Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Viewing debug ip rip results and configuring RIP2

This is driving me round in circles, finding it hard understanding the whole RIP concept.

The bit that confuses me is, you enable RIP2 on a router and you use the network command to list a classful network. Now if each router was also configured with the same config but with different classful networks, how come when viewing the debug ip rip results you see subnetted networks and not classful networks following the class a,b,c rules? I've just done the boson exam for the ICND1 and I set the exam topics to only provide router/routing protocols/router config/routing protocols trouble shooting questions and I scored 81% on 40 questions. The majority questions I scored incorrectly were regarding debug ip rip messages. Can anyone explain why in the debug ip results classless networks displayed?

8 REPLIES
Hall of Fame Super Silver

Re: Viewing debug ip rip results and configuring RIP2

Garry

I think there are some things in your question that I do not understand. Let me explain a few things and hopefully it will answer most of your question. If not then please ask further question so that I may understand it better.

First lets be clear about what the network statement does and the importance of entering a classful network in the network command for RIP. Some people believe that the network statement tells the routing protocol what to advertise. That is not true for the interior routing protocols like RIP. The function of the network statement is to tell the routing protocol what interfaces to include in the routing protocol.

So if you configure router rip with network 10.0.0.0 then RIP will look for all the interfaces on the router that fall into network 10.0.0.0 and will include those interfaces into the routing protocol. Once the routing protocol has included an interface it then looks at the address and subnet mask of the interface and based on these parameters RIP decides what to advertise.

So you enter classful network 10.0.0.0 as a network statement. Then when you look at the debug output you will see individual subnets of 10 being advertised.

So what is the deal with entering a "classful" network in the network command? Basically that is saying that the network statement can not get down to the subnet level in RIP. By comparison both OSPF and EIGRP allow the network statement to get down to the subnet level. But in RIP the entry must be at the network level and not the subnet level.

If I missed the mark in answering your question please help me understand better what you are asking.

HTH

Rick

New Member

Re: Viewing debug ip rip results and configuring RIP2

Rick, thats spot on!! i think my question should of been targeted at something like "When entering a network command in rip router mode, whats the reason for this?" :-).

Your response answered my question, i understand the reason for entering the classful network in rip router mode.

I understand the concept of Administrative Disatance, Metrics, Connected Routes, Default routes and the priority list of routing protocols etc.... It was just this classful network bit i was unsure of.

Thanks for this!

Garry

New Member

Re: Viewing debug ip rip results and configuring RIP2

Rick, thats spot on!! i think my question should of been targeted at something like "When entering a network command in router rip mode, whats the reason for this?" :-).

Your response answered my question, i understand the reason for entering the classful network in router rip mode.

I understand the concept of Administrative Disatance, Metrics, Connected Routes, Default routes and the priority list of routing protocols etc.... It was just this classful network bit i was unsure of.

Thanks for this!

Garry

Hall of Fame Super Silver

Re: Viewing debug ip rip results and configuring RIP2

Garry

I am glad that my answer was helpful. It is sometimes difficult to understand some of these terms and concepts - especially when you have a limited frame of reference to work from. The more you see of these things, it seems the more sense they make. For example I appreciate the difference much more having experience with OSPF and EIGRP which do permit subnet entries on the network statement. But you do not yet have that frame of reference.

There is a simple experiment that may help to clarify the concept of the classful network in the network statement for RIP. On a router that is running RIP assume that you have an interface with address 10.10.10.1 255.255.255.0. As an experiment configure router rip and input network 10.10.10.0. You will not get any error message about invalid entry. But when you look at the running config you will see that the IOS has turned your statement into network 10.0.0.0 (the classful network in the network statement).

HTH

Rick

New Member

Re: Viewing debug ip rip results and configuring RIP2

Ok great! I did read this in the last chapter regarding "Routing Protocols Concepts" but thanks again!

Just another quick question regarding RIP2, to my understanding when turning on RIP2, by default auto summarization is set. But lets say you enter the no auto-summary (cant remember the exact syntax) i guess you can be very flexible to which routes you avertise?

Hall of Fame Super Silver

Re: Viewing debug ip rip results and configuring RIP2

Garry

Yes auto summarization is enabled by default in RIPv2. And you have the option to turn it off if you choose.

Let me explore a bit what auto summarization is really about. Lets assume that we have a router with 2 interfaces. One interface has address 10.10.10.1 255.255.255.0 and the other interface has address 172.16.1.1 255.255.255.0. lets also assume that through the 10.10.10.1 interface the router has learned 3 other subnet in network 10. And assume that the router has learned 2 other subnets of 172.16 through the other interface. So a show ip route would have 3 learned subnets in 10 and 2 learned subnets in 172.16 plus the connected interfaces. With the default enabled of auto summarization the router would advertise out the 10.10.10.1 interface just a summary of 172.16.0.0 and not advertise the individual subnets of 172.16 that it knows. And similarly out the 172.16.1.1 interface the router would advertise only 10.0.0.0 and not the subnets that it knows.

But if you turn off auto summarization then the router would advertise individual subnets of 172.16 out the 10.10.10.1 interface and would advertise individual subnets out the 172.16.1.1 interface.

HTH

Rick

New Member

Re: Viewing debug ip rip results and configuring RIP2

Hi Rick, thanks for this again!! Finally, this is all coming together.

So its a vital that when configuring RIP2 as the routing protocol on, lets say in a network including 4 routers which each have 3 connected subnets, it is most important to add the correct classful networks to the router rip tables that have the subnets connected to its interfaces.

This helps a lot!

Hall of Fame Super Silver

Re: Viewing debug ip rip results and configuring RIP2

Garry

I am glad that it is all coming together. And I am glad that my information has helped you with your understanding.

Good luck as you continue your learning about Cisco networking. The forum is an excellent place to learn about Cisco networking and I encourage you to continue your participation in the forum.

HTH

Rick

530
Views
5
Helpful
8
Replies