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:

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!

hostname R1
!
ip cef
!
interface GigabitEthernet0/1
 ip address 192.168.12.1 255.255.255.0
!
router eigrp 1
 network 192.168.12.0
!
end

hostname R2
!
ip cef
!
interface GigabitEthernet0/1
 ip address 192.168.12.2 255.255.255.0
!
interface GigabitEthernet0/2
 ip address 192.168.23.2 255.255.255.0
!
router eigrp 1
 network 192.168.12.0
 network 192.168.23.0
 eigrp stub connected summary leak-map R3_L0_LEAK
!
ip access-list standard R3_L0
 permit 3.3.3.3
!
route-map R3_L0_LEAK permit 10
 match ip address R3_L0
!
end

hostname R3
!
ip cef
!
interface Loopback0
 ip address 3.3.3.3 255.255.255.255
!
interface Loopback1
 ip address 33.33.33.33 255.255.255.255
!
interface GigabitEthernet0/1
 ip address 192.168.23.3 255.255.255.0
!
router eigrp 1
 network 3.3.3.3 0.0.0.0
 network 33.33.33.33 0.0.0.0
 network 192.168.23.0
!
end

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.