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. And see here for current known issues.

New Member

ip classess command

I was told by a tutor that this just changes the way the router thinks and its nothing to do with the routing protocols ? is this true and what exactly does it do ?

1 REPLY
Cisco Employee

Re: ip classess command

Carl,

The exact purpose of this command is to force the router to adopt a classless behavior as its name indicates. And it is correct that it doesn't applt the routing protocols as such.

Here's an example of when classfull behavior is configured (no ip classless). The router receives a packet with a destination address of 172.16.19.1 and there is already a route in the RIB for another subnet belonging to the same classfull network, let's say 172.16.18.0/24. The router tries to resolv the destination address using the classfull network and drops the packet if there is not matching subnet even if a default route exists in the RIB. In other words, the classfull behavior will not allow resolution outside the classfull network.

On the other hand, if a classless behavior is configured (ip classless) the router sear for the best match in the RIB and will use the default route if no better router exists.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
109
Views
4
Helpful
1
Replies
CreatePlease login to create content