Chapter 3: LAN Protocols

Legacy ProtocolsA legacy protocol was widely used in the past, but are rarely implemented now. You may encounter legacy protocols on older networks.

Appletalk. Used by apple computers in the 1980s and 1990s. Modern apple networks use TCP/IP.

DLC Protocol. Used by Hewlett-Packard, often for printers. Also known as JetDirect. HP printers use TCP/IP now.

NetBEUI. Used by Microsoft until the release of Windows 2000.

IPX/SPX. Novell’s legacy protocol. Modern Novell networks use TCP/IP.

TCP/IPStands for Transmission Control Protocol/Internet Protocol.

• Core protocol of the Internet since 1983.

• In use on almost all LANs today.

• IP is an OSI Layer 3 Protocol.

• TCP is an OSI Layer 4 protocol.

• There are two IP standards–IPv4 and IPv6.

IPv4209.46.18.195

11010001.00101110.00010010.11000011

• In common use today on the Internet and LANs. Packet Header varies in size

• Uses 32-bit address as shown above in blue or 2^32

• When represented in decimal form, an IP address has four numbers, one for each byte. This notation is dotted quad and takes the form shown above in red. The decimal value of each quad is between 0 and 255.

• Certain address spaces are reserved for private and multicast networks. These addresses can not be used on the Internet, but can be used on LANs.

• Private IP address space is most commonly used on LANs. Private address space includes the following ranges.

10.0.0.0 to 10.255.255.255 Class A172.16.0.0 to 172.31.255.255 Class B192.168.0.0 to 192.168.255.255 Class C

IPv6bits 16 16 16 16 16 16 16 16 = 128

IPv6 2001:0db8:85a3:08d3:1319:8a2e:0370:7344

• In limited use today, is likely to be in common use by the end of the decade. Being tested on Internet II

• Uses a 128-bit address, represented as a 32-digit hexadecimal address. Normally written as eight groups of 4 hex digits as shown above in red.

• Will allow every network device in the world to have a unique address.

• Supported by modern operating systems.

• Different IPv6 forms of expression 1080:0000:0000:0000:0000:7435:192.168.100.1 1080:0:0:0:0:7435:192.168.100.1 1080:0:7435:192.168.100.1 1080::7435:192.168.100.1

IP Version 6 • The next generation of the IP protocol is IPv6. 2^128• 340 undecillion or 340 trillion, trillion, trillion addresses• It uses a fixed packet header size of 40 bytes so that

information always appears in the same place.

Goals of IPv6• To provide for transition from IPv4• Simplify the header fields of IP• Provide for authentication and privacy• To expand routing capabilities• To expand addressing capabilities• To expand quality of service capabilities• To improve support for options

IPv6 IP Header

Subnet Masks255.255.240.0

11111111.11111111.11110000.00000000

• Like an IPv4 address, a 32-bit number.

• Used with IPv4 addresses to logically segment networks.

• A host uses its IP address and the subnet mask to determine which addresses are on the local network and which are on remote networks.

• Traffic destined for hosts on the local network is sent directly to that host.

• Traffic destined for remote networks is sent to the router.

Network Address Translation

• Where one public IP address (one that is unique to the Internet) is shared by hosts on the private network.

• Hosts on the Internet can not initiate contact with a host on the private network.

• Hosts on the private network can initiate contact with hosts on the Internet.

• Once contact is established, bi-directional communication is possible.

Address AssignmentAddresses must be unique to the network.

o Two hosts on the Internet cannot have the same IP address.

o Two hosts on an organization’s private network cannot have the same IP address.

o Two hosts on different organizations private networks can have the same IP address.

DHCP Address Assignment

• Addresses can be assigned manually or dynamically.

• DHCP is commonly used to assign TCP/IP addresses automatically.

o Computer boots up and is assigned TCP/IP configuration via network.

o Addresses can be assigned on a first come, first serve basis from a pool or reserved on the basis of MAC address.

Dynamic Host Configuration Protocol (DHCP)Bootstrap Protocol (BOOTP)

• DHCP assigns addresses from a poll, then removes it from pool– Host sends DHCPDISCOVER message on local IP subnet

to find the DHCP server, using IP broadcast address– DHCP server response with DHCPOFFER message– Host sends DHCPREQUEST message to identify the

server to be used– Server response with DHCPACK message with the

assigned IP for client• Host sends on port 67 UDP• Server sends on port 68 UDP

• Address can be reserved for a specific MAC• DHCP Relay Agents can help cross subnets for server

Dynamic Host Configuration Protocol (DHCP)Bootstrap Protocol (BOOTP)

• Parameters a DHCP can automatically set– IP address– Subnet mask– Gateway (router) address– DNS address– WINS address– Wins client mode

• BOOTP diskless operating systems, automatically configure host during bootup on a TCP/IP network

DNS (Domain Name System)

• Used to translate friendly names such as www.emcp.com into IP Addresses such as 209.46.18.195.

• DNS is distributed. No single server hosts all DNS records.

• Records are segmented into zones. A zone is a common namespace.

• DNS servers that host zones near the top of the DNS hierarchy can refer requests to DNS servers that host zones towards the bottom of the DNS hierarchy.

DNS Addresses• DNS addresses, also known as Fully Qualified Domain Name (FQDN), are a collection of zone information proceeded by a host name.

• Each element is separated by a period.

• A DNS address is read from back to front or right to left.

.auCountry Code

.edu.unimelblibrary

Top level domain

Organization domain name

Host name

• au, edu, and unimelb are all separate zones, hosted on separateDNS servers. Host name library is part of the unimelb zone.

Local DNS Servers• Almost all LANs have a local DNS server.

• Clients on the LAN address all DNS requests to the local DNS server.

• The local DNS server either returns the answer to the request from its own database, or it will query other DNS servers to locate the answer.

• In the past, DNS information was entered manually by administrators.

• Today, many DNS servers can be automatically updated, so that hosts that have different IP addresses can be easily contacted via DNS name.

DNS Resolution

DNS client host1.emcp.com queries its preferred DNS server. The DNS server in turn queries a series of DNS servers, beginning at the top of the DNS hierarchy until it returns a result from the server that holds the zone that the target host is located in.

DNS Name Space

Hierarchical Structure of DNS• Translates FQDN to IP• Root is the top of the tree (root domain) shown as . Period• Top level domains – indicate countries, regions, org type

– 2 letters for countries (US, UK FR, CA)– Countries sell their domain names, like Tuvalu (TV)– 3 letters indicate type of org (.com, .edu, .pro)

• Second level domains – variable length names register to individual or organization– Microsoft.com, cisco.com, sc4.edu, army.mil (parent domains)

• Sub-domain names – department or geographical location– Support, sales, training, south, west (child domains)

• Host domain – name assigned to a specific computer, this identifies the TCP/IP host, is seen as a leaf of the tree– Multiple host names can be associated with the same IP, but only one

host name can be given to a computer

DNS

• NetBIOS names go to Wins service, sends back IP• DNS – FQDN are no more than 255 characters long • IF FQDN name is requested to a DNS service, it will

return its IP• DNS clients are resolvers• DNS Servers are name servers• Host files were first used, became unmanageable• Recursive query – must have good answer or error• Iterative query – gives a best answer, it’s here or

here is the best chance place to look

A DNS Client Will Use a Recursive Query With the Preferred Server to Find an IP Address. While the Preferred Server Will Typically Use an Iterative Query to Discover the IP Address

Name and Address Resolution Done on an IP Network

Sample HOST File Works with DNS server.

Sample LMHOSTS File Works with WINS server.

5-4-3 RuleA consideration in setting up a tree topology using Ethernet protocol is the 5-4-3 rule. One aspect of the Ethernet protocol requires that a signal sent out on the network cable reach every part of the network within a specified length of time. Each concentrator or repeater that a signal goes through adds a small amount of delay time. This leads to the rule that between any two nodes on the network there can only be a maximum of 5 segments, connected through 4 repeaters/concentrators. In addition, only 3 of the segments may be populated (trunk) segments if they are made of coaxial cable. A populated segment is one which has one or more nodes attached to it .

5-4-3 Rule for an Ethernet Coaxial Network

5-4-3 Rule 10Base-T• What is the 5-4-3 Rule?

The 5-4-3 rule is a design guideline for 10baseT Ethernet Networks that make use of only hubs/repeaters and do not contain bridges, switches or routers, these devices negate the rule.

• What does the rule state?

For an Ethernet LAN of any size to operate the 5-4-3 rule must apply with regards to hubs. There may be a maximum of 5 segments between two hosts in a network, and there may be at most 4 hubs between these hosts and finally there may only be users on 3 of the segments.

• What are hosts?

Hosts may be servers, workstations or printers.

• This rule does not apply to other network protocols or Ethernet networks where all fiber optic cabling or a combination of a fiber backbone with UTP cabling is used. If there is a combination of fiber optic backbone and UTP cabling, the rule is simply translated to 7-6-5 rule.

10BaseT Network

5-4-3 Rule for an Ethernet UTP Network

Figure above shows the limits of the 5-4-3 rule where there are 4 hubs and 5 segments between the workstations on the left and the workstations on the right.

If a host was attached to the top hub and another host attached to the bottom hub? The 5-4-3 Rule would be violated, since there would be 6 hubs and 7 segments between 2 hosts.

How might I fix this violation?

Add a switch to the stack and modify how each hub is attached to the stack of hubs as shown in Fig. 2.

By inserting a switch into the stack as shown above any host to host communication will not violate the 5-4-3 rule regardless of where they are attached. Remember that the switch negates the 5-4-3 rule since there are not any more than 4 hubs/repeaters or 5 segments between any host attached with out passing through the switch. This is only one possible solution, there are many more.

5-4-3 Rule for an Ethernet UTP/Coaxial Network mixed.

Coaxial

UTP