ICTP - URSI SCHOOL ON DIGITAL AND MULTIMEDIA COMMUNICATIONS USING TERRESTRIAL AND SATELLITE RADIO LINKS 12th February - 2nd March 2001 , Trieste (Italy)
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	Exercises on Routing : changing the topology of the local network

• 1. Planning of the new network topology
• 2. Configuration of the routers
• 3. Configuration of the hosts
• 4. Setup of physical connections
• 5. Test of the network

Task 1: Planning of the new network topology

Objectives:	To change the room network from the actual topology (common bus for all PCs) to a new structured one with 4 subnets locally interconnected by routers and then to the building network
Method:	Subdivide the "class C like" network 140.105.45.0 into more smaller subnets (4 for the groups, one more for the routers network)
Comments:	All groups should cooperate to the "high level" planning of the new network (subnets distributions) and all components of each group should cooperate to the "local" planning (addresses distribution inside the group)

 

Activity 1.1 Design of the new topology

The firts step is to draw a schematic rapresentation of the new network.

Consider the following pictures:

The actual network topology:



The new requested network topology:

Now sketch two simple rapresentations of them, something like this:

Activity 1.2 Find the numbers

For the whole room network we have obtained a class-C like network:
the network is the 140.105.45.0
(that means 254 possible hosts, from 140.105.45.1 up to 140.105.45.254)
But now we need a total of at least 6 networks (5 groups plus a routers network)...
So we should do subnetting.

Try to figure out any possible way to subnet a class-C network:

• 1 network of 254 hosts (that means "no subnetting");
• 2 networks of 126 hosts each;
• 4 networks of 62 hosts each;
• 8 networks of 30 hosts each;
• 16 networks of 14 hosts each;
• 32 networks of 6 hosts each;
• 64 networks of 2 hosts each;
• 128 networks with no hosts (hmmm, I think that this will not be useful...).

After all groups came on a common decision about the subnetting, they should distribute the new subnets to the groups and agree for the router addresses.

Then add all the numbers (NIC addresses) to the previous drawing and check it carefully!
You should obtain something like this:

Task 2: Configuration of the routers

Objectives:	To configure the routing tables for the 4 group routers
Method:	Using the commands ifconfig and route or the netcfg utility
Comments:	On the routers you will have already installed 2 ethernet cards. Check if there are properly recognized from the kernel. And remember to disconnect physically all the interfaces before doing routing configuration!

 

Activity 2.1

First you should assign the ip addresses to the two network interface.
Then you should define a network entry for the routers subnet through the first network interface and a network entry for the group local subnet through the second one.
You'll need also entries for all the other group subnets, pointing to the correct group routers.
And finally don't forgot the default route entry, that will point to the main room router.

Task 3: Configuration of the hosts

Objectives:	To configure the routing tables for all the hosts
Method:	Using the commands ifconfig and route or the netcfg utility
Comments:	Remember to disconnect physically the network interface before doing network configuration!

 

 Activity 3.1

You should define the ip address and then a network entry for the group local subnet.
And of course the default route entry, that will point to the group router.

Task 4: Setup of physical connections

Objectives:	To physically connect to the network all hosts and routers.
Method:	You will use UTP cables and Ethernet Switches.
Comments:	Pay attention to use the proper type of cable (plain cables, not crossed ones)!

 

 Activity 4.1

Connect every hosts and routers to the switches.
Handle carefully cables and connectors to avoid failures and malfunctionings and use patch panels to obtain a "clean" wiring.

Task 5: Test of the network

Objectives:	To check if the network has been properly configured and wired and is therefore working.
Method:	Using the ping and traceroute commands
Comments:	If the test fails review the configuration with ifconfig and route -n commands, then check the cables. Use only ip numbers and not domain names.

 

 Activity 5.1

First test the local connectivity, i.e. the possibility to ping from one host to an other in the same group and to the group router.
Then check if you can reach the room main router from your hosts, and finally try to ping some hosts of the other groups.
Hopefully at this time you will be able to reach every host connected to Internet.