ip classless & default route

[axfalk]

We're running MSFC's on Cat-6506s and are using static routes only; - i.e. no dynamic routing involved..The config had the "no ip classless" statement in it and we figured we would leave it intact..However, that resulted in the default route not working. Still, if we put a static route using the default route address, it would work OK. Does anybody happen to know what's going on here?

Thanks.

[Richard Burts]

Greg

The static route works because it is putting an entry into the routing table that the destination does match against.

When the IOS is making a routing decision for a packet it uses the destination address and does a lookup in the routing table. If the destination address does match a subnet or a network entry in the routing table then IOS knows exactly where to forward the packet. ip classless or no ip classless does not come into play in that situation. It is when the IOS does not find a subnet that matches and IOS is trying to determine whether to use the default route that ip classless or no ip classless becomes a factor.

HTH

Rick

[kramer700]

hey, no ip clasless will mess a lot of things and your default route , just remove it.

This is becouse the routing table acts clasfully, it will not forward with any classfull protocol either (RIPv1, IGRP), but everything which comes from classless protocol will be fine, i.e default route propagated thru OSPF will route.

Every Cisco router will do this, you can test it , or see CCNP Self study, Buldibg scalable cisco networks, p.104 thre is a example and explanation.

just go ip classless and you should be fine....

you are welcome