LAB: EIGRP Summarization with Default routing

Summarization can also be used to originate a default route in EIGRP. The
disadvantage of this configuration however is that all subnets previously
advertised out an interface will be suppressed, since all IPv4 networks are a
subnet of the aggregate 0.0.0.0/0.

R4:
interface Serial0/0.1 point-to-point
ip summary-address eigrp 100 0.0.0.0 0.0.0.0 5
!
interface Serial0/1
ip summary-address eigrp 100 0.0.0.0 0.0.0.0 5

Rack1R5#sho ip route | begin 0.0.0.0/0
D* 0.0.0.0/0 [90/2172416] via 155.1.45.4, 00:02:33, Serial0/1
[90/2172416] via 155.1.0.4, 00:02:33, Serial0/0