Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 1 Cisco Systems CCNA Version

Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 1

Cisco Systems CCNA Version 3 Semester 1

Module 10


Overview


Module 10: Routing Fundamentals and Subnets10.1 Routed Protocol

10.1.1 Routable and routed protocols 10.1.2 IP as a routed protocol 10.1.3 Packet propagation and switching within a router 10.1.4 Internet Protocol (IP) 10.1.5 Anatomy of an IP packet

10.2 IP Routing Protocols10.2.1 Routing overview 10.2.2 Routing versus switching 10.2.3 Routed versus routing 10.2.4 Path determination 10.2.5 Routing tables 10.2.6 Routing algorithms and metrics 10.2.7 IGP and EGP 10.2.8 Link state and distance vector 10.2.9 Routing protocols

10.3 The Mechanics of Subnetting10.3.1 Classes of network IP addresses 10.3.2 Introduction to and reason for subnetting 10.3.3 Establishing the subnet mask address 10.3.4 Applying the subnet mask 10.3.5 Subnetting Class A and B networks 10.3.6 Calculating the resident subnetwork through ANDing


10.1.1 Routable and routed protocols


• The network address is obtained by ANDing the address with the network mask.

• The reason that a network mask is used is to allow groups of sequential IP addresses to be treated as a single unit.

10.1.1 Routable and routed protocols


IP is a connectionless, unreliable, best-effort delivery

protocol.

IP determines the most efficient route for data, based on the routing protocol.


10.1.2 IP as a routed protocol

MACd MACs IPs IPd Ps Pd


10.1.3 Packet propagation and switching within a router

MACd MACs

IPs IPd

Ps Pd

• Reliable• connection-

oriented


Frame Header

MAC destinatio

n

IP Header

IP sourceMAC

source IP destinatio

n

Frame Trailer(FCS/CRC)

Segment Header

Port source

Port destinatio

n



One Complete Maximum Frame


Frame Header

MAC addresses

IP Header

IP addresses

Data…

…Data…

…Data…

FCS

…Data



Each time a packet is switched from one router interface to another the packet is de-encapsulated then encapsulated once

again.



MACd MACs

IPs IPdPs Pd

The Empty Frame is Thrown Away…

• The MAC address is changed each time the packet passes through a router.

• The Router interface is part of the attached LAN. Like a host, the router uses the MAC address to exchange topological (physical) information.



Discarded MAC addresses

Eventually these discarded Mac addresses will pile up and should be

returned to the Manufacturer for recycling.



MACd MACs IPs IPd

…and a new one is created with the Router’s Mac address.
















Routers determine the subnet network address based upon a given IP address and subnet mask by binary ANDing the two together.






MACd MACs

IPs IPd

Ps Pd





10.1.4 Internet Protocol (IP)

IP is a connectionless service. The route that the packet takes is determined by the

routers.


WAN Services

Dedicated Physical - PPP

ISDN – Private Physical Switched

VPN - Public Packet Switchedinternet

privateFrame Relay - Private Packet

Switched

Point of Demarcatio

n

The Telephone Company owns all the infrastructure

Many ways to do this.


10.1.5 Anatomy of an IP packet


IP Stuff


• Version – Indicates the version of IP currently used; four bits. If the version field is different than the IP version of the receiving device, that device will reject the packets.

• *IP header length (HLEN) – Indicates the datagram header length in 32-bit words. This is the total length of all header information, accounting for the two variable-length header fields.

• Type-of-service (TOS) – Specifies the level of importance that has been assigned by a particular upper-layer protocol, eight bits.

• Total length – Specifies the length of the entire packet in bytes, including data and header, 16 bits. To get the length of the data payload subtract the HLEN from the total length.

• Identification – Contains an integer that identifies the current datagram, 16 bits. This is the sequence number.

• *Flags – A three-bit field in which the two low-order bits control fragmentation. One bit specifies whether the packet can be fragmented, and the other specifies whether the packet is the last fragment in a series of fragmented packets.

• Fragment offset – Used to help piece together datagram fragments, 13 bits. This field allows the previous field to end on a 16-bit boundary.

• *Time-to-live (TTL) – A field that specifies the number of hops a packet may travel. This number is decreased by one as the packet travels through a router. When the counter reaches zero the packet is discarded. This prevents packets from looping endlessly.

• Protocol – indicates which upper-layer protocol, such as TCP or UDP, receives incoming packets after IP processing has been completed, eight bits.

• Header checksum – helps ensure IP header integrity, 16 bits. • IP Source• IP Destination• Options – allows IP to support various options, such as security, variable length. • *Padding – extra zeros are added to this field to ensure that the IP header is always a

multiple of 32 bits.

IP Stuff







10.2.1 Routing overview



The router compares available routing table information to select the best path.



• Routing metrics are values used in determining the advantage of one route over another. • Routing protocols use various combinations of metrics for determining the best path for data.





10.2.2 Routing versus Switching

Routing is a hierarchical organizational scheme that allows individual addresses to be grouped together; the same as area codes in the telephone network.

• Routers must maintain routing tables and make sure other routers know of changes in the network topology.

• This function is performed using a routing protocol.

• The router must use the routing table to determine where to send packets.

• The router switches the packets to the appropriate interface, adds the necessary framing information for the interface, and then transmits the frame.

016139337917IP address ? Telephone number ? Social Security

Number ?You need a subnet mask to know.


• This course focuses on Internet Protocol (IP). • Other routable or routed protocols include DecNet,

IPX/SPX, XNS and AppleTalk.• These protocols provide Layer 3 support. • Non-routable protocols do not provide Layer 3

support. • The most common non-routable protocol is

NetBEUI. • NetBEUI is a small, fast, and efficient protocol that

is limited to frame delivery within one segment.

Routable Protocols


10.2.2 Routing versus Switching 3



E1 is just another NIC on the network. The router keeps the same arp table as any of the hosts on that network.

On the WAN side, the router keeps a Routing Table.

S1S1




• Includes any network protocol that provides enough information in its network layer address for a router to forward it to the next device and thence to its destination.

• Defines the format and use of the fields within a packet.• The Internet Protocol (IP) and Novell's Internetwork Packet Exchange (IPX) are

examples of routed protocols. Other examples include DECnet, AppleTalk, Banyan VINES, and Xerox Network Systems (XNS).

RoutED


10.2.3 Routed versus routing

RoutING

1. Routing Information Protocol (RIP)2. Interior Gateway Routing Protocol (IGRP)3. Open Shortest Path First (OSPF)4. Border Gateway Protocol (BGP)5. Enhanced IGRP (EIGRP).

Distance Vector

Link State


Distance Vector

Link State

EGPIGP

IGP

IGP

IGP


10.2.4 Path determination

• Routes configured manually by the network administrator are static routes. • Routes learned by others routers using a routing protocol are dynamic

routes.



Each intersection is a router




• Routing Information Protocol (RIP) uses hop count as its only routing metric. • Interior Gateway Routing Protocol (IGRP) uses a combination of bandwidth,

delay, load, and reliability metrics to create a composite metric value.

10.2.5 Routing tables

S0


10.2.6 Routing algorithms and metrics

• Bandwidth• Delay• Load• Reliability



1. Bandwidth – The data capacity of a link. Normally, a 10-Mbps Ethernet link is preferable to a 64-kbps leased line.

2. Delay – The length of time required to move a packet along each link from source to destination. Delay depends on the bandwidth of intermediate links, the amount of data that can be temporarily stored at each router, network congestion, and physical distance.

3. Load – The amount of activity on a network resource such as a router or a link. 4. Reliability – Usually a reference to the error rate of each network link. 5. Hop count – The number of routers that a packet must travel through before

reaching its destination. Each router the data must pass through is equal to one hop. A path that has a hop count of four indicates that data traveling along that path would have to pass through four routers before reaching its final destination. If multiple paths are available to a destination, the path with the least number of hops is preferred.

6. Ticks – The delay on a data link using IBM PC clock ticks. One tick is approximately 1/18 second.

7. Cost – An arbitrary value, usually based on bandwidth, monetary expense, or other measurement, that is assigned by a network administrator.

Bad Dogs Love Routing Hairy Tom Cats



1. Optimization – Optimization describes the capability of the routing algorithm to select the best route. The route will depend on the metrics and metric weightings used in the calculation. For example, one algorithm may use both hop count and delay metrics, but may consider delay metrics as more important in the calculation.

2. Simplicity and low overhead – The simpler the algorithm, the more efficiently it will be processed by the CPU and memory in the router. This is important so that the network can scale to large proportions, such as the Internet.

3. Robustness and stability – A routing algorithm should perform correctly when confronted by unusual or unforeseen circumstances, such as hardware failures, high load conditions, and implementation errors.

4. Flexibility – A routing algorithm should quickly adapt to a variety of network changes. These changes include router availability, router memory, changes in bandwidth, and network delay.

5. Rapid convergence – Convergence is the process of agreement by all routers on available routes. When a network event causes changes in router availability, updates are needed to reestablish network connectivity. Routing algorithms that converge slowly can cause data to be undeliverable.


10.2.7 IGP and EGP

Interior Gateway Protocols

Exterior Gateway Protocols

(RIP) and (RIPv2) (IGRP) (EIGRP) (OSPF) (IS-IS)


10.2.8 Link state and distance vector IGPs can be further categorized as either:1. Distance-Vector protocols - RIP IGRP EIGRP

• Routing by rumor2. Link-State protocols.

Link-state advertisements are caused by…

topology changes link-state refresh packets

1. Distance-Vector protocols “Psst! Hey neighbor, remember who I know about?”

2. Link-State protocols. “Listen up everybody, there’s a change to the networks that I’m connected to.”







10.3.1 Classes of network IP addresses

EG: An IP address 172.32.65.13 and a default subnet mask, the host belongs to the 172.32.0.0 network.


10.3.2 Introduction to and reason for subnetting

The benefits of Subnetting1. smaller broadcast domains 2. low-level security provided 3. increased address flexibility

EG: In a class C network a subnet mask of 255.255.255.224 will create 6 useable subnets each with 32 useable hosts.



Host bits are reassigned as network bits.

• Host bits of the network address are all equal to 0.

• Host bits of the broadcast address are all equal to 1.




10.3.3 Establishing the subnet mask address



Assume Class C subnetting





Magic Numbers


10.3.4 Applying the subnet mask

Assumes subnet mask of 255.255.255.224 resulting

in a magic number = 32


10.3.4 Applying the subnet mask

Magic Numbers


10.3.5 Subnetting Class A and B networks

16 bits are available for Class B host IP addresses using the default subnet mask.

If you applied the subnet mask 255.255.255.0 to a Class B network it would give you 254

useable subnets and 254 useable hosts/subnet.

Applying the subnet mask 255.255.255.240 (/28) to a Class B network will give 4094 useable

subnets and 14 useable hosts/subnet.



To borrow 20 bits you would use subnet mask 255.255.255.240 = /28








10.3.6 Calculating the resident subnetwork through ANDing


10.3.6 Calculating the resident subnetwork through ANDing



FIN

Documents

Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 1 Cisco Systems CCNA Version