rip v1 vs v2

[carl_townshend]

am i right in saying rip 1 v1 you cant use vlsm ? but with rip 2 you can ? does this mean that when you add networks into rip v2 you put in a subnet mask after the network statement ?

[pkhatri]

Hi Carl,

You cannot add a subnet mask when configuring the 'network' statement with RIPv2. However, the VLSM capability means that you RIPv2 will advertise networks with their subnets. For example, if you configure 'network 10.0.0.0' and there is an interface with an address of 10.1.1.1/24, RIPv2 will advertise a network of 10.1.1.0/255.255.255.0. With RIPv1, it would have only advertised 10.1.1.0.

Hope that helps - pls do rate the post if it does.

Paresh

[cisco]

Hi Paresh,

If suppose i am using RIPV1 and IGRP (Classfull Routing Protocols) in above scenario as mentioned by you . Now if i execute command "ip classless" the functioning of Clssfull Routing Protocol will change to Classless Routing Protocol means now in updates of RIPV1 or IGRP subnet mask will be advtertised ??

regards

Neo

[pkhatri]

Hi,

You should take note that the 'ip classless' command has nothing to do with the operation of RIP or IGRP. This command simply changes the way in which the Cisco router performs routing. When configured, the router will drop traffic destined to unknown subnets of a major network, instead of following the default route, if present.

Hope that helps - pls do rate the post if it does.

Paresh

[globalnettech]

Hello Neo,

in fact, RIpv1 and IGRP can simply not send routing updates for classless networks, that is, they can only send the classful networks 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.

The 'ip classless' command actually doesn't influence the way the routing table is built, it merely influences the forwarding decision is made. To give you an example, let's say your routing table has an entry for network 192.168.1.0, and your router gets a packet for IP address 192.168.2.23, without the 'ip classless' command configured on your router, packets for that destination would be dropped. 'ip classless' makes sure that the packet would get forwarded to the longest match. Check the link below for a somewhat more detailed info, and a configuration example:

IP Classless

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094823.shtml#classless

Regards,

GNT

[pkhatri]

GNT,

I think a clarification is in order here. RIP and IGRP are perfectly capable of sending non-classful network information. For example, RIP can send updates for 10.1.1.0 and 10.1.2.0 etc. The only thing it cannot do is to send network mask information. The network mask is inferred from the mask of the interface over which the updates are received.

Also, your example about 192.168.1.0 and 192.168.2.23 is not quite correct. Since we are talking about a class C network here, you can't really compare the two addresses, since they belong to different classful networks. A more accurate example would be a routing table with a route for 10.1.1.0 but not one for 10.1.2.0. Now, if this router receives a packet destined for 10.1.2.1, it will drop it if 'ip classless' is configured.

Paresh

[carl_townshend]

If I had the ip classless command configured and a default route present, would it use the default route, and if I used no ip classless would it not use the default route ?

[pkhatri]

It's actually the other way around. If you had the 'ip classless' command and a default route was present, it would NOT be used for unknown subnets of a classful network and vice versa. The bottom line is that the 'ip classless' functionality is deprecated and that's why it is no longer enabled by default.

Hope that helps - pls do rate the post if it does.

Paresh

[globalnettech]

Hello,

in addition to Paresh's post, just be aware that with RIP (version 2), the 'auto-summary' feature is enabled by default, which means that RIP will summarize prefixes to the classful network boundary. In the example above, with auto- summary enabled (the default), your router would still advertise 10.0.0.0/8, since that is the classful boundary. To turn that feature off, just use 'no auto-summary' in routing protocol configuration mode. That way, only your 10.1.1.0 network will get advertised...

HTH,

GNT

[pkhatri]

Thanks GNT, that certainly is a very good point and worthy of mention.

Paresh