EIGRP Stub Leak Map

The EIGRP stub feature is useful to prevent unnecessary EIGRP queries and to filter some routes that you advertise. What if you want to configure your router as a stub router but still make an exception to some routes that it advertises? That is possible with the leak-map feature. Let’s have a look…

Configuration

Here is the topology we will use:

three routers r1 r2 r3

R3 has two loopback interfaces that we advertise in EIGRP. R2 will become our stub router, which prevents R1 from learning 3.3.3.3/32 and 33.33.33.33/32. We’ll then use the leak-map so that R2 makes an exception, allowing R1 to learn 3.3.3.3/32.

Let’s start with a basic EIGRP configuration:

R1(config-if)#router eigrp 1
R1(config-router)#network 192.168.12.0

R2(config-if)#router eigrp 1
R2(config-router)#network 192.168.12.0
R2(config-router)#network 192.168.23.0

R3(config-if)#router eigrp 1
R3(config-router)#network 192.168.23.0
R3(config-router)#network 3.3.3.3 0.0.0.0 
R3(config-router)#network 33.33.33.33 0.0.0.0

Right now, R1 can learn about the 3.3.3.3/32 and 33.33.33.33/32 networks:

R1#show ip route eigrp 
      3.0.0.0/32 is subnetted, 1 subnets
D        3.3.3.3 [90/131072] via 192.168.12.2, 00:00:10, GigabitEthernet0/1
      33.0.0.0/32 is subnetted, 1 subnets
D        33.33.33.33 
           [90/131072] via 192.168.12.2, 00:00:10, GigabitEthernet0/1
D     192.168.23.0/24 [90/3072] via 192.168.12.2, 00:00:12, GigabitEthernet0/1

Let’s turn R2 into a stub router:

R2(config-if)#router eigrp 1
R2(config-router)#eigrp stub

The default option for a stub router is that it only advertises connected and summary routes. That’s why R1 is now unable to learn the networks from R3:

R1#show ip route eigrp 
D     192.168.23.0/24 [90/3072] via 192.168.12.2, 00:00:14, GigabitEthernet0/1

If we want to make an exception to this rule, we can use a leak-map. I’ll create an access-list that matches 3.3.3.3/32 and add it to a route-map. The route-map can then be used in the eigrp stub command:

R2(config)#ip access-list standard R3_L0
R2(config-std-nacl)#permit host 3.3.3.3
R2(config)#route-map R3_L0_LEAK
R2(config-route-map)#match ip address R3_L0
R2(config)#router eigrp 1
R2(config-router)#eigrp stub leak-map R3_L0_LEAK

Let’s check R1 to see the new result:

R1#show ip route eigrp 
      3.0.0.0/32 is subnetted, 1 subnets
D        3.3.3.3 [90/131072] via 192.168.12.2, 00:00:14, GigabitEthernet0/1
D     192.168.23.0/24 [90/3072] via 192.168.12.2, 00:00:16, GigabitEthernet0/1

There we go, R2 now advertises 3.3.3.3/32 because of leak-map. That’s all there is to it!

Configurations
R1
R2
R3

Want to take a look for yourself? Here you will find the final configuration of each device.

Conclusion

You have now learned how to make an exception in the routers that an EIGRP stub router advertises by using the leak-map feature.

Table of Content

Unit 1: Introduction to EIGRP

Unit 2: EIGRP Neighbor Adjacency

Unit 3: EIGRP Filtering

Unit 4: EIGRP Advanced Features