Lab 2.7.1 IP Unnumbered and Discontiguous Networks -- Configuring IP Unnumbered

Objective:

Demonstrate how improper IP addressing can have a negative impact on a network and the use of IP Unnumbered on a point to point serial link to save IP addresses.

Background:

Your company obtained an outside contractor to setup a basic network which would connect three different areas of the company. These areas do not need to access any other networks or the Internet. The resulting basic network is shown above in the graphic. The network does not operate as anticipated and it is your job to fix it.

Equipment:

Three Routers Three Switches Three workstation

Step 1

Build the network in the above diagram. Use RIP or IGRP as your routing protocol

Step 2

  • Turn on Debug All on Router-A Ping S0/0 on Router-A from 168.71.8.2 workstation. Watch Router-A's debug information.

What happened?

Step 3

  • Turn on Debug All on Router-C Ping Ethernet 0/0 on Router-A from 168.71.8.2 workstation. Watch Router-C's debug information.

What did you see?

Step 4

  • On Router-A type sh ip route
  • On Router-B type sh ip route
  • On Router-C type sh ip route

Describe the journey of the ICMP packets.

Step 5

  • Change the address on the 172.32.0.0 serial link so that the interfaces are in the 168.71.4.0 network.
  • Ping from the workstation on network 168.71.5.0 to the workstation on 168.71.8.0

Were you successful?

Look at the routing tables Question - Determine what is reachable on the overall network?

Step 6

Configure IP unnumbered on the serial links.

  • On each serial interface enter ip unnumbered fa 0/0 (or correct ethernet port)

Will the workstations be able to communicate?

  • List the entries in the routing table

What is the main purpose of IP unnumbered?

Step 7

  • Change the IP address of Ethernet0 on Router C to 168.71.8.17 255.255.255.240
  • Clear the routing table using the command clear ip route *

Can the workstations communicate? Why?

  • List the entries in the routing table

What changed in the routing table from step six to step seven?

Step 8

  • Change the IP Address of Ethernet 0 on Router C to 168.72.8.1 255.255.255.0
  • Clear the routing table using the command clear ip route *

Can the workstations communicate? Why?

Reflection:

Answer the following questions.

What benefit is gained by using IP unnumbered?

How were the routers able to successfully forward packets using IP unnumbered?

Challenge Exercise:

Can the five router lab from semesters 1-4 be configured to support IP unnumbered?

  • Record the contents of the routing table on one of the routers.
  • Configure the network to support IP unnumbered.
  • Compare the contents of the routing table using IP unnumbered to the routing table with subnets on the links.

How many subnets have been saved?

How does the router know how to forward packets on the network?