ip classless

pannupandit

guys I want some thorough explanation abt this command.I know that we basically use it with default routing.But I am not able to get into the picture.If anybody has any tutorial. DO give me or if anybody knows plz tell me.

Thanx
Pannu

agustinchernitsky

According to Cisco Cmd Ref:

This command allows the software to forward packets that are destined for unrecognized subnets of directly connected networks. The packets are forwarded to the best supernet route.

When this feature is disabled, the Cisco IOS software discards the packets when a router receives packets for a subnet that numerically falls within its subnetwork addressing scheme, no such subnet number is in the routing table and there is no network default route.

EdTheLad

pannupandit wrote:

guys I want some thorough explanation abt this command.I know that we basically use it with default routing.But I am not able to get into the picture.If anybody has any tutorial. DO give me or if anybody knows plz tell me.

Thanx
Pannu

If you have "no ip classless" the routing table will work matching the inital bits of an ip address which correspond to the class address.
I.e 01 class A, 10 class B, 110 class C
If a packet arrives with an ip address 13.1.1.1, the routing table will see its a class A address indicated by the 01 inital bits and then the table will try and find if the major network 13.x.x.x is in the table,if not the default route will be used, if present the particular subnet is checked,if the subnet exists the packet is forwarded,if the subnet doesnt exist the packet is discarded.