Lesson Contents
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!
Configurations
Want to take a look for yourself? Here you will find the final configuration of each device.
R1
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
R2
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
R3
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.