Lab 39 - EIGRP Automatic Summarization

Prerequisites: CCNP level skills.

Note!
Use the final configuration used in the Lab 38.

EIGRP (as per CCNP track) offers a plethora of ways to summarize the prefixes:

1. Automatic Summarization.
2. Summarization ('ip summary-address).
3. Summarization with a Default Route.
4. Summarization with a Floating Default Route (floating summary route).
5. Summarization with Administrative Distance 255.
6. Selective Summarization with a Leak Map.

Topology

 Pic. 1 - EIGRP NBMA Topology.

Icons designed by: Andrzej Szoblik - http://www.newo.pl

Task 1

Re-enable automatic summarization (default). Observe the changes in the routing table on all routers.

Task 2
On R2 create a new loopback with the following IP address: 10.0.0.1/16. Enable EIGRP on this interface and check what R3 receives.

Lab Solution

Task 1

Re-enable automatic summarization (default). Observe the changes in the routing table on all routers.

R1, R2 and R3 Configuration:

!

router eigrp 1

 auto-summary

!

Pic. 2 - R1's Routing Table.

Note!
Because I use class A and class B subnets, a discard route is created for both (Null0). Connection between routers uses class A subnet, so the outbound interface is in different class than the loopback subnets being advertised. The result is class B summarization (172.16.0.0).

Task 2
On R2 create a new loopback with the following IP address: 10.0.0.1/16. Enable EIGRP on this interface and check what R3 receives.

R2 Configuration:

!

interface Loopback1
 ip address 10.0.0.1 255.255.0.0
!

router eigrp 1
 network 10.0.0.1 0.0.0.0
 network 10.1.0.2 0.0.0.0
 network 10.1.2.2 0.0.0.0
 network 172.16.102.2 0.0.0.0
 auto-summary
 eigrp router-id 172.16.102.2

!

Verification:

Pic. 3 - R1's EIGRP Routing Table.

Pic. 4- R3's EIGRP Routing Table.

Note!

Because the new IP address belongs to the same class A (10.x.x.x) even though it is subnetted with /16 network mask, EIGRP advertises it out the interface configured with the same class A 10.x.x.x with the CONFIGURED network mask (/16). If it was 11.x.x.x subnet, EIGRP would have summarized it to 11.0.0.0/8.