Chapter 3

How to configure a Network?

Johny : Dad, My school has a branch at Noida. We want into interconnect the computers of both these campuses. Can you explain, in a simple way, how to do this? The following is the network diagram:

Johny : I am little confused. School-1 has one network and School-2 has another network. So there are only TWO networks?

Dad : In addition to these TWO LAN NETWORKS, there is a WAN network which connects one Router-1 to Router-2.

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Dad : The first thing you should know is, how many networks are there in above  diagram. I have redrawn the diagram to make this point clear :

Can you find out how many networks are there in this diagram. There are nine networks.

Dad: The next step is, we should allot  IP addresses for each network. The very simple method is :

Johny : What is the meaning of  /24  in  10.1.1.3/24 ?

Dad :  Slash 24 is the subnet mask expressed in slash notation. It is same as 255.255.255.0.

Beacause 255.255.255.0 is nothing but 24 ONES followed by ALL ZEROS.

Johny: How to calculate Network ID of Network-1?

Dad :            Take any IP Address and its subnet mask from Network-1. From this information, you should be able to calculate NETWORK ID,BROADCAST ADDRESS and IP ADDRESSES OF ALL HOSTS in that network.

For Example,Let us take 10.1.1.3/24.

Here 24 means, FIRST 24 BITS of 10.1.1.3  REPRESENTS NETWORK NUMBER,

0000 1000. 0000 0001. 0000 0001.0000 0000 =10.1.1.0= Network ID

0000 1000. 0000 0001. 0000 0001.0000 0001  = 10.1.1.1 =Host

0000 1000. 0000 0001. 0000 0001.0000 0010  =10.1.1.2= Host

0000 1000. 0000 0001. 0000 0001..................  =10.1.1.3 to 10.1.1.253=hosts

0000 1000. 0000 0001. 0000 0001.1111 1110  =10.1.1.254=host

0000 1000. 0000 0001. 0000 0001.1111 1111  =10.1.1.255 = Broadcast Address

Johny : Can you explain the same thing for  10.1.2.2/30 ?

Dad :               Slash 30 is the subnet mask expressed in slash notation

Here 30 means, FIRST 30 BITS of 10.1.2.2  REPRESENTS NETWORK ID,

0000 1000. 0000 0001. 0000 0010 0000 0000 =10.1.2.0 = Network ID

0000 1000. 0000 0001. 0000 0010.0000 00 01 =10.1.2.1 = Host

0000 1000. 0000 0001. 0000 0010.0000 00 10  =10.1.2.2 = Host

0000 1000. 0000 0001. 0000 0010.0000 00 11  =10.1.2.3 = Broadcast Address

Johny : Still this concept is not clear,dad.

Dad : Try to calculculate the Network ID,Broadcast Address and the List of IP Addresses of hosts  for the  following cases. Then you will understand.:

1) 61.1.0.5/24   2) 210.212.90.43/26   3) 192.168.1.89/30   4) 172.16.1.100/16

Johny: How to actually put 10.1.1.3/24 in a computer?

Dad : In cases Windows computers, Select Start > Settings > Control Panel > Network Connections >

Local Area Network > Properties > Internet Protocol(TCP/IP) > Properties > Now you can enter the IP address (10.1.1.3), Subnet Mask (255.255.255.0) which is same for all the computers in that network, then Default gateway (10.1.1.1) which is nothing but the IP address of the Router in that network. See the screen shot.

Johny : How to configure IP address in Router-1?

Dad : Our Router-1 has two interfaces. One is Ethernet and another one is serial. Ethernet is used for connecting to the LAN network. Serial interface is for connecting to WAN network. Do the following steps to configure IP address in the Router.

STEP-1 : Connect your Windows PC's COM1 to the Console Port of the Router.

STEP-2 : Select HyperTerminal Program :

STEP-3: Type Some name for the Connection Description and Press OK.

STEP-4 : Select the Port in which  your cable is terminated ( In this case it is COM1 port)

STEP-5 : Set the COM-1 Properties to (9600,8N1,FlowContrl=None) :

Step-6 : That is all. Just Press the Enter key of your PC one or two times.Wah! Router will talk to you. Let us configure the Ethernet Port of Router1.

Router1 Con0 is now available

Press Return to get started. ( Now I am pressing Enter key)

User Access Verification

Password: xxxxx  (Now I am entering the password)

Router1>enable  (I got 'GreaterThan' prompt. Now I type enable to go into Privileged mode)

Password : xxxxx  ( Now I am entering enable password)

Router1 #config terminal  ( I got # prompt. Now I type the command to go into configuration mode)

Router1(config)#interface ethernet0 ( Now I am ready configure ethernet0 interface)

Router1(config-if)# ip  address 10.1.1.1  255.255.255.0 ( Now I enter IP address and subnet mask)

Router1(config-if)# no shutdown  ( I enabled the interface)

Router1# ^z  ( I came out of configuration mode)

Router1# write mem  ( I am saving the configuration)

Johny : Dad,Explain how to configure the Serial 1 port with IP address 10.1.2.1/30.

Dad :

Router1 #config terminal  ( I got # prompt. Now I type the command to go into configuration mode)

Router1(config)#interface serial0 ( Now I type the name of the interface I am going to configure)

Router1(config-if)# ip  address 10.1.2.1  255.255.255.252 ( Now I enter IP address and subnet mask)

Router1(config-if)# no shutdown  ( I enabled the interface)

Router1# ^z  ( I came out of configuration mode)

Router1# write mem  ( I am saving the configuration)

Johny : Dad, what is routing table and how to configure routing table in my routers?

Dad : Carefully watch the complete network diagram. Now, tell me how many networks are there in the diagram.

Johny : Totally three networks.

Dad : Good.  Do you know, already we having configured the routing table for TWO networks. Carefully examine our interface configuration and you can read between lines ' All the hosts in the range of  10.1.1.1 to 254 are reachable through Ethernet0'. ' All the hosts in the range of 10.1.2.1 to 2 are reachable through Serial 0'.

Johny: Yes. But what about the THIRD NETWORK?

Dad: That is what we have to configure now.

Router1 #config terminal  ( I got # prompt. Now I type the command to go into configuration mode)

Router1(config)#ip route 10.1.3.0 255.255.255.0  serial0

Note : The above command can be written using another method :Instead of giving the interface name such as serial0, you can give the IP address of the OTHER END. Like this >>Router1(config)  # ip  route 10.1.3.0 255.255.255.0  10.1.2.2

Router1# ^z  ( I came out of configuration mode)

Router1# write mem  ( I am saving the configuration)

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Have a look at this animation also.Routing configuration Animation