EIGRP Poisoned Floating Summarization

Routes with an administrative distance of 255 are not candidates to be installed in the routing table. By poisoning the interface-level summary on R5 with a distance of 255, the route to Null0 cannot be installed locally in the routing table, but the summary itself can be advertised out the interface.

R2#router eigrp 100
 summary-metric 0.0.0.0/0 distance 255

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

EIGRP Summarization with Leak Map

Routes matched in the leak-map route-map will be advertised in addition to the summary.

#eigrp stub receive-only, the eigrp stub command is issued with the receive-only keyword to configure the device as a receive-only neighbor (connected, summary, and static routes will not be sent)

R2(config)#ip access-list extended LEAK
R2(config-ext-nacl)#permit ip 2.2.2.0 0.0.0.255 any

R2(config)#route-map LEAK-MAP 10
R2(config-route-map)#match ip address LEAK
 
R2(config)#int f0/0
R2(config-if)#ip summary-address eigrp 100 0.0.0.0 0.0.0.0 leak-map LEAK-MAP









When summaries are created in EIGRP, OSPF, and BGP, the router automatically
installs a route to Null0 to match the summary. This is used to prevent the router
from forwarding traffic for destinations inside the summary that it does not have a
longer match for