why doesn't router table (rip) show correct network address ?

dannan lin · ‎10-05-2011

The address i gave was 10.1.1.1/24 , in this case the correct netowrk address should be 10.1.1.0 /24

not 10.0.0.0/24 .

why does this happen? I have tried RIPv2 but it did not change . below is my routing table.

10.0.0.0/24 is subnetted, 1 subnets

C 10.1.1.0 is directly connected, Serial2/0

R 11.0.0.0/8 [120/1] via 10.1.1.2, 00:00:18, Serial2/0

[120/1] via 12.1.1.2, 00:00:06, Serial3/0

12.0.0.0/24 is subnetted, 1 subnets

C 12.1.1.0 is directly connected, Serial3/0

C 192.168.1.0/24 is directly connected, FastEthernet1/0

R 192.168.2.0/24 [120/1] via 10.1.1.2, 00:00:18, Serial2/0

R 192.168.3.0/24 [120/1] via 12.1.1.2, 00:00:06, Serial3/0

thanks for your help.

flokki123 · ‎10-06-2011

hi dannan,

ripv1 is a classful routing protocol, which means it always uses only the class A,B or C network number.

When you enter the network with the "network" command you only enter the class A,B or C network number.

E.g.: the ip 10.1.1.1/24 is subnetted but still is by nature a class A ip address. so if you want to enter this ip with ripv1 you would have to enter 10.0.0.0 -> only the class address!

class A: 10.0.0.0 to 10.255.255.255

class B: 172.16.0.0 to 172.31.255.255

class C: 192.168.0.0 to 192.168.255.255

HTH,

florian

dannan lin · ‎10-06-2011

thanks florian .

forgive me, i am newbie to cisco.

I have a question here,

I have tried using ripv2 and truned off the auto summary.

Router(config)#router rip

Router(config-router)#ver 2

Router(config-router)#no auto

Router(config-router)#no auto-summary

the output of routing table is like below:

10.0.0.0/24 is subnetted, 1 subnets

C 10.1.1.0 is directly connected, Serial2/0

11.0.0.0/24 is subnetted, 1 subnets

R 11.1.1.0 [120/1] via 10.1.1.2, 00:00:19, Serial2/0

[120/1] via 12.1.1.2, 00:00:28, Serial3/0

12.0.0.0/24 is subnetted, 1 subnets

C 12.1.1.0 is directly connected, Serial3/0

C 192.168.1.0/24 is directly connected, FastEthernet1/0

R 192.168.2.0/24 [120/1] via 10.1.1.2, 00:00:19, Serial2/0

R 192.168.3.0/24 [120/1] via 12.1.1.2, 00:00:28, Serial3/0

compare to original , it contained more information but I still can't see the advantages of using RIPv2

. I know RIPv2 supports classless IP address but still, from routing table I can not see correct network address (which should be 10.1.1.0/24) .

could you explain this for me. much appreciated.

flokki123 · ‎10-06-2011

the biggest difference between classful and classless routing protocols is, that classful routing protocols dont send the subnet mask and classless protocols do send the subnet mask with the routing updates.

cant tell you if the routing table should look different. would have to try it myself.

if a ripv1 router receives a rip update it assumes that the received route has the same subnet mask as the interface which received the update. it has to assume, as there is no mask in the update itself. thus this could cause problems.

at heart ripv2 is still a distance vector protocol. i think next to the advantage that ripv2 send the subnet mask with routing updates, other enhancements are ripv2 uses multicasts instead of broadcasts for updates and ripv2 supports triggered updates(as soon as a change happens updates will be send).

iam not a expert in this topic either, but hope you can understand it now a bit better.

regards,

florian

johnlloyd_13 · ‎10-06-2011

Hi Dannan,

The 10.1.1.0 is the actual route for the directly connected network. This is called a level 2 route or also known as a child route. It contains the following information:

C - The route code for directly connected network

10.1.1.0 - The specific route entry

is directly connected - Along with the route code of C, this specifies that this is a directly connected network with an administrative distance 0

Serial2/0 - The exit interface that match this route entry.

You will notice that the subnet mask is not included for the child route. The subnet mask for this child route is also a /24 which is included in its parent route 10.0.0.0/24.

Sent from Cisco Technical Support iPhone App

Richard Burts · ‎10-06-2011

Dannan

I believe that what the router displays is correct - especially if you think about it from the router perspective. Here is the important part of the output from your original post.:

10.0.0.0/24 is subnetted, 1 subnets

C 10.1.1.0 is directly connected, Serial2/0

From the router perspective there is one "network" and one "subnet". The "network" is the class A network 10.0.0.0. And that is what the first line of output is telling you. The network is subnetted into /24 which is also indicated in the first line of output. Then the router gives information about the subnet which is 10.1.1.0 in the second line of output.

Perhaps part of the confusion is that you are looking for the router to describe a single address (network/subnet) because you only configured one. But the router is giving both a network address and a subnet address. And technically the network address is the class A 10.0.0.0.

HTH

Rick

HTH

Rick

dannan lin · ‎10-06-2011

thanks for your guys help.

but I still want to know what are the key advantages of RIP v2, i know it supports CIDR and vlsm.

but no matter I use RIP v1 or RIP v2 the routing table still looks the same.

i.e. below is rip v2 routing table

10.0.0.0/25 is subnetted, 1 subnets

C 10.1.1.0 is directly connected, Serial2/0

R 190.10.0.0/16 [120/1] via 10.1.1.126, 00:00:21, Serial2/0

C 192.168.1.0/24 is directly connected, Loopback0

R 192.168.20.0/24 [120/2] via 10.1.1.126, 00:00:21, Serial2/0

below is rip v1 routing table

10.0.0.0/25 is subnetted, 1 subnets

C 10.1.1.0 is directly connected, Serial2/0

R 190.10.0.0/16 [120/1] via 10.1.1.126, 00:00:01, Serial2/0

C 192.168.1.0/24 is directly connected, Loopback0

R 192.168.20.0/24 [120/2] via 10.1.1.126, 00:00:01, Serial2/0

i know RIPv2 supports classless routing but from the table i see no differences, and more importantly both routing table looks exactly the same. is there any experiments i can do to see the differences in RIPv1 and RIPv2??

thanks for your help.

Richard Burts · ‎10-06-2011

Dannan

There are several advantages to RIPv2 and there are experiments that you can do that will show them. Let me make a few suggestions:

- support for VLSM. to demonstrate this use 2 routers. On routerA create several interfaces/subnets. To make it easy create subnets in class A network 10.0.0.0. Create one subnet as 10.1.1.0/24, a second subnet as 10.2.2.0/26 and a third subnet as 10.3.3.0/28. Connect routerB to routerA on one of those subnets. Run RIPv1 on both routers and look into the routing table of routerB. You will find that the other 2 subnets are not advertised because RIPv1 requires that all subnets be the same size. Then run RIPv2 on both routers. Look into the routing table of routerB. You should find the 2 subnets are now advertised.

- ability to control summarization. to demonstrate this use the 2 router setup. On routerA create interfaces with subnets of a class B network. Perhaps use 172.16.1.0/24, 172.16.2.0/24, 172.16.3.0/24 and configure an interface in class C 192.168.1.0. Connect routerB to routerA on the 192.168.1.0 interface. Run RIPv1 on both routers. Look in the routing table of routerB. You should find that RIP has automatically summarized the class B 172.16.0.0 and that the routing table on routerB has only a single entry for 172.16.0.0/16. Then configure both routers to run RIPv2 and on routerA under RIPv2 configure no auto-sum. Then look in the routing table of routerB. You should now find that the routing table of routerB has the 3 subnets and not just the one summarized entry.

HTH

Rick

HTH

Rick

dannan lin · ‎10-07-2011

thanks all your help. much appreciated.

dannan lin · ‎10-08-2011

thanks richard , you cleared my confusion . much appreciated