Autosummarization Support and Configuration

Some classless routing protocols support autosummarization, defaulting to use it, but with the ability to disable it with the no autosummary router subcommand.

Routing Protocol Classless? Supports Autosummarization Defaults to Use Autosummarization? Can Disable Autosummarization?
RIP-1 No Yes Yes No
RIP-2 Yes Yes Yes Yes
EIGRP Yes Yes Yes Yes
OSPF Yes No - -

Autosummary impacts routers that directly connect to parts of more than one classful network, but it has no impact on routers whose interfaces all connect to the same single classful network.