Discontiguous Classful Networks
 


Autosummarization does not cause any problems as long as the summarized network is contiguous rather than discontiguous.

- Contiguous network: A classful network in which packets sent between every pair of subnets can pass only through subnets of that same classful network, without having to pass through subnets of any other classful network.

- Discontiguous network: A classful network in which packets sent between at least one pair of subnets must pass through subnets of a different classful network.

Autosummarization prevents an internetwork with a discontiguous network from working properly.  Autosummarization would cause load balancing to occur if s0/0 and s0/1 were both pointing to a 10.* network.  Which is bad if you don’t want to load balance, as autosummarization assumes 10.0.0.0/8.

The solution to this problem is to disable the use of autosummarization.  Because classful routing protocols must use autosummarization, the solution requires migration to a classless routing protocol and disabling the autosummarization feature.