Please check below link :
http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml#defaultrouting
***Quote start
Default Routing
There are two ways to inject a default route into EIGRP: redistribute a static route or summarize to 0.0.0.0/0. Use the first method when you want to draw all traffic to unknown destinations to a default route at the core of the network. This method is effective for advertising connections to the Internet. For example:
ip route 0.0.0.0 0.0.0.0 x.x.x.x (next hop to the internet)
!
router eigrp 100
redistribute static
default-metric 10000 1 255 1 1500The static route that is redistributed into EIGRP does not have to be to network 0.0.0.0. If you use another network, you must use the ip default-network command to mark the network as a default network. Refer to Configuring a Gateway of Last Resort for further information.
Summarizing to a default route is effective only when you want to provide remote sites with a default route. Since summaries are configured per interface, you do not need to worry about using distribute-lists or other mechanisms to prevent the default route from being propagated toward the core of your network. Note that a summary to 0.0.0.0/0 overrides a default route learned from any other routing protocol. The only way to configure a default route on a router using this method is to configure a static route to 0.0.0.0/0. (Beginning in Cisco IOS Software 12.0(4)T, you can also configure an administrative distance on the end of the summary-address command, so the local summary does not override the 0.0.0.0/0 route).
router eigrp 100
network 10.0.0.0
!
interface serial 0
encapsulation frame-relay
no ip address
!
interface serial 0.1 point-to-point
ip address 10.1.1.1
frame-relay interface-dlci 10
ip summary-address eigrp 100 0.0.0.0 0.0.0.0
***Quote end
More info. here.
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094374.shtml
Hope thie helps.
