VLSM-OSPF Lab

Objectives

• Create a multi-router network topology

• Design an IP addressing scheme using a Class C network address and VLSM

• Apply IP addresses to the routers

• Test the topology to verify IP connectivity

Preconfigs

· Note: The “no keepalive” command is added to FastEthernet0/0 interface. This will bring the interface up without having to connect a switch or a hub.

Background / Preparation

You are responsible for designing a network that interconnects 3 geographically separated sites,

each with its own LAN. You have a class C network address to work with and must make the best

use of the address space while minimizing wasted addresses. To accomplish this you will develop

an IP addressing scheme using Variable Length Subnet Masks (VLSM) to allocate IP addresses to

the LANs and WAN links in the network. You will apply the addresses to the routers and

workstations in the simulated network and then test to ensure that it works.

Routers simulated with Packet Tracer use RIP version 2 to find routes to remote networks

automatically. A router advertises all networks that its ports belong to, which is specified by the IP

address and subnet mask. RIP version 2 supports VLSM. RIP keeps a routing table of remote

networks. The routing table associates a network (network ID and subnet mask or network bits) to

the port on that is closest to the network. A router can have one default port.

Step 1. Design an IP Addressing Scheme Using VLSM

Starting with the Class C network address of 192.168.1.0/24, create subnets to allocate IP

addresses to the Ethernet LANs and WAN links in the network topology shown above. The design

requirements for the number of addresses are listed in the table below. Use VLSM to minimize

wasted IP addresses. Assume ip subnet-zero is enabled and that the first subnet (all zeros) and

last subnet (all ones) can be used.

As a general rule it is best to first allocate subnets to the networks with the largest number of

required hosts starting from the lowest subnet number and working up. Ethernet networks will

require more IP addresses than WAN links. Be sure to minimize the number of addresses used on

the WAN links and allocate WAN subnets starting at the highest subnet. Document your VLSM

subnet design using the table below. You will use these subnet address ranges to assign interface

addresses to the routers and workstations in the scenario.

Notes:

55 hosts require at least 6 bits ~ 111111 = 63

26 hosts require at least 5 bits ~ 11111 = 31

12 hosts require at least 4 bits ~ 1111 = 15

2 hosts require at least 2 bits ~ 11 = 3

192.168.1.0/26

This means that the first two bits will be set to 00.

00000000 through 00111111 in binary

0 through 63 in decimal

192.168.1.64/27

This means that the first three bits will be set to 010.

01000000 through 01011111 in binary

64 through 95 in decimal

192.168.1.96/28

This means that the first four bits will be set to 0110.

01100000 through 01101111 in binary

96 through 111 in decimal

192.168.1.248/30

This means that the first six bits will be set to 111110.

11111000 through 11111011 in binary

248 through 251 in decimal

192.168.1.252/30

This means that the first six bits will be set to 111111.

11111100 through 11111111 in binary

252 through 255 in decimal