RIPv1 Confused

Hi All,

I'm a bit confused with the RIPv1. Iv been reading around the net trying to get a better understanding of how it works however its left me more confused in regards to what Subnet masks I can use.

In almost every example they use a Class A,B or C subnet mask throughout the topology as VLSM is not supported in this version.

Im trying to find out if I can take a class A address and use a /25 subnet mask throughout my whole topology then implement RIPv1. Iv been playing around in packet tracer but not having too much luck.

My understanding is you can use any subnet mask as long as ALL networks use the same one. Is this correct? or am I just limited to /8 /16 /24?

Appreciate if anyone may be able to clear this up for me :)Thanks!
Rev.

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Comments

Bl8ckr0uter

Revenue wrote: »

Hi All,

I'm a bit confused with the RIPv1. Iv been reading around the net trying to get a better understanding of how it works however its left me more confused in regards to what Subnet masks I can use.

In almost every example they use a Class A,B or C subnet mask throughout the topology as VLSM is not supported in this version.

Im trying to find out if I can take a class A address and use a /25 subnet mask throughout my whole topology then implement RIPv1. Iv been playing around in packet tracer but not having too much luck.

My understanding is you can use any subnet mask as long as ALL networks use the same one. Is this correct? or am I just limited to /8 /16 /24?

Appreciate if anyone may be able to clear this up for me :)Thanks!
Rev.

That is my understanding. You can use none standard mask but you can only use the same mask.

I could be wrong.

KPWright

I don't know a whole lot, but I'll take a stab at this one and let others burn me if I'm wrong.

Identifying anything other than the standard classful mask won't make any difference if you are using RIPv1 as it is a strictly classful protocol. It may have an affect on other components in your configuration and your network, but not to the RIP routing. If you want to run RIP and use classless addressing, it's version 2.

From Wikipedia:

RIP version 1
The original specification of RIP, defined in RFC 1058,[3] uses classful routing.

The periodic routing updates do not carry subnet information

, lacking support for variable length subnet masks (VLSM). This limitation makes it impossible to have different-sized subnets inside of the same network class. In other words, all subnets in a network class must have the same size.

jason_lunde

Please read this post...especially the main post, and edTheLad's therein...
http://www.techexams.net/forums/ccna-ccent/46974-classless-vs-classful-regards-rip.html

Cheers!

mikej412

Revenue wrote: »

My understanding is you can use any subnet mask as long as ALL networks use the same one. Is this correct?

Correct. RIPv1 can deal with subnetted networks as long as the subnets are in the same major network and all have the same subnet mask.

Revenue

Thanks for your responses!

Appreciate the help. Would route summarization come into play with RIPv1 at all?

I Haven t really read up to much on it but in using a non standard subnet mask would this cause any issues? An example a guy on my course gave me was:

the problem is that, for example, it will advertise 192.168.0.4/30 and 192.168.0.8/30 and 182.168.0.12/30 all under the classful address of 192.168.0.0

This makes it tricky, because the router now only has one route in it's routing table. so it will send packets destined for three different networks through the same next hop. Which may work, depending on circumstances, but could easily fail.

What if the next hop for 192.168.0.4/30 is out s0/0/0, but the next hop for 192.168.0.8/30 is out s0/0/1? it will have one route in the routing table (192.168.0.0), but it will be an equal cost route.

In this case some packets go out one interface and some out the other.

This still confuses me haha! Maybe I need to go back to the books on this one >_<