User guide

A-22 Cisco 2500 Series Access Server User Guide

Desktop Protocols

Figure A-8 Network Numbering Plan for IP, IPX, and AppleTalk

Node Addressing and Data Link Address Resolution

Each network protocol needs to able to uniquely address each node on a network. This

network layer node address may be the same as, or independent of, the already unique data

link layer address.

Once a packet has been routed to the correct network (data link), based on the network

number, it must be delivered to the correct node. Delivery of the packet on a network is done

using the Layer 2 (data link layer) address. A companion protocol performs resolution of

Layer 3 node address to the Layer 2 data link address. This companion protocol is called

the Address Resolution Protocol (ARP) for IP and AppleTalk Address Resolution Protocol

(AARP) for AppleTalk. IP and AppleTalk both use ARPs but IPX does not, because the IPX

48-bit node address is always the same as the 48-bit data link address. The ARP must be

working correctly in order to maintain connectivity between the devices in an internetwork.

Router A

FDDI

Token

Ring

Router B

Router C

Router D

172.16.10.0

B010

1001–1002

172.16.30.0

B030

3001–3002

172.16.20.0

B020

2001–2002

172.16.1.0

B001

10-10

172.16.2.0

B002

20–20

172.16.40.0

A001

100–100

H3546