EIGRP Floating Summarization

R1#
interface FastEthernet0/0
 ip address 12.1.1.1 255.255.255.0
 ip summary-address eigrp 100 0.0.0.0 0.0.0.0 5
 duplex auto
 speed auto
end





Configure a summary default route on R2, which will make the R1 subnets unreachable from R3. R3 is learning default route from R2 summary
A route for 0.0.0.0/0 to the null 0 interface with an administrative distance of 5. When this route is created, it overrides the EIGRP learned default route. Router-R2 will no longer be able to reach destinations that it would normally reach through the 0.0.0.0.0/0 route. 
R2(config)#int f0/1
R2(config-if)#ip summary-address eigrp 100 0.0.0.0 0.0.0.0



We will add the summary route on R2 with AD of 250, R2 learning default route from R1 with AD of 90, so there are two default routes with different ADs and R2 will prefer route with smaller AD and routing table on R3 will be learning the same


R2(config-if)#no ip summary-address eigrp 100 0.0.0.0 0.0.0.0
R2(config-if)#ip summary-address eigrp 100 0.0.0.0 0.0.0.0 250