Suppose the router's routing table has only two entries:
172.16.10.0/24 via e0
*0.0.0.0/0 via e1
and two packets with dest. ip address 172.16.20.1 and 10.1.1.1 respectively come into the router.
Here is what happen when classful routing is configured:(use no ip classless)
1.The router match the network number first. Because 172.16.20.1 belongs to the classful network 172.16.0.0/16 and the routing table entry 172.16.10.0/24 is also belongs to the same classful network 172.16.0.0/16, the routing process consider this is a match and goto step 2.
On the other hand, 10.1.1.1 belongs to the classful network 10.0.0.0/8 and there is no routing entry belongs to the same classful network 10.0.0.0/8, routing process consider this is no-match and goto step 3 (that is, skip the step 2)
2.Then the router will do a longest match inside that classful network 172.16.0.0/16. (this is the key point: it will not do a longest match outside the classfull network). For packet with dest. ip address 172.16.20.1, there is no match under this step. So the router drops the packet and ends the matching algorithm.
3.the 10.1.1.1 packet will match the routing entry 0.0.0.0/0 and be routed via e1.
In case of classless routing, the algorithm is simple: just do a longest match. Both packets will end up with matching the 0.0.0.0/0 entry and routed via e1.
This is actually a pretty cool feature, i didn't even know it existed until I was looking for a solution to advertise a subnet (prefix in BGP talk), only if a certain condition existed. This is exactly what conditional advertisements does
j ai une question j ai achete un routeur cisco 887VA-k9 , je le configuré avec la configuration ci- dessous
si je le lier avec mon pc portable sur l un de ses ports directement ça marche toute est bien ( la connexion internet + m...
Attached policy provides CLI access to the Cisco 4G router over text messaging. Two files are in the attached .tar file:
2. PDF with instructions on how to load and use the .tcl file.