RIP & IGRP

[arivukalanjiyam]

I read it in Boson e-book that RIP & IGRP are "classful" protocols and hence they don't understand a subnet mask of 32 0s,and hence cannot route to the default route even if it is mentioned in the routing table.

and also to avoid this they have given a command
Router(config)#ip classless

what does all this mean???

Please help me!

 

[svermill]

http://www.cisco.com/en/US/partner/tech/tk648/tk365/technologies_tech_note09186a0080094823.shtml

 

[jgercken]

Classful protocols assume networks follow the A,B & C sizes and doesn't use netmasks. If you are using the IP 10.10.1.1 it assumes the network is the class A 10.0.0.0.

IP classless command tells the router that you want to break from the rigid A,B,C classes and have varying size subnets by using netmasks.(VLSMs) No can't do this with RIP v1/IGRP since they don't send the netmasks in their updates. ----------------------------------------
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[svermill]

Jgercken,

That isn't exactly correct. Use of the 'ip classless' command is used where classful routing protocols exist. When you subnet a major network, a classful protocol assumes the entire network uses the same mask. If a router has a default gateway, and it receives a packet for a subnet it isn't aware of, it will drop the packet instead of forwarding it on to the default gateway. A router with the 'ip classless' statement will use a route with a *shorter* mask than what it is configured with (e.g. 0.0.0.0 0.0.0.0). This prevents packet loss.

http://www.cisco.com/en/US/tech/tk648/tk365/technologies_tech_note09186a0080094823.shtml#classless

Regards.