of the address. There are 5 IP address classes.

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Class A Addresses

The Class A address was designed to support extremely large networks, with more than 16 million host addresses available. Class A IP addresses use only the first octet to indicate the network address. The remaining three octets provide for host addresses.

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Class B Addresses

The Class B address was designed to support the needs of moderate to large-sized networks.A Class B IP address uses the first two of the four octets to indicate the network address. The other two octets specify host addresses.

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Class C Addresses

The Class C address space is the most commonly used of the original address classes.This address space was intended to support small networks with a maximum of 254 hosts.

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Class D Addresses

The Class D address class was created to enable multicasting in an IP address. A multicast address is a unique network address that directs packets with that destination address to predefined groups of IP addresses. Therefore, a single station can simultaneously transmit a single stream of data to multiple recipients.

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Class E Addresses

A Class E address has been defined. However, the Internet Engineering Task Force (IETF) reserves these addresses for its own research. Therefore, no Class E addresses have been released for use in the Internet.

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IP Address Ranges

The graphic below shows the IP address range of the first octet both in decimal and binary for each IP address class.

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IPv4

As early as 1992, the Internet Engineering Task Force (IETF) identified two specific concerns: Exhaustion of the remaining, unassigned IPv4 network addresses and the increase in the size of Internet routing tables.

Over the past two decades, numerous extensions to IPv4 have been developed. Two of the more important of these are subnet masks and classless interdomain routing (CIDR).

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Network Address

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Broadcast Address

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Network/Broadcast Addressesat the Binary Level

An IP address that has binary 0s in all host bit positions is reserved for the network address, which identifies the network. An IP address that has binary 1s in all host bit positions is reserved for the broadcast address, which is used to send data to all hosts on the network. Here are some examples:

Class Network Address Broadcast Address

A 100.0.0.0 100.255.255.255

B 150.75.0.0 150.75.255.255

C 200.100.50.0 200.100.50.255

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Public IP Addresses

Unique addresses are required for each device on a network.

Originally, an organization known as the Internet Network Information Center (InterNIC) handled this procedure.

InterNIC no longer exists and has been succeeded by the Internet Assigned Numbers Authority (IANA).

No two machines that connect to a public network can have the same IP address because public IP addresses are global and standardized.

All machines connected to the Internet agree to conform to the system.

Public IP addresses must be obtained from an Internet service provider (ISP) or a registry at some expense.

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Private IP Addresses

Private IP addresses are another solution to the problem of the impending exhaustion of public IP addresses.As mentioned, public networks require hosts to have unique IP addresses.

However, private networks that are not connected to the Internet may use any host addresses, as long as each host within the private network is unique.

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Introduction to Subnetting

Subnetting a network means to use the subnet mask to divide the network and break a large network up into smaller, more efficient and manageable segments, or subnets.

With subnetting, the network is not limited to the default Class A, B, or C network masks and there is more flexibility in the network design.

Subnet addresses include the network portion, plus a subnet field and a host field.The ability to decide how to divide the original host portion into the new subnet and host fields provides addressing flexibility for the network administrator.

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The 32-Bit Binary IP Address

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Numbers That Show Up In Subnet Masks (Memorize Them!)

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Addressing with Subnetworks

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Static Assignment of an IP Address

Static assignment works best on small networks.

The administrator manually assigns and tracks IP addresses for each computer, printer, or server on the intranet.

Network printers, application servers, and routers should be assigned static IP addresses.

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SIEMENSNIXDORF

SIEMENSNIXDORF

Host A

Host BIP Address: 128.0.10.4HW Address: 080020021545

ARP Reply

ARP Request - Broadcast to all hosts„What is the hardware address for IP address 128.0.10.4?“

SIEMENSNIXDORF

Fig. 32 How does ARP work? (TI1332EU02TI_0004 The Network Layer, 47)

ARP(Address Resolution Protocol)

66Fig. 33 The ARP command (TI1332EU02TI_0004 The Network Layer, 47)

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RARP

Reverse Address Resolution Protocol (RARP) associates a known MAC addresses with an IP addresses.

A network device, such as a diskless workstation, might know its MAC address but not its IP address. RARP allows the device to make a request to learn its IP address.Devices using RARP require that a RARP server be present on the network to answer RARP requests.

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Introduction to Routers A router is a special type of computer. It has the same basic components as a standard desktop PC. However, routers are designed to perform some very specific functions. Just as computers need operating systems to run software applications, routers need the Internetwork Operating System software (IOS) to run configuration files. These configuration files contain the instructions and parameters that control the flow of traffic in and out of the routers. The many parts of a router are shown below:

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RAMRandom Access Memory, also called dynamic RAM (DRAM)

RAM has the following characteristics and functions:

• Stores routing tables • Holds ARP cache • Holds fast-switching cache • Performs packet buffering (shared RAM) • Maintains packet-hold queues • Provides temporary memory for the configuration file of the router while the router is powered on • Loses content when router is powered down or restarted

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NVRAMNon-Volatile RAM

NVRAM has the following characteristics and functions:

• Provides storage for the startup configuration file • Retains content when router is powered down or restarted

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FlashFlash memory has the following characteristics and functions:

• Holds the operating system image (IOS) • Allows software to be updated without removing and replacing chips on the processor • Retains content when router is powered down or restarted • Can store multiple versions of IOS software

Is a type of electronically erasable, programmable ROM (EEPROM)

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ROMRead-Only Memory

ROM has the following characteristics and functions:

• Maintains instructions for power-on self test (POST) diagnostics • Stores bootstrap program and basic operating system software • Requires replacing pluggable chips on the motherboard for software upgrades

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InterfacesInterfaces have the following characteristics and functions:

• Connect router to network for frame entry and exit • Can be on the motherboard or on a separate module

Types of interfaces:

• Ethernet• Fast Ethernet• Serial• Token ring• ISDN BRI• Loopback• Console• Aux

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Internal Components of a 2600 Router

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Cisco IOSCisco technology is built around the Cisco Internetwork Operating System (IOS), which is the software that controls the routing and switching functions of internetworking devices.

A solid understanding of the IOS is essential for a network administrator.

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The Purpose of Cisco IOSAs with a computer, a router or switch cannot function without an operating system. Cisco calls its operating system the Cisco Internetwork Operating System or Cisco IOS.

It is the embedded software architecture in all of the Cisco routers and is also the operating system of the Catalyst switches.

Without an operating system, the hardware does not have any capabilities.

The Cisco IOS provides the following network services: • Basic routing and switching functions • Reliable and secure access to networked resources • Network scalability

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Router Command Line Interface

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Setup ModeSetup is not intended as the mode for entering complex protocol features in the router. The purpose of the setup mode is to permit the administrator to install a minimal configuration for a router, unable to locate a configuration from another source.

In the setup mode, default answers appear in square brackets [ ] following the question. Press the Enter key to use these defaults.

During the setup process, Ctrl-C can be pressed at any time to terminate the process. When setup is terminated using Ctrl-C, all interfaces will be administratively shutdown.

When the configuration process is completed in setup mode, the following options will be displayed:

[0] Go to the IOS command prompt without saving this config.[1] Return back to the setup without saving this config.[2] Save this configuration to nvram and exit.Enter your selection [2]:

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Operation of Cisco IOS SoftwareThe Cisco IOS devices have three distinct operating environments or modes: • ROM monitor • Boot ROM • Cisco IOS

The startup process of the router normally loads into RAM and executes one of these operating environments. The configuration register setting can be used by the system administrator to control the default start up mode for the router.

To see the IOS image and version that is running, use the show version command, which also indicates the configuration register setting.

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Step in Router Initialization

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Router User Interface ModesThe Cisco command-line interface (CLI) uses a hierarchical structure. This structure requires entry into different modes to accomplish particular tasks.

Each configuration mode is indicated with a distinctive prompt and allows only commands that are appropriate for that mode.

As a security feature the Cisco IOS software separates sessions into two access levels, user EXEC mode and privileged EXEC mode. The privileged EXEC mode is also known as enable mode.

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Overview of Router Modes

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Router Modes

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User Mode Commands

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Privileged Mode Commands

NOTE:There are many more commands available in privileged mode.

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CLI Command ModesAll command-line interface (CLI) configuration changes to a Cisco router are made from the global configuration mode. Other more specific modes are entered depending upon the configuration change that is required.

Global configuration mode commands are used in a router to apply configuration statements that affect the system as a whole.

The following command moves the router into global configuration mode

Router#configure terminal (or config t)Router(config)#

When specific configuration modes are entered, the router prompt changes to indicate the current configuration mode.

Typing exit from one of these specific configuration modes will return the router to global configuration mode. Pressing Ctrl-Z returns the router to all the way back privileged EXEC mode.

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Configuring a Router’s NameA router should be given a unique name as one of the first configuration tasks.

This task is accomplished in global configuration mode using the following commands:

Router(config)#hostname AmanTokyo(config)#

As soon as the Enter key is pressed, the prompt changes from the default host name (Router) to the newly configured host name (which is Tokyo in the example above).

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Settingthe Clockwith Help

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Message Of The Day (MOTD)A message-of-the-day (MOTD) banner can be displayed on all

connected terminals.

Enter global configuration mode by using the command config t

Enter the commandbanner motd # The message of the day goes here #.

Save changes by issuing the command copy run start

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Configuring a Console PasswordPasswords restrict access to routers. Passwords should always be configured for virtual terminal lines and the console line.

Passwords are also used to control access to privileged EXEC mode so that only authorized users may make changes to the configuration file.

The following commands are used to set an optional but recommended password on the console line:

Router(config)#line console 0Router(config-line)#password <password>Router(config-line)#login

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Configuring a Modem PasswordIf configuring a router via a modem you are most likely connected to the aux port.

The method for configuring the aux port is very similar to configuring the console port.

Router(config)#line aux 0Router(config-line)#password <password>Router(config-line)#login

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Configuring InterfacesAn interface needs an IP Address and a Subnet Mask to be configured. All interfaces are “shutdown” by default. The DCE end of a serial interface needs a clock rate.

Router#config tRouter(config)#interface serial 0/1Router(config-if)#ip address 200.100.50.75 255.255.255.240Router(config-if)#clock rate 56000 (required for serial DCE only) Router(config-if)#no shutdownRouter(config-if)#exitRouter(config)#int f0/0 Router(config-if)#ip address 150.100.50.25 255.255.255.0Router(config-if)#no shutdownRouter(config-if)#exitRouter(config)#exitRouter#

On older routers, Serial 0/1 would be just Serial 1 and f0/0 would be e0.s = serial e = Ethernet f = fast Ethernet

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Configuring a Telnet Password

A password must be set on one or more of the virtual terminal (VTY) lines for users to gain remote access to the router using Telnet.

Typically Cisco routers support five VTY lines numbered 0 through 4.

The following commands are used to set the same password on all of the VTY lines:

Router(config)#line vty 0 4Router(config-line)#password <password>Router(config-line)#login

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Examining the show Commands

There are many show commands that can be used to examine the contents of files in the router and for troubleshooting. In both privileged EXEC and user EXEC modes, the command show ? provides a list of available show commands. The list is considerably longer in privileged EXEC mode than it is in user EXEC mode.

show interfaces – Displays all the statistics for all the interfaces on the router. show int s0/1 – Displays statistics for interface Serial 0/1show controllers serial – Displays information-specific to the interface hardware show clock – Shows the time set in the router show hosts – Displays a cached list of host names and addresses show users – Displays all users who are connected to the router show history – Displays a history of commands that have been entered show flash – Displays info about flash memory and what IOS files are stored there show version – Displays info about the router and the IOS that is running in RAM show ARP – Displays the ARP table of the router show start – Displays the saved configuration located in NVRAM show run – Displays the configuration currently running in RAM show protocol – Displays the global and interface specific status of any configured

Layer 3 protocols

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The copy run tftp Command

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The copy tftp run Command

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Anatomy of an IP PacketIP packets consist of the data from upper layers plus an IP header. The IP header consists of the following:

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Introducing RoutingRouting is the process that a router uses to forward packets toward the destination network. A router makes decisions based upon the destination IP address of a packet. All devices along the way use the destination IP address to point the packet in the correct direction so that the packet eventually arrives at its destination. In order to make the correct decisions, routers must learn the direction to remote networks.

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Configuring Static Routes by Specifying Outgoing Interfaces

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Configuring Static Routes by Specifying Next-Hop Addresses

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Administrative DistanceThe administrative distance is an optional parameter that gives a measure of the reliability of the route. The range of an AD is 0-255 where smaller numbers are more desireable.

The default administrative distance when using next-hop address is 1, while the default administrative distance when using the outgoing interface is 0. You can statically assign an AD as follows:

Router(config)#ip route 172.16.3.0 255.255.255.0 172.16.4.1 130

Sometimes static routes are used for backup purposes. A static route can be configured on a router that will only be used when the dynamically learned route has failed. To use a static route in this manner, simply set the administrative distance higher than that of the dynamic routing protocol being used.

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Configuring Default RoutesDefault routes are used to route packets with destinations that do not match any of the other routes in the routing table.

A default route is actually a special static route that uses this format:

ip route 0.0.0.0 0.0.0.0 [next-hop-address | outgoing interface]

This is sometimes referred to as a “Quad-Zero” route.

Example using next hop address:

Router(config)#ip route 0.0.0.0 0.0.0.0 172.16.4.1

Example using the exit interface:

Router(config)#ip route 0.0.0.0 0.0.0.0 s0/0

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Verifying StaticRoute Configuration

After static routes are configured it is important to verify that they are present in the routing table and that routing is working as expected.

The command show running-config is used to view the active configuration in RAM to verify that the static route was entered correctly.

The show ip route command is used to make sure that the static route is present in the routing table.

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Trouble Shooting StaticRoute Configuration

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Routing Protocols

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Routed Protocols

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Categories of Routing Protocols

Most routing algorithms can be classified into one of two categories:

• distance vector • link-state

The distance vector routing approach determines the direction (vector) and distance to any link in the internetwork.

The link-state approach, also called shortest path first, recreates the exact topology of the entire internetwork.

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Distance VectorRouting Concepts

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RIPv1

Distance Vector Routing Protocol,classful

Distribution of Routing Tables via broadcast to adjacent routers

Only one kind of metric:Number of Hops

Connections with differentbandwidth can not be weighted

Routing loops can occur-> bad convergence in case of a failure

Count to infinity problem(infinity = 16)

Maximum network size is limitedby the number of hops

Fig. 59 Properties of R

IPv1 (TI1332E

U02TI_0004 The N

etwork Layer,

81)

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RIP Characteristics

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Router ConfigurationThe router command starts a routing process.

The network command is required because it enables the routing process to determine which interfaces participate in the sending and receiving of routing updates.

An example of a routing configuration is:

GAD(config)#router ripGAD(config-router)#network 172.16.0.0

The network numbers are based on the network class addresses, not subnet addresses or individual host addresses.

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Configuring RIP Example

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Verifying RIP Configuration

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The debug ip rip CommandMost of the RIP configuration errors involve an incorrect network statement, discontiguous subnets, or split horizons. One highly effective command for finding RIP update issues is the debug ip rip command. The debug ip rip command displays RIP routing updates as they are sent and received.

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Problem: Routing LoopsRouting loops can occur when inconsistent routing tables are not updated due to slow convergence in a changing network.

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Problem: Counting to Infinity

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Solution: Define a Maximum

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Solution: Split Horizon

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Route PoisoningRoute poisoning is used by various distance vector protocols in order to overcome large routing loops and offer explicit information when a subnet or network is not accessible. This is usually accomplished by setting the hop count to one more than the maximum.

OSPF (Open Shortest Path First) Protocol

© 2003, Cisco Systems, Inc. All rights reserved. 123

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OSPF is a Link-State Routing Protocols

–Link-state (LS) routers recognize much more information about the network than their distance-vector counterparts,Consequently LS routers tend to make more accurate decisions.

–Link-state routers keep track of the following:• Their neighbours• All routers within the same area• Best paths toward a destination

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Link-State Data Structures

–Neighbor table: • Also known as the adjacency database

(list of recognized neighbors)

–Topology table: • Typically referred to as LSDB

(routers and links in the area or network) • All routers within an area have an identical LSDB

–Routing table:• Commonly named a forwarding database

(list of best paths to destinations)

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OSPF vs. RIPRIP is limited to 15 hops, it converges slowly, and it sometimes chooses slow routes because it ignores critical factors such as bandwidth in route determination. OSPF overcomes these limitations and proves to be a robust and scalable routing protocol suitable for the networks of today.

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OSPF Areas

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Area Terminology

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LS Data Structures: Adjacency Database

– Routers discover neighbors by exchanging hello packets.

– Routers declare neighbors to be up after checking certain parameters or options in the hello packet.

– Point-to-point WAN links:• Both neighbors become fully adjacent.

– LAN links:• Neighbors form an adjacency with the DR and BDR.• Maintain two-way state with the other routers (DROTHERs).

– Routing updates and topology information are only passed between adjacent routers.

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OSPF Adjacencies

Routers build logical adjacencies between each other using the Hello Protocol. Once an adjacency is formed:• LS database packets are exchanged to synchronize each other’s LS databases.• LSAs are flooded reliably throughout the area or network using these adjacencies.

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Open Shortest Path First Calculation

•Routers find the best paths to destinations by applying Dijkstra’s SPF algorithm to the link-state database as follows:– Every router in an area has the identical

link-state database.– Each router in the area places itself into

the root of the tree that is built.– The best path is calculated with respect to the

lowest total cost of links to a specific destination.– Best routes are put into the forwarding database.

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show ip protocol

show ip route

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show ip ospf neighbor detail

show ip ospf database

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OverviewEnhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco-proprietary routing protocol based on Interior Gateway Routing Protocol (IGRP).

Unlike IGRP, which is a classful routing protocol, EIGRP supports CIDR and VLSM.

Compared to IGRP, EIGRP boasts faster convergence times, improved scalability, and superior handling of routing loops.

Furthermore, EIGRP can replace Novell Routing Information Protocol (RIP) and AppleTalk Routing Table Maintenance Protocol (RTMP), serving both IPX and AppleTalk networks with powerful efficiency.

EIGRP is often described as a hybrid routing protocol, offering the best of distance vector and link-state algorithms.

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EIGRP Concepts & TerminologyEIGRP routers keep route and topology information readily available in RAM, so they can react quickly to changes.

Like OSPF, EIGRP saves this information in several tables and databases.

EIGRP saves routes that are learned in specific ways.

Routes are given a particular status and can be tagged to provide additional useful information.

EIGRP maintains three tables:• Neighbor table • Topology table • Routing table

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Neighbor Table

The neighbor table is the most important table in EIGRP.

Each EIGRP router maintains a neighbor table that lists adjacent routers. This table is comparable to the adjacency database used by OSPF. There is a neighbor table for each protocol that EIGRP supports.

When a neighbor sends a hello packet, it advertises a hold time. The hold time is the amount of time a router treats a neighbor as reachable and operational. In other words, if a hello packet is not heard within the hold time, then the hold time expires.

When the hold time expires, the Diffusing Update Algorithm (DUAL), which is the EIGRP distance vector algorithm, is informed of the topology change and must recalculate the new topology.

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Topology TableThe topology table is made up of all the EIGRP routing tables in the autonomous system.

DUAL takes the information supplied in the neighbor table and the topology table and calculates the lowest cost routes to each destination. By tracking this information, EIGRP routers can identify and switch to alternate routes quickly.

The information that the router learns from the DUAL is used to determine the successor route, which is the term used to identify the primary or best route. A copy is also placed in the topology table.

Every EIGRP router maintains a topology table for each configured network protocol. All learned routes to a destination are maintained in the topology table.

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Routing TableThe EIGRP routing table holds the best routes to a destination. This information is retrieved from the topology table. Each EIGRP router maintains a routing table for each network protocol.

A successor is a route selected as the primary route to use to reach a destination.DUAL identifies this route from the information contained in the neighbor and topology tables and places it in the routing table.

There can be up to four successor routes for any particular route. These can be of equal or unequal cost and are identified as the best loop-free paths to a given destination.

A copy of the successor routes is also placed in the topology table.

A feasible successor (FS) is a backup route.These routes are identified at the same time the successors are identified, but they are only kept in the topology table. Multiple feasible successors for a destination can be retained in the topology table although it is not mandatory.

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EIGRP Data StructureLike OSPF, EIGRP relies on different types of packets to maintain its various tables and establish complex relationships with neighbor routers. The five EIGRP packet types are: • Hello • Acknowledgment • Update • Query • Reply

EIGRP relies on hello packets to discover, verify, and rediscover neighbor routers.

Rediscovery occurs if EIGRP routers do not receive hellos from each other for a hold time interval but then re-establish communication.

EIGRP routers send hellos at a fixed but configurable interval, called the hello interval. The default hello interval depends on the bandwidth of the interface.

On IP networks, EIGRP routers send hellos to the multicast IP address 224.0.0.10.

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Configuring EIGRP

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Configuring EIGRP SummarizationEIGRP automatically summarizes routes at the classful boundary.

This is the boundary where the network address ends, as defined by class-based addressing.

This means that even though RTC is connected only to the subnet 2.1.1.0, it will advertise that it is connected to the entire Class A network, 2.0.0.0.

In most cases auto summarization is beneficial because it keeps routing tables as compact as possible.

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Configuring EIGRP no-summaryHowever, automatic summarization may not be the preferred option in certain instances. To turn off auto-summarization, use the following command: router(config-router)#no auto-summary

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show ip eigrp neighbors

show ip eigrp interfaces

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show ip eigrp topology

show ip eigrp topology[active | pending | successors]

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show ip eigrp topologyall-links

show ip eigrp traffic

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What are ACLs?ACLs are lists of conditions that are applied to traffic traveling across a router's interface. These lists tell the router what types of packets to accept or deny. Acceptance and denial can be based on specified conditions.

ACLs can be created for all routed network protocols, such as Internet Protocol (IP) and Internetwork Packet Exchange (IPX).

ACLs can be configured at the router to control access to a network or subnet.

Some ACL decision points are source and destination addresses, protocols, and upper-layer port numbers.

ACLs must be defined on a per-protocol, per direction, or per port basis.

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Reasons to Create ACLsThe following are some of the primary reasons to create ACLs:

• Limit network traffic and increase network performance. • Provide traffic flow control. • Provide a basic level of security for network access. • Decide which types of traffic are forwarded or blocked at the router interfaces. For example: Permit e-mail traffic to

be routed, but block all telnet traffic.

Allow an administrator to control what areas a client can access on a network.

If ACLs are not configured on the router, all packets passing through the router will be allowed onto all parts of the network.

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Creating ACLsACLs are created in the global configuration mode. There are many different types of ACLs including standard, extended, IPX, AppleTalk, and others. When configuring ACLs on a router, each ACL must be uniquely identified by assigning a number to it. This number identifies the type of access list created and must fall within the specific range of numbers that is valid for that type of list.

Since IP is by far the most popular routed protocol, addition ACL numbers have been added to newer router IOSs. Standard IP: 1300-1999Extended IP: 2000-2699

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The access-list command

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The ip access-group command

{ in | out }

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ACL Example

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Basic Rules for ACLsThese basic rules should be followed when creating and applying access lists:

• One access list per protocol per direction. • Standard IP access lists should be applied closest to the destination. • Extended IP access lists should be applied closest to the source. • Use the inbound or outbound interface reference as if looking at the port from inside the router. • Statements are processed sequentially from the top of list to the bottom until a match is found, if no match is found then the packet is denied. • There is an implicit deny at the end of all access lists. This will not appear in the configuration listing. • Access list entries should filter in the order from specific to general. Specific hosts should be denied first, and groups or general filters should come last. • Never work with an access list that is actively applied. • New lines are always added to the end of the access list. • A no access-list x command will remove the whole list. It is not possible to selectively add and remove lines with numbered ACLs. • Outbound filters do not affect traffic originating from the local router.

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Wildcard Mask Examples5 Examples follow that demonstrate how a wildcard mask can be used to permit or deny certain IP addresses, or IP address ranges.

While subnet masks start with binary 1s and end with binary 0s, wildcard masks are the reverse meaning they typically start with binary 0s and end with binary 1s.

In the examples that follow Cisco has chosen to represent the binary 1s in the wilcard masks with Xs to focus on the specific bits being shown in each example.

You will see that while subnet masks were ANDed with ip addresses, wildcard masks are ORed with IP addresses.

.

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The any and host Keywords

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Verifying ACLsThere are many show commands that will verify the content and placement of ACLs on the router.

The show ip interface command displays IP interface information and indicates whether any ACLs are set.

The show access-lists command displays the contents of all ACLs on the router.

show access-list 1 shows just access-list 1.

The show running-config command will also reveal the access lists on a router and the interface assignment information.

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Standard ACLsStandard ACLs check the source address of IP packets that are routed.

The comparison will result in either permit or deny access for an entire protocol suite, based on the network, subnet, and host addresses.

The standard version of the access-list global configuration command is used to define a standard ACL with a number in the range of 1 to 99 (also from 1300 to 1999 in recent IOS).

If there is no wildcard mask. the default mask is used, which is 0.0.0.0. (This only works with Standard ACLs and is the same thing as using host.)

The full syntax of the standard ACL command is:

Router(config)#access-list access-list-number {deny | permit} source [source-wildcard ] [log]

The no form of this command is used to remove a standard ACL. This is the syntax:Router(config)#no access-list access-list-number

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Extended ACLsExtended ACLs are used more often than standard ACLs because they provide a greater range of control. Extended ACLs check the source and destination packet addresses as well as being able to check for protocols and port numbers.

The syntax for the extended ACL statement can get very long and often will wrap in the terminal window.

The wildcards also have the option of using the host or any keywords in the command.

At the end of the extended ACL statement, additional precision is gained from a field that specifies the optional Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) port number.

Logical operations may be specified such as, equal (eq), not equal (neq), greater than (gt), and less than (lt), that the extended ACL will perform on specific protocols.

Extended ACLs use an access-list-number in the range 100 to 199 (also from 2000 to 2699 in recent IOS).

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Well Known Port Numbers

Don’t forget that WWW or HTTP is 80 and POP3 is 110.

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Extended ACL Example

This extended ACL will allow people in network 200.100.50.0 to surfing the internet, but not allow any other protocols like email, ftp, etc.

access-list 101 permit tcp 200.100.50.0 0.0.0.255 any eq 80or

access-list 101 permit tcp 200.100.50.0 0.0.0.255 any eq wwwor

access-list 101 permit tcp 200.100.50.0 0.0.0.255 any eq http

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ip access-group

The ip access-group command links an existing standard or extended ACL to an interface.

Remember that only one ACL per interface, per direction, per protocol is allowed.

The format of the command is:

Router(config-if)#ip access-group access-list-number {in | out}

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Permitting a Single HostRouter(config)# access-list 1 permit 200.100.50.23 0.0.0.0orRouter(config)# access-list 1 permit host 200.100.50.23orRouter(config)# access-list 1 permit 200.100.50.23

(The implicit “deny any” ensures that everyone else is denied.)

Router(config)# int e0Router(config-if)# ip access-group 1 inorRouter(config-if)# ip access-group 1 out

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Denying a Single HostRouter(config)# access-list 1 deny 200.100.50.23 0.0.0.0Router(config)# access-list 1 permit 0.0.0.0 255.255.255.255orRouter(config)# access-list 1 deny host 200.100.50.23Router(config)# access-list 1 permit any

(The implicit “deny any” is still present, but totally irrelevant.)


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Permitting a Single NetworkClass CRouter(config)# access-list 1 permit 200.100.50.0 0.0.0.255orClass BRouter(config)# access-list 1 permit 150.75.0.0 0.0.255.255orClass ARouter(config)# access-list 1 permit 13.0.0.0 0.255.255.255



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Denying a Single NetworkClass CRouter(config)# access-list 1 deny 200.100.50.0 0.0.0.255Router(config)# access-list 1 permit anyorClass BRouter(config)# access-list 1 deny 150.75.0.0 0.0.255.255Router(config)# access-list 1 permit anyorClass ARouter(config)# access-list 1 deny 13.0.0.0 0.255.255.255Router(config)# access-list 1 permit any


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Permitting a Class C SubnetNetwork Address/Subnet Mask: 200.100.50.0/28Desired Subnet: 3rd

Process:32-28=4 2^4 = 161st Usable Subnet address range it 200.100.50.16-312nd Usable Subnet address range it 200.100.50.32-473rd Usable Subnet address range it 200.100.50.48-63

Subnet Mask is 255.255.255.240 Inverse Mask is 0.0.0.15or subtract 200.100.50.48 from 200.100.50.63 to get 0.0.0.15

Router(config)# access-list 1 permit 200.100.50.48 0.0.0.15


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Denying a Class C SubnetNetwork Address/Subnet Mask: 192.68.72.0/27Undesired Subnet: 2nd

Process:32-27=5 2^5=321st Usable Subnet address range it 192.68.72.32-632nd Usable Subnet address range it 192.68.72.64-95


Router(config)# access-list 1 deny 192.68.72.64 0.0.0.31Router(config)# access-list 1 permit any


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Permitting a Class B SubnetNetwork Address/Subnet Mask: 150.75.0.0/24Desired Subnet: 129th

Process:Since exactly 8 bits are borrowed the 3rd octet will denote the subnet number.129th Usable Subnet address range it 150.75.129.0-255




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Denying a Class B SubnetNetwork Address/Subnet Mask: 160.88.0.0/22Undesired Subnet: 50th

Process:32-22=10 (more than 1 octet) 10-8=2 2^2=41st Usable Subnet address range it 160.88.4.0-160.88.7.2552nd Usable Subnet address range it 160.88.8.0-160.88.11.255 50 * 4 = 200 50th subnet is 160.88.200.0-160.88.203.255


Router(config)# access-list 1 deny 160.88.200.0 0.0.3.255Router(config)# access-list 1 permit any

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Permitting a Class A SubnetNetwork Address/Subnet Mask: 111.0.0.0/12Desired Subnet: 13th

Process:32-12=20 20-16=4 2^4=16 1st Usable Subnet address range is 111.16.0.0-111.31.255.25513*16=20813th Usable Subnet address range is 111.208.0.0-111.223.255.255




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Denying a Class A SubnetNetwork Address/Subnet Mask: 40.0.0.0/24Undesired Subnet: 500th

Process:Since exactly 16 bits were borrowed the 2nd and 3rd octet will denote the subnet.

1st Usable Subnet address range is 40.0.1.0-40.0.1.255255th Usable Subnet address range is 40.0.255.0-40.0.255.255256th Usable Subnet address range is 40.1.0.0-40.1.0.255300th Usable Subnet address range is 40.1.44.0-40.1.44.255500th Usable Subnet address range is 40.1.244.0-40.1.244.255

Router(config)# access-list 1 deny 40.1.244.0 0 0.0.0.255Router(config)# access-list 1 permit any

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Permit Source Network

access-list 101 permit ip 200.100.50.0 0.0.0.255 0.0.0.0 255.255.255.255

or

access-list 101 permit ip 200.100.50.0 0.0.0.255 any

Implicit deny ip any any

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Deny Source Networkaccess-list 101 deny ip 200.100.50.0 0.0.0.255

0.0.0.0 255.255.255.255access-list 101 permit ip 0.0.0.0 255.255.255.255

0.0.0.0 255.255.255.255or

access-list 101 deny ip 200.100.50.0 0.0.0.255 any access-list 101 permit ip any any

Implicit deny ip any any is present but irrelevant.

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Permit Destination Networkaccess-list 101 permit ip 0.0.0.0 255.255.255.255

200.100.50.0 0.0.0.255 or

access-list 101 permit ip any 200.100.50.0 0.0.0.255


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Deny Destination Networkaccess-list 101 deny ip 0.0.0.0 255.255.255.255

200.100.50.0 0.0.0.255 access-list 101 permit ip 0.0.0.0 255.255.255.255

0.0.0.0 255.255.255.255or

access-list 101 deny ip any 200.100.50.0 0.0.0.255access-list 101 permit ip any any

Implicit deny ip any any is present but irrelevant.

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Permit one Source Network to another Destination Network

Assume the only traffic you want is traffic from network 200.100.50.0 to network 150.75.0.0



To allow 2 way traffic between the networks add this statement:


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Deny one Source Network to another Destination Network

Assume you want to allow all traffic EXCEPT from network 200.100.50.0 to network 150.75.0.0

access-list 101 deny ip 200.100.50.0 0.0.0.255 150.75.0.0 0.0.255.255

access-list 101 permit ip any any

To deny 2 way traffic between the networks add this statement:

access-list 101 deny ip 150.75.0.0 0.0.255.255 200.100.50.0 0.0.0.255

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Deny FTPAssume you do not want anyone FTPing on the network.

access-list 101 deny tcp any any eq 21


or

access-list 101 deny tcp any any eq ftp


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Deny TelnetAssume you do not want anyone telnetting on the network.



or

access-list 101 deny tcp any any eq telnet


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Deny Web SurfingAssume you do not want anyone surfing the internet.



or

access-list 101 deny tcp any any eq www


You can also use http instead of www.

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Complicated Example #1Suppose you have the following conditions: No one from Network 200.100.50.0 is allowed to FTP anywhere Only hosts from network 150.75.0.0 may telnet to network 50.0.0.0 Subnetwork 100.100.100.0/24 is not allowed to surf the internet

access-list 101 deny tcp 200.100.50.0 0.0.0.255 any eq 21

access-list 101 permit tcp 150.75.0.0 0.0.255.255 50.0.0.0 0.255.255.255 eq 23


access-list 101 deny tcp 100.100.100.0 0.0.0.255 any eq 80


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Complicated Example #2Suppose you are the admin of network 200.100.50.0. You want to permit Email only between your network and network 150.75.0.0. You wish to place no restriction on other protocols like web surfing, ftp, telnet, etc. Email server send/receive Protocol: SMTP, port 25 User Check Email Protocol: POP3, port 110This example assumes the your Email server is at addresses 200.100.50.25



access-list 101 permit tcp 200.100.50.0 0.0.0.255200.100.50.0 0.0.0.255 eq 110

access-list 101 deny tcp any any smtpaccess-list 101 deny tcp any any pop3


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NAT Network Address

Translator

Fig. 3 NAT (TI1332EU02TI_0003 New Address Concepts, 7)

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New addressing concepts

Problems with IPv4Shortage of IPv4 addresses

Allocation of the last IPv4 addresses is forecasted for the year 2005

Address classes were replaced by usage of CIDR, but this is not sufficient

Short term solution

NAT: Network Address Translator

Long term solutionIPv6 = IPng (IP next generation)

Provides an extended address range

Fig. 2 Address shortage and possible solutions (TI1332EU02TI_0003 New Address Concepts, 5)

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NAT: Network Address Translator

NATTranslates between local addresses and public ones

Many private hosts share few global addresses

Public Network

Uses public addresses

Public addresses are globally unique

Private Network

Uses private address range (local addresses)

Local addresses may not be used externally

Fig. 4 How does NAT work? (TI1332EU02TI_0003 New Address Concepts, 9)

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NAT

To be translated

exclude

reserve pool

exclude

realm with private addresses

NAT Router

realm with public addresses

map

translate

Fig. 5 Translation mechanism (TI1332EU02TI_0003 New Address Concepts, 9)

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free NATPool

A timeout value (default 15 min) instructs NAT how long to keep an association in an idle state before returning the external IP address to the free NAT pool.

Fig. 8 How does NAT know when to return the public IP address to the pool? (TI1332EU02TI_0003 New Address Concepts, 15)

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NAT Addressing Terms• Inside Local

– The term “inside” refers to an address used for a host inside an enterprise. It is the actual IP address assigned to a host in the private enterprise network.

• Inside Global– NAT uses an inside global address to represent the

inside host as the packet is sent through the outside network, typically the Internet.

– A NAT router changes the source IP address of a packet sent by an inside host from an inside local address to an inside global address as the packet goes from the inside to the outside network.

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NAT Addressing Terms• Outside Global

– The term “outside” refers to an address used for a host outside an enterprise, the Internet.

– An outside global is the actual IP address assigned to a host that resides in the outside network, typically the Internet.

• Outside Local– NAT uses an outside local address to represent the

outside host as the packet is sent through the private enterprise network.

– A NAT router changes a packet’s destination IP address, sent from an outside global address to an inside host, as the packet goes from the outside to the inside network.

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10.47.10.10 192.50.20.5

WAN

Net A

Net B

LAN LAN192.50.20.0

10.0.0.0

Router Router

RouterRouter

Router

SA = 10.47.10.10

DA = 192.50.20.5

SA = 193.50.30.4

DA = 192.50.20.5

Router A with NATRouter B

Fig. 7 An example for NAT (TI1332EU02TI_0003 New Address Concepts, 13)

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WAN

138.76.29.7

Net A10.0.0.0/8

Router

Router

Router

SA = 10.0.0.10DA = 138.76.29.7

SA = 138.76.28.4DA =138.76.29.7

NAT withWAN interface:

138.76.28.4

SA = 138.76.29.7DA = 138.76.28.4

SA = 138.76.29.7DA = 10.0.0.10

10.0.0.10

Fig. 11 An example for NAPT (TI1332EU02TI_0003 New Address Concepts, 21)

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Types Of NAT

• There are different types of NAT that can be used, which are– Static NAT– Dynamic NAT– Overloading NAT with PAT (NAPT)

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Static NAT

• With static NAT, the NAT router simply configures a one-to-one mapping between the private address and the registered address that is used on its behalf.

195

Static NAT

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Dynamic NAT

• Like static NAT, the NAT router creates a one-to-one mapping between an inside local and inside global address and changes the IP addresses in packets as they exit and enter the inside network.

• However, the mapping of an inside local address to an inside global address happens dynamically.

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Dynamic NAT

• Dynamic NAT sets up a pool of possible inside global addresses and defines criteria for the set of inside local IP addresses whose traffic should be translated with NAT.

• The dynamic entry in the NAT table stays in there as long as traffic flows occasionally.

• If a new packet arrives, and it needs a NAT entry, but all the pooled IP addresses are in use, the router simply discards the packet.

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Static NAT


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Static NAT Configuration

• To form NAT tableRouter(config)#IP Nat inside source static [inside local source IP address] [inside global source IP address]

• Assign NAT to an Interface

Router(config)#Interface [Serial x/y]Router(config-if)#IP NAT [Inside]

• See Example


200

Dynamic NAT

• Like static NAT, the NAT router creates a one-to-one mapping between an inside local and inside global address and changes the IP addresses in packets as they exit and enter the inside network.

• However, the mapping of an inside local address to an inside global address happens dynamically.


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Dynamic NAT

• Dynamic NAT sets up a pool of possible inside global addresses and defines criteria for the set of inside local IP addresses whose traffic should be translated with NAT.

• The dynamic entry in the NAT table stays in there as long as traffic flows occasionally.

• If a new packet arrives, and it needs a NAT entry, but all the pooled IP addresses are in use, the router simply discards the packet.


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Dynamic NAT Configuration

• Specify inside addresses to be translatedRouter(config)#IP Nat inside source list [standard Access List number] pool [NAT Pool Name]

• Specify NAT pool Router(config)#IP Nat pool [NAT Pool Name] [First inside global address] [Last inside global address] netmask [subnet mask]

• Assign NAT to an Interface Router(config)#Interface [Serial x/y]Router(config-if)#IP NAT [Inside]

• See Example


203

204

Ethernet Access with Hubs

205

Ethernet Access with Bridges

206

Ethernet Access with Switches

207

Today's LAN

208

Full Duplex TransmittingFull-duplex Ethernet allows the transmission of a packet and the reception of a different packet at the same time.

This simultaneous transmission and reception requires the use of two pairs of wires in the cable and a switched connection between each node. This connection is considered point-to-point and is collision free.

The full-duplex Ethernet switch takes advantage of the two pairs of wires in the cable by creating a direct connection between the transmit (TX) at one end of the circuit and the receive (RX) at the other end.

Ethernet usually can only use 50%-60% of the available 10 Mbps of bandwidth because of collisions and latency. Full-duplex Ethernet offers 100% of the bandwidth in both directions. This produces a potential 20 Mbps throughput.

209

Why Segment LANs?

210

Collision Domains

211

Segmentation with Bridges

212

Segmentation with Routers

213

Segmentation with Switches

214

Basic Operations of a SwitchSwitching is a technology that decreases congestion in Ethernet, Token Ring, and FDDI LANs. Switching accomplishes this by reducing traffic and increasing bandwidth. LAN switches are often used to replace shared hubs and are designed to work with existing cable infrastructures. Switching equipment performs the following two basic operations:• Switching data frames • Maintaining switching operations

215

Switching Methods1. Store-and-ForwardThe entire frame is received before any forwarding takes place. Filters are applied before the frame is forwarded. Most reliable and also most latency especially when frames are large.

2. Cut-ThroughThe frame is forwarded through the switch before the entire frame is received. At a minimum the frame destination address must be read before the frame can be forwarded. This mode decreases the latency of the transmission, but also reduces error detection.

3. Fragment-FreeFragment-free switching filters out collision fragments before forwarding begins. Collision fragments are the majority of packet errors. In a properly functioning network, collision fragments must be smaller than 64 bytes. Anything > 64 bytes is a valid packet and is usually received without error.

216

Frame Transmission Modes

217

Benefits of Switching

218

How Switches and BridgesLearn Addresses

Bridges and switches learn in the following ways:

• Reading the source MAC address of each received frame or datagram

• Recording the port on which the MAC address was received.

In this way, the bridge or switch learns which addresses belong to the devices connected to each port.

219

CAMContent Addressable MemoryCAM is used in switch applications:

• To take out and process the address information from incoming data packets

• To compare the destination address with a table of addresses stored within it

The CAM stores host MAC addresses and associated port numbers. The CAM compares the received destination MAC address against the CAM table contents. If the comparison yields a match, the port is provided, and switching control forwards the packet to the correct port and address.

220

Shared vs. Dedicates BandwidthIf a hub is used, bandwidth is shared. If a switch is used, then bandwidth is dedicated. If a workstation or server is directly connected to a switch port, then the full bandwidth of the connection to the switch is available to the connected computer. If a hub is connected to a switch port, bandwidth is shared between all devices connected to the hub.

221

Microsegmentation of a Network

222

Microsegmentation

223

3 Methods of Communication

224

Switches & Broadcast DomainsWhen two switches are connected, the broadcast domain is increased.

The overall result is a reduction in available bandwidth. This happens because all devices in the broadcast domain must receive and process the broadcast frame.

Routers are Layer 3 devices. Routers do not propagate broadcasts. Routers are used to segment both collision and broadcast domains.

225

Broadcast Domain

226

227

OverviewTo design reliable, manageable, and scalable networks, a network designer must realize that each of the major components of a network has distinct design requirements.

Good network design will improve performance and also reduce the difficulties associated with network growth and evolution.

The design of larger LANs includes identifying the following:• An access layer that connects end users into the LAN • A distribution layer that provides policy-based connectivity between end-user LANs • A core layer that provides the fastest connection between the distribution points

Each of these LAN design layers requires switches that are best suited for specific tasks.

228

The Access LayerThe access layer is the entry point for user workstations and servers to the network. In a campus LAN the device used at the access layer can be a switch or a hub.

Access layer functions also include MAC layer filtering and microsegmentation. Layer 2 switches are used in the access layer.

229

Access Layer SwitchesAccess layer switches operate at Layer 2 of the OSI model

The main purpose of an access layer switch is to allow end users into the network.

An access layer switch should provide this functionality with low cost and high port density.

The following Cisco switches are commonly used at the access layer: • Catalyst 1900 series • Catalyst 2820 series • Catalyst 2950 series • Catalyst 4000 series • Catalyst 5000 series

230

The Distribution LayerThe distribution layer of the network is between the access and core layers. Networks are segmented into broadcast domains by this layer. Policies can be applied and access control lists can filter packets.

The distribution layer isolates network problems to the workgroups in which they occur. The distribution layer also prevents these problems from affecting the core layer. Switches in this layer operate at Layer 2 and Layer 3.

231

Distribution Layer SwitchesThe distribution layer switch must have high performance.

The distribution layer switch is a point at which a broadcast domain is delineated. It combines VLAN traffic and is a focal point for policy decisions about traffic flow.

For these reasons distribution layer switches operate at both Layer 2 and Layer 3 of the OSI model.

Switches in this layer are referred to as multilayer switches. These multilayer switches combine the functions of a router and a switch in one device.

The following Cisco switches are suitable for the distribution layer: • Catalyst 2926G • Catalyst 5000 family • Catalyst 6000 family

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The Core LayerThe core layer is a high-speed switching backbone.

This layer of the network design should not perform any packet manipulation. Packet manipulation, such as access list filtering, would slow down the process.

Providing a core infrastructure with redundant alternate paths gives stability to the network in the event of a single device failure. The core can be designed to use Layer 2 or Layer 3 switching. Asynchronous Transfer Mode (ATM) or Ethernet switches can be used.

233

Core Layer SwitchesThe switches in this layer can make use of a number of Layer 2 technologies. Provided that the distance between the core layer switches is not too great, the switches can use Ethernet technology.

In a network design, the core layer can be a routed, or Layer 3, core. Core layer switches are designed to provide efficient Layer 3 functionality when needed.

Factors such as need, cost, and performance should be considered before a choice is made.

The following Cisco switches are suitable for the core layer: • Catalyst 6500 series • Catalyst 8500 series • IGX 8400 series • Lightstream 1010

234

235

Physical Startup of the Catalyst SwitchSwitches are dedicated, specialized computers, which contain a CPU, RAM, and an operating system.

Switches usually have several ports for the purpose of connecting hosts, as well as specialized ports for the purpose of management.

A switch can be managed by connecting to the console port to view and make changes to the configuration.

Switches typically have no power switch to turn them on and off. They simply connect or disconnect from a power source.

Several switches from the Cisco Catalyst 2950 series are shown in graphic to the right.

236

Switch LED IndicatorsThe front panel of a switch has several lights to help monitor system activity and performance. These lights are called light-emitting diodes (LEDs). The switch has the following LEDs:

• System LED • Remote Power Supply (RPS) LED • Port Mode LED • Port Status LEDs

The System LED shows whether the system is receiving power and functioning correctly.

The RPS LED indicates whether or not the remote power supply is in use.

The Mode LEDs indicate the current state of the Mode button.

The Port Status LEDs have different meanings, depending on the current value of the Mode LED.

237

Verifying Port LEDs During Switch POSTOnce the power cable is connected, the switch initiates a series of tests called the power-on self test (POST).

POST runs automatically to verify that the switch functions correctly.

The System LED indicates the success or failure of POST.

238

Connecting a Switch to a Computer

239

Examining Help in the Switch CLIThe command-line interface (CLI) for Cisco switches is very similar to the CLI for Cisco routers.

The help command is issued by entering a question mark (?).

When this command is entered at the system prompt, a list of commands available for the current command mode is displayed.

The help command is very flexible and essentially functions the same way it does in a router CLI.

This form of help is called command syntax help, because it provides applicable keywords or arguments based on a partial command.

240

Switch Command ModesSwitches have several command modes.

The default mode is User EXEC mode, which ends in a greater-than character (>).

The commands available in User EXEC mode are limited to those that change terminal settings, perform basic tests, and display system information.

The enable command is used to change from User EXEC mode to Privileged EXEC mode, which ends in a pound-sign character (#).

The configure command allows other command modes to be accessed.

241

Show Commands in User-Exec Mode

242

Setting Switch HostnameSetting Passwords on Lines

243

244

OverviewRedundancy in a network is extremely important because redundancy allows networks to be fault tolerant.

Redundant topologies based on switches and bridges are susceptible to broadcast storms, multiple frame transmissions, and MAC address database instability.

Therefore network redundancy requires careful planning and monitoring to function properly.

The Spanning-Tree Protocol is used in switched networks to create a loop free logical topology from a physical topology that has loops.

245

Redundant Switched TopologiesNetworks with redundant paths and devices allow for more network uptime.

In the graphic, if Switch A fails, traffic can still flow from Segment 2 to Segment 1 and to the router through Switch B. If port 1 fails on Switch A then traffic can still flow through port 1 on Switch B.

Switches learn the MAC addresses of devices on their ports so that data can be properly forwarded to the destination. Switches will flood frames for unknown destinations until they learn the MAC addresses of the devices.

A redundant switched topology may cause broadcast storms, multiple frame copies, and MAC address table instability problems.

246

Broadcast StormsBroadcasts and multicasts can cause problems in a switched network. Multicasts are treated as broadcasts by the switches.

Broadcasts and multicasts frames are flooded out all ports, except the one on which the frame was received.

The switches continue to propagate broadcast traffic over and over. This is called a broadcast storm. This will continue until one of the switches is disconnected. The network will appear to be down or extremely slow.

247

Multiple Frame TransmissionsIn a redundant switched network it is possible for an end device to receive multiple frames. Assume that the MAC address of Router Y has been timed out by both switches. Also assume that Host X still has the MAC address of Router Y in its ARP cache and sends a unicast frame to Router Y. The router receives the frame because it is on the same segment as Host X. Switch A does not have the MAC address of the Router Y and will therefore flood the frame out its ports. Switch B also does not know which port Router Y is on. Switch B then floods the frame it received causing Router Y to receive multiple copies of the same frame. This is a cause of unnecessary processing in all devices.

248

MAC Database InstabilityA switch can incorrectly learn that a MAC address is on one port, when it is actually on a different port. In this example the MAC address of Router Y is not in the MAC address table of either switch. Host X sends a frame directed to Router Y. Switches A & B learn the MAC address of Host X on port 0. The frame to Router Y is flooded on port 1 of both switches. Switches A and B see this information on port 1 and incorrectly learn the MAC address of Host X on port 1. When Router Y sends a frame to Host X, Switch A and Switch B will also receive the frame and will send it out port 1. This is unnecessary, but the switches have incorrectly learned that Host X is on port 1.

249

Using Bridging Loops for Redundancy

250

Logical Loop Free TopologyCreated with STP

251

Spanning Tree Protocol - 1Ethernet bridges and switches can implement the IEEE 802.1D Spanning-Tree Protocol and use the spanning-tree algorithm to construct a loop free shortest path network.

Shortest path is based on cumulative link costs. Link costs are based on the speed of the link.

252

Spanning Tree Protocol - 2The Spanning-Tree Protocol establishes a root node, called the root bridge/switch.

The Spanning-Tree Protocol constructs a topology that has one path for reaching every network node. The resulting tree originates from the root bridge/switch.

The Spanning-Tree Protocol requires network devices to exchange messages to detect bridging loops. Links that will cause a loop are put into a blocking state.

The message that a switch sends, allowing the formation of a loop free logical topology, is called a Bridge Protocol Data Unit (BPDU).

253

Selecting the Root BridgeThe first decision that all switches in the network make, is to identify the root bridge. The position of the root bridge in a network will affect the traffic flow.

When a switch is turned on, the spanning-tree algorithm is used to identify the root bridge. BPDUs are sent out with the Bridge ID (BID).

The BID consists of a bridge priority that defaults to 32768 and the switch base MAC address.

When a switch first starts up, it assumes it is the root switch and sends BPDUs. These BPDUs contain the switch MAC address in both the root and sender BID. As a switch receives a BPDU with a lower root BID it replaces that in the BPDUs that are sent out. All bridges see these and decide that the bridge with the smallest BID value will be the root bridge.

A network administrator may want to influence the decision by setting the switch priority to a smaller value than the default.

254

BDPUsBPDUs contain enough information so that all switches can do the following:• Select a single switch that will act as the root of the spanning tree • Calculate the shortest path from itself to the root switch • Designate one of the switches as the closest one to the root, for each LAN segment. This bridge is called the “designated switch”. The designated switch handles all communication from that LAN towards the root bridge. • Each non-root switch choose one of its ports as its root port, this is the interface that gives the best path to the root switch. • Select ports that are part of the spanning tree, the designated ports. Non-designated ports are blocked.

255

Spanning Tree OperationWhen the network has stabilized, it has converged and there is one spanning tree per network. As a result, for every switched network the following elements exist:• One root bridge per network • One root port per non root bridge • One designated port per segment • Unused, non-designated ports Root ports and designated ports are used for forwarding (F) data traffic.Non-designated ports discard data traffic. Non-designated ports are called blocking (B) or discarding ports.

256

Spanning Tree Port States

257

Spanning Tree RecalculationA switched internetwork has converged when all the switch and bridge ports are in either the forwarding or blocked state.

Forwarding ports send and receive data traffic and BPDUs.

Blocked ports will only receive BPDUs.

When the network topology changes, switches and bridges recompute the Spanning Tree and cause a disruption of user traffic.

Convergence on a new spanning-tree topology using the IEEE 802.1D standard can take up to 50 seconds.

This convergence is made up of the max-age of 20 seconds, plus the listening forward delay of 15 seconds, and the learning forward delay of 15 seconds.

258

Rapid STP Designations

259

260

VLANsVLAN implementation combines Layer 2 switching and Layer 3 routing technologies to limit both collision domains and broadcast domains.

VLANs can also be used to provide security by creating the VLAN groups according to function and by using routers to communicate between VLANs.

A physical port association is used to implement VLAN assignment.

Communication between VLANs can occur only through the router.

This limits the size of the broadcast domains and uses the router to determine whether one VLAN can talk to another VLAN.

NOTE: This is the only way a switch can break up a broadcast domain!

261

Setting up VLAN Implementation

262

VLAN Communication

263

VLAN Membership Modes

• VLAN membership can either be static or dynamic.

264• All users attached to same switch port must be in the same VLAN.

Static VLANs

265

Configuring VLANs in Global Mode

Switch#configure terminal Switch(config)#vlan 3 Switch(config-vlan)#name Vlan3Switch(config-vlan)#exit Switch(config)#end

266

Configuring VLANs in VLAN Database Mode

Switch#vlan database Switch(vlan)#vlan 3

VLAN 3 added: Name: VLAN0003Switch(vlan)#exit APPLY completed.Exiting....

267

Deleting VLANs in Global Mode

Switch#configure terminal Switch(config)#no vlan 3 Switch(config)#end

268

Deleting VLANs in VLAN Database Mode

Switch#vlan database Switch(vlan)#no vlan 3

VLAN 3 deleted: Name: VLAN0003Switch(vlan)#exit APPLY completed.Exiting....

269

Assigning Access Ports to a VLAN

Switch(config)#interface gigabitethernet 1/1

• Enters interface configuration mode

Switch(config-if)#switchport mode access

• Configures the interface as an access port

Switch(config-if)#switchport access vlan 3

• Assigns the access port to a VLAN

270

Verifying the VLAN Configuration

Switch#show vlan [id | name] [vlan_num | vlan_name]

VLAN Name Status Ports---- -------------------------------- --------- -------------------------------1 default active Fa0/1, Fa0/2, Fa0/5, Fa0/7 Fa0/8, Fa0/9, Fa0/11, Fa0/12 Gi0/1, Gi0/22 VLAN0002 active51 VLAN0051 active52 VLAN0052 active… VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------1 enet 100001 1500 - - - - - 1002 10032 enet 100002 1500 - - - - - 0 051 enet 100051 1500 - - - - - 0 052 enet 100052 1500 - - - - - 0 0… Remote SPAN VLANs------------------------------------------------------------------------------Primary Secondary Type Ports------- --------- ----------------- ------------------------------------------

271

Verifying the VLAN Port Configuration

Switch#show running-config interface {fastethernet | gigabitethernet} slot/port

• Displays the running configuration of the interface

Switch#show interfaces [{fastethernet | gigabitethernet} slot/port] switchport

• Displays the switch port configuration of the interface

Switch#show mac-address-table interface interface-id [vlan vlan-id] [ | {begin | exclude | include} expression]

• Displays the MAC address table information for the specified interface in the specified VLAN

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Implementing VLAN Trunks

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN v2.0—2-272

273

VLAN Trunking

274

Importance of Native VLANs

275

– Performed with ASIC– Not intrusive to client

stations; client does not see the header

– Effective between switches, and between routers and switches

ISL Encapsulation

276

ISL and Layer 2 Encapsulation

277

Configuring ISL Trunking

Switch(config)#interface fastethernet 2/1

Switch(config-if)#switchport mode trunk

Switch(config-if)#switchport trunk encapsulation [isl|dot1q]

• Enters interface configuration mode

• Selects the encapsulation

• Configures the interface as a Layer 2 trunk

278

Verifying ISL TrunkingSwitch#show running-config interface {fastethernet | gigabitethernet} slot/port

Switch#show interfaces [fastethernet | gigabitethernet] slot/port [ switchport | trunk ]

Switch#show interfaces fastethernet 2/1 trunk

Port Mode Encapsulation Status Native VLAN Fa2/1 desirable isl trunking 1

Port VLANs allowed on trunk Fa2/1 1-1005

Port VLANs allowed and active in management domain Fa2/1 1-2,1002-1005

Port VLANs in spanning tree forwarding state and not pruned Fa2/1 1-2,1002-1005

279

802.1Q Trunking

280

Configuring 802.1Q Trunking

Switch(config)#interface fastethernet 5/8 Switch(config-if)#shutdown Switch(config-if)#switchport trunk encapsulation dot1q Switch(config-if)#switchport trunk allowed vlan 1,15,11,1002-1005 Switch(config-if)#switchport mode trunkSwitch(config-if)#switchport nonegotiate Switch(config-if)#no shutdown

281

Verifying 802.1Q TrunkingSwitch#show running-config interface {fastethernet | gigabitethernet} slot/port

Switch#show interfaces [fastethernet | gigabitethernet] slot/port [ switchport | trunk ]

Switch#show interfaces gigabitEthernet 0/1 switchportName: Gi0/1Switchport: EnabledAdministrative Mode: trunkOperational Mode: trunkAdministrative Trunking Encapsulation: dot1qOperational Trunking Encapsulation: dot1qNegotiation of Trunking: OnAccess Mode VLAN: 1 (default)Trunking Native Mode VLAN: 1 (default)Trunking VLANs Enabled: ALLPruning VLANs Enabled: 2-1001 . . .

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Implementing VLAN Trunk Protocol

© 2003, Cisco Systems, Inc. All rights reserved. BCMSN 2.0—2-282

283

– Advertises VLAN configuration information– Maintains VLAN configuration consistency throughout a

common administrative domain– Sends advertisements on trunk ports only

VTP Protocol Features

284

• Cannot create, change, or delete VLANs

• Forwards advertisements

• Synchronizes VLAN configurations

• Does not save in NVRAM

• Creates, modifies, and deletes VLANs

• Sends and forwards advertisements

• Synchronizes VLAN configurations

• Saves configuration in NVRAM

• Creates, modifies, and deletes VLANs locally only

• Forwards advertisements

• Does not synchronize VLAN configurations

• Saves configuration in NVRAM

VTP Modes

285

VTP Operation• VTP advertisements are sent as multicast frames. • VTP servers and clients are synchronized to the latest update identified

revision number.• VTP advertisements are sent every 5 minutes or when there is a change.

286

• Increases available bandwidth by reducing unnecessary flooded traffic• Example: Station A sends broadcast, and broadcast is flooded only toward

any switch with ports assigned to the red VLAN.

VTP Pruning

287

VTP Configuration Guidelines– Configure the following:

• VTP domain name • VTP mode (server mode is the default)• VTP pruning• VTP password

– Be cautious when adding a new switch into an existing domain.

– Add a new switch in a Client mode to get the last up-to-date information from the network then convert it to Server mode.

– Add all new configurations to switch in transparent mode and check your configuration well then convert it to Server mode to prevent the switch from propagating incorrect VLAN information.

288

Configuring a VTP Server

Switch(config)#vtp server

• Configures VTP server mode

Switch(config)#vtp domain domain-name

• Specifies a domain name

Switch(config)#vtp password password

• Sets a VTP password

Switch(config)#vtp pruning

• Enables VTP pruning in the domain

289

Configuring a VTP Server (Cont.)

Switch#configure terminal

Switch(config)#vtp server

Setting device to VTP SERVER mode.Switch(config)#vtp domain Lab_Network

Setting VTP domain name to Lab_NetworkSwitch(config)#end

290

Verifying the VTP ConfigurationSwitch#show vtp status

Switch#show vtp status

VTP Version : 2Configuration Revision : 247Maximum VLANs supported locally : 1005Number of existing VLANs : 33VTP Operating Mode : ClientVTP Domain Name : Lab_NetworkVTP Pruning Mode : EnabledVTP V2 Mode : DisabledVTP Traps Generation : DisabledMD5 digest : 0x45 0x52 0xB6 0xFD 0x63 0xC8 0x49 0x80Configuration last modified by 0.0.0.0 at 8-12-99 15:04:49Switch#

291

Verifying the VTP Configuration (Cont.)

Switch#show vtp counters

Switch#show vtp counters

VTP statistics:Summary advertisements received : 7Subset advertisements received : 5Request advertisements received : 0Summary advertisements transmitted : 997Subset advertisements transmitted : 13Request advertisements transmitted : 3Number of config revision errors : 0Number of config digest errors : 0Number of V1 summary errors : 0 VTP pruning statistics:Trunk Join Transmitted Join Received Summary advts received from non-pruning-capable device---------------- ---------------- ---------------- ---------------------------Fa5/8 43071 42766 5

292

293

Contents

• Remote access overview• WAN Connection Types• Defining WAN Encapsulation Protocols• Determining the WAN Type to Use• OSI Layer-2 Point-to-Point WANs

– PPP– HDLC– Frame Relay

294

Remote Access Overview

• A WAN is a data communications network covering a relatively broad geographical area.

• A network administrator designing a remote network must weight issues concerning users needs such as bandwidth and cost of the variable available technologies.

295

WAN Connection Types

296


• Leased lines– It is a pre-established WAN communications path

from the CPE, through the DCE switch, to the CPE of the remote site, allowing DTE networks to communicate at any time with no setup procedures before transmitting data.

• Circuit switching– Sets up line like a phone call. No data can transfer

before the end-to-end connection is established.

297


• Packet switching– WAN switching method that allows you to share

bandwidth with other companies to save money. As long as you are not constantly transmitting data and are instead using bursty data transfers, packet switching can save you a lot of money.

– However, if you have constant data transfers, then you will need to get a leased line.

– Frame Relay and X.25 are packet switching technologies.

298

Defining WAN Encapsulation Protocols

• Each WAN connection uses an encapsulation protocol to encapsulate traffic while it crossing the WAN link.

• The choice of the encapsulation protocol depends on the underlying WAN technology and the communicating equipment.

299

Defining WAN Encapsulation Protocols

• Typical WAN encapsulation types include the following:

– Point-to-Point Protocol (PPP)– Serial Line Internet Protocol (SLIP)– High-Level Data Link Control Protocol (HDLC)– X.25 / Link Access Procedure Balanced (LAPB)– Frame Relay– Asynchronous Transfer Mode (ATM)

300

Determining the WAN Type to Use

• Availability– Each type of service may be available in certain

geographical areas.• Bandwidth

– Determining usage over the WAN is important to evaluate the most cost-effective WAN service.

• Cost– Making a compromise between the traffic you need to

transfer and the type of service with the available cost that will suit you.

301

Determining the WAN Type to Use

• Ease of Management– Connection management includes both the

initial start-up configuration and the outgoing configuration of the normal operation.

• Application Traffic– Traffic may be as small as during a terminal

session , or very large packets as during file transfer.

302

Max. WAN Speeds for WAN Connections

WAN Type Maximum Speed

Asynchronous Dial-Up 56-64 Kbps

X.25, ISDN – BRI 128 Kbps

ISDN – PRI E1 / T1

Leased Line / Frame Relay E3 / T3

303

OSI Layer-2 Point-to-Point WANs

• WAN protocols used on Point-to-Point serial links provide the basic function of data delivery across that one link.

• The two most popular data link protocols used today are Point-to-Point Protocol (PPP) and High-Level Data Link Control (HDLC).

304

HDLC

• HDLC performs OSI Layer-2 functions.• It determines when it is appropriate to use

the physical medium.• Ensures that the correct recipient receives

and processes the data that is sent.• Determines whether the sent data was

received correctly or not (error detection).

305

HDLC

• HDLC Frame Format

• The original HDLC didn’t include any Protocol Type field, every company (including Cisco) added its own field, so it became a proprietary protocol that can be used between only Cisco routers.

306

Point-to-Point Protocol (PPP)

• PPP is a standard encapsulation protocol for the transport of different Network Layer protocols (including, but not limited to, IP).

• It has the following main functional components– Link Control Protocol (LCP) that establishes,

authenticates, and tests the data link connection.– Network Control Protocols (NCPs) that establishes

and configure different network layer protocols.

307

Point-to-Point Protocol (PPP)

• PPP discards frames that do not pass the error check.

• PPP is a standard protocol, and so it can be used with all types of routers (not Cisco Proprietary).

308

PPP LCP Features

• Authentication • Compression • Multilink PPP• Error Detection• Looped Link Detection

309

PAP Authentication

310

CHAP Authentication

311

Compression• Compression enables higher data throughput

across the link.• Different compression schemes are available:

– Predictor : checks if the data was already compressed.

– Stacker : it looks at the data stream and only sends each type of data once with information about where the type occurs and then the receiving side uses this information to reassemble the data stream.

– MPPC (Microsoft Point-to-Point Compression) : allows Cisco routers to compress data with Microsoft clients.

312

PPP Multilink

• PPP Multilink provides load balancing over dialer interfaces-including ISDN, synchronous, and asynchronous interfaces.

• This can improve throughput and reduce latency between systems by splitting packets and sending fragments over parallel circuits.

313

Error Detection

• PPP can take down a link based on the value of what is called LQM (Link Quality Monitor) as it gets the ratio of corrupted packets to the total number of sent packets, and according to a predetermined value, the link can be brought down if it is thought that its performance is beyond limits accepted.

314

Looped Link Detection

• PPP can detect looped links (that are sometimes done by Teleco companies) using what is called Magic Number.

• Every router will have a magic number, and if packets were received having the same router’s magic number, then the link is looped.

315

PPP Configuration Commands

• To enable PPP– Router(config-if)#encapsulation ppp

• To configure PAP authentication– Router(Config-if)#ppp authentication pap– Router(Config-if)#ppp pap username .. password ..

• To configure Compression– Router(Config-if)#compress [predictor|stack|mppc]

316

Frame Relay


317

Frame Relay Components

318

Frame Relay

• The switch examines the frame sent by the router that has a header containing an address called DLCI (Data Link Control Identifier) and then switches the frame based on the DLCI till it reaches the router on the other side of the network.

319

Frame Relay

• Frame Relay networks use permanent virtual circuits (PVCs) or switched virtual circuits (SVCs) but most nowadays Frame Relay networks use permanent virtual circuits (PVCs).

• The logical path between each pair of routers is called a Virtual Circuit (VC).

• VCs share the access link and the frame relay network.• Each VC is committed to a CIR (Committed Information

Rate) which is a guarantee by the provider that a particular VC gets at least this much of BW.

320

Video

PBX

Controller

PC

Router

CPEUNI

ISDN dial-up connectionordirect connection(V.35, E1, RS232)

Desktop & LAN Network access Frame RelayNetwork

Formatspacketsin frames

Port

PVC

PVC

PVC

SVC

SVC

Switch

321

LMI and Encapsulation Types• The LMI is a definition of the messages used

between the DTE and the DCE.

• The encapsulation defines the headers used by a DTE to communicate some information to the DTE on the other end of a VC.

• The switch and its connected router care about using the same LMI; the switch does not care about the encapsulation. The endpoint routers (DTEs) do care about the encapsulation.

322

LMI• The most important LMI message is the LMI

status inquiry message. Status messages perform two key functions:

– Perform a keepalive function between the DTE and DCE. If the access link has a problem, the absence of keepalive messages implies that the link is down.

– Signal whether a PVC is active or inactive. Even though each PVC is predefined, its status can change.

323

LMI

• Three LMI protocol options are available in Cisco IOS software: Cisco, ITU, and ANSI.

• Each LMI option is slightly different and therefore is incompatible with the other two.

324

LAPF• A Frame Relay-connected router encapsulates

each Layer 3 packet inside a Frame Relay header and trailer before it is sent out an access link.

• The header and trailer are defined by the Link Access Procedure Frame Bearer Services (LAPF) specification.

• The LAPF framing provides error detection with an FCS in the trailer, as well as the DLCI, DE, FECN, and BECN fields in the header.

325

LAPF• DTEs use and react to the fields specified by

these two types of encapsulation, but Frame Relay switches ignore these fields. Because the frames flow from DTE to DTE, both DTEs must agree to the encapsulation used.

• However, each VC can use a different encapsulation. In the configuration, the encapsulation created by Cisco is called cisco, and the other one is called ietf.

326

DLCI Addressing Details

• The logical path between a pair of DTEs is called a virtual circuit (VC).

• The data-link connection identifier (DLCI) identifies each individual PVC.

• When multiple VCs use the same access link, the Frame Relay switches know how to forward the frames to the correct remote sites.

The DLCI is the Frame Relay address describing a Virtual Circuit

327

B

R

R

Virtual circuit

Router

Bridge

Frame Relay switch

R

B

FR-networkDLCI=16

DLCI=32

DLCI=16 DLCI=16DLCI=21

DLCI=17

DLCI=17DLCI=32

328

DLCI Addressing Details

• The difference between layer-2 addressing and DLCI addressing is mainly because the fact that the header has a single DLCI field, not both Source and Destination DLCI fields.

329

Global DLCI Addressing• Frame Relay DLCIs are locally significant; this

means that the addresses need to be unique only on the local access link.

• Global addressing is simply a way of choosing DLCI numbers when planning a Frame Relay network so that working with DLCIs is much easier.

• Because local addressing is a fact, global addressing does not change these rules. Global addressing just makes DLCI assignment more obvious.

330

Global DLCI Addressing

331

Global DLCI Addressing

• The final key to global addressing is that the Frame Relay switches actually change the DLCI value before delivering the frame.

• The sender treats the DLCI field as a destination address, using the destination’s global DLCI in the header.

• The receiver thinks of the DLCI field as the source address, because it contains the global DLCI of the frame’s sender.

332

Layer 3 Addressing

• Cisco’s Frame Relay implementation defines three different options for assigning subnets and IP addresses on Frame Relay interfaces:– One subnet containing all Frame Relay DTEs– One subnet per VC– A hybrid of the first two options

333

One Subnet Containing All Frame Relay DTEs

• The single-subnet option is typically used when a full mesh of VCs exists.

• In a full mesh, each router has a VC to every other router, meaning that each router can send frames directly to every other router

334


335


336

One Subnet Per VC• The single-subnet-per-VC alternative, works better with a

partially meshed Frame Relay network.

337

One Subnet Per VC

338

Hybrid Terminology

• Point-to-point subinterfaces are used when a single VC is considered to be all that is in the group—for instance, between Routers A and D and between Routers A and E.

• Multipoint subinterfaces are used when more than two routers are considered to be in the same group— for instance, with Routers A, B, and C.

339

Hybrid Terminology

340

Hybrid Terminology

341

Frame Relay Address Mapping

• Mapping creates a correlation between a Layer-3 address (IP Address) and its corresponding Layer-2 address (DLCI in Frame Relay).

• It is used so that after the router receives the packet with the intended IP address could be able to handle it to the right Frame Relay switch (with the appropriate DLCI)

342

Mapping Methods

• Mapping can be done either two ways: • Dynamic Mapping

– Using the Inverse ARP that is enabled by default on Cisco routers.

• Static Mapping– Using the frame-relay map command but you

should first disable the inverse arp using the command no frame-relay inverse-arp

343

Inverse ARP Process

344

Frame Relay Configuration

345

Frame Relay Verification

346

Integrated Services Digital Network (ISDN)


347

ISDN Protocols

348

BRI & PRI B and D Channels

349

LAPD & PPP on D and B Channels

350


• LAPD is used as a data-link protocol across an ISDN D channel.

• Essentially, a router with an ISDN interface needs to send and receive signaling messages to and from the local ISDN switch to which it is connected.

• LAPD provides the data-link protocol that allows delivery of messages across that D channel to the local switch.

351


• The call setup and teardown messages themselves are defined by the Q.931 protocol. So, the local switch can receive a Q.931 call setup request from a router over the LAPD-controlled D channel, and it should react to that Q.931 message by setting up a circuit over the public network.

352


• An ISDN switch often requires some form of authentication with the device connecting to it.

• Switches use a free-form decimal value, call the service profile identifier (SPID), to perform authentication.

• In short, before any Q.931 call setup messages are accepted, the switch asks for the configured SPID values. If the values match what is configured in the switch, call setup flows are accepted.

353

PRI Encoding and Framing• ISDN PRI in North America is based on a digital

T1 circuit. T1 circuits use two different encoding schemes—Alternate Mark Inversion (AMI) and Binary 8 with Zero Substitution (B8ZS).

• The two options for framing on T1s are to use either Extended Super Frame (ESF) or the older option—Super Frame (SF). In most cases today, new T1s use ESF.

354

DDR (Dial On Demand Routing)

• You can configure DDR in several ways, including Legacy DDR and DDR dialer profiles.

• The main difference between the two is that Legacy DDR associates dial details with a physical interface, whereas DDR dialer profiles disassociate the dial configuration from a physical interface, allowing a great deal of flexibility.

355

Legacy DDR Operation

• Route packets out the interface to be dialed.• Determine the subset of the packets that

trigger the dialing process.• Dial (signal).• Determine when the connection is

terminated.

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Legacy DDR Operation

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DDR Step 1: Routing Packets Out the Interface to Be Dialed

• DDR does not dial until some traffic is directed (routed) out the dial interface.

• The router needs to route packets so that they are queued to go out the dial interface. Cisco’s design for DDR defines that the router receives some user-generated traffic and, through normal routing processes, decides to route the traffic out the interface to be dialed.

• The router (SanFrancisco) can receive a packet that must be routed out BRI0; routing the packet out BRI0 triggers the Cisco IOS software, causing the dial to occur.

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DDR Step 2: Determining the Interesting Traffic

• Packets that are worthy of causing the device to dial are called interesting packets.

• Two different methods can be used to define interesting packets. – In the first method, interesting is defined as all

packets of one or more Layer 3 protocols.– The second method allows you to define packets as

interesting if they are permitted by an access list.

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DDR Step 3: Dialing (Signaling)

• Defining the phone number to be dialed.

• The command is dialer string , where string is the phone number (used when dialing only one site).

• The dialer map command maps the different dialer numbers to the equivalent IP addresses of the routers to be dialed.

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Configuring SPIDs

• You might need to configure the Service Profile Identifier (SPID) for one or both B channels, depending on the switch’s expectations.

• When the telco switch has configured SPIDs, it might not allow the BRI line to work unless the router announces the correct SPID values to the switch. SPIDs, when used, provide a basic authentication feature.

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ISDN PRI Configuration• Configure the type of ISDN switch to which this

router is connected.• Configure the T1 or E1 encoding and framing

options (controller configuration mode).• Configure the T1 or E1 channel range for the

DS0 channels used on this PRI (controller configuration mode).

• Configure any interface settings (for example, PPP encapsulation and IP address) on the interface representing the D channel.

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PRI Configuration Commands

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ISDN Switch Types

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Configuring a T1 or E1 Controller

• Your service provider will tell you what encoding and framing to configure on the router. Also, in almost every case, you will use all 24 DS0 channels in the PRI—23 B channels and the D channel.

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DDR With Dialer Profiles

• Dialer profiles pool the physical interfaces so that the router uses any available B channel on any of the BRIs or PRIs in the pool.

• Dialer profiles configuration moves most of the DDR interface configuration to a virtual interface called a dialer interface.

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Dialer Profiles Configuration

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Dialer Profiles Configuration

With all my best wishes for you to succeed and distinguish in the

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