Hi,
The 'no ip classless' command makes your router work in a classful fashion. The impact of using this is that there is a likelihood that some subnets will be black-holed.
Here's an example:
- 'no ip classless' is enabled
- there are two routes in the routing table:
10.1.1.0/255.255.255.0
0.0.0.0/0.0.0.0 (default)
- If your router receives a packet with a destination of 10.20.1.1, it will discard the packet instead of using the default route. This is because a subnet of the 10.0.0.0/8 classful address exists in the routing table (the 10.1.1.0/24 subnet). The router assumes that that is all there is to know about the 10.0.0.0/8 network. Any other subnets of 10.0.0.0/8 are considered unreachable (unless specific routes for those are present as well).
- if 'ip classless' were configured instead, the default would have been used.
Hope that helps - pls rate the post if it does.
Paresh
