Prerequisites: CCNP level skills.
EIGRP (as per CCNP track) offers a plethora of ways to summarize the prefixes:
Pic. 1 - EIGRP NBMA Topology.
Icons designed by: Andrzej Szoblik - http://www.newo.pl
Task 1
EIGRP is running on all interfaces of all routers shown in the topology (pic. 1). Check R3's EIGRP routing table. On R2 summarize all EIGRP prefixes so that EIGRP on R1 receives only a default route from R2. On R1 check the reachability to 192.168.2.2 and 192.168.3.2.
Task 2
On R1 summarize all EIGRP perfixes so that EIGRP on R3 receives only a default route from R1. On R3 check the reachability to 192.168.2.2 and 192.168.3.2. In case of problems fix the issue but do not remove the summarization on R1 and R2.
Lab Solution
Task 1
EIGRP is running on all interfaces of all routers shown in the topology (pic. 1). Check R3's EIGRP routing table. On R2 summarize all EIGRP prefixes so that EIGRP on R1 receives only a default route from R2. On R1 check the reachability to 192.168.2.2 and 192.168.3.2.
R2 Configuration:
!
interface FastEthernet1/0
ip address 10.1.12.2 255.255.255.0
ip summary-address eigrp 1 0.0.0.0 0.0.0.0 5
ip address 10.1.12.2 255.255.255.0
ip summary-address eigrp 1 0.0.0.0 0.0.0.0 5
!
Verification:
Pic. 2 - R1's Routing Table.
Obviously ping from both R1 and R3 towards 192.168.2.2 and 192.168.3.2 works.
Task 2
On R1 summarize all EIGRP perfixes so that EIGRP on R3 receives only a default route from R1. On R3 check the reachability to 192.168.2.2 and 192.168.3.2. In case of problems fix the issue but do not remove the summarization on R1 and R2.
R1 Configuration:
!
interface Serial0/1
ip address 10.1.13.1 255.255.255.0
ip summary-address eigrp 1 0.0.0.0 0.0.0.0 5
ip address 10.1.13.1 255.255.255.0
ip summary-address eigrp 1 0.0.0.0 0.0.0.0 5
!
Pic. 3 - R1's Routing Table.
Analogous to the previous post (lab 42). R1's summary route (the discard route) overrides the default route sent by R2 (summary route to Null0 has distance 5, R2's advertising default route with distance 90). This results in losing access to R2's Loopbacks on both R1 and R3.
Solution first was presented in lab 42. The second option is to use Distance 255 for the summary route on R1. The Administrative Distance 255 is not a candidate for route installation in the routing table. The order of operation matters: first remove the previous setting and configure new one with AD 255.
R1 Configuration:
!
R1(config-if)#no ip summary-address eigrp 1 0.0.0.0 0.0.0.0 5
R1(config-if)#ip summary-address eigrp 1 0.0.0.0 0.0.0.0 255
R1(config-if)#ip summary-address eigrp 1 0.0.0.0 0.0.0.0 255
!
Note!
The same way I can summarize any prefixes and add distance 255. The result: a discard route is not placed in the routing table.