Hello Chandrasekhar
The auto-summary command restores the default auto summarization behaviour of the routing protocol. RIP Version 1 always uses automatic summarization. If you are using RIP Version 2, you can turn off automatic summarization by specifying the no auto-summary command. Disable automatic summarization if you must perform routing between disconnected subnets. When automatic summarization is off, subnets are advertised. Note that this is a command implemented generally for the whole router under the RIP configuration.
On the other hand, the ip summary-address command that you stated indicates to the router how to summarize routes on specific interfaces. Notice that the command is implemented on the interface. You can specify how summarization takes place, in a different manner than the default.
The address after the “via” in the output shows the best next-hop address. If the field is set to 0.0.0.0) the address of the advertising router is the best next-hop address.
I hope this has been helpful!
Laz