Lab Objective
Reconfigure EIGRP on a router with multiple interfaces using precise wildcard masks in the network command, verifying only the intended interfaces participate in EIGRP rather than every interface within the same classful network.
Lab Purpose
The basic EIGRP configuration in the previous lab used the classful major network address alone, which enables EIGRP on every interface falling within that broad range. A precise wildcard mask, discussed earlier in this series regarding ACLs, narrows this to exactly the intended subnet, avoiding accidentally enabling EIGRP on an interface that should remain excluded.
Lab Topology
R1 with three interfaces, all within the
10.0.0.0/8 classful range:
Gi0/0: 10.1.1.1/24 (should participate in EIGRP)
Gi0/1: 10.1.2.1/24 (should participate in EIGRP)
Gi0/2: 10.99.99.1/24 (management-only, should
NOT participate in EIGRP)Task 1: Configure the Three Interfaces
Configure all three interfaces with the addresses shown.
Task 2: Enable EIGRP Using a Broad Network Statement (Demonstrating the Problem)
Configure EIGRP using only network 10.0.0.0 with no wildcard mask, and observe that all three interfaces become EIGRP-enabled, including the unintended management interface.
Task 3: Remove the Broad Statement and Use Precise Wildcard Masks
Remove the broad network statement, then add two precise network statements using wildcard masks that match only Gi0/0 and Gi0/1's specific subnets.
Task 4: Verify Only the Intended Interfaces Participate
Confirm EIGRP is now active only on Gi0/0 and Gi0/1, and Gi0/2 no longer participates.
Solution and Verification
R1(config)# interface gigabitethernet0/0
R1(config-if)# ip address 10.1.1.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface gigabitethernet0/1
R1(config-if)# ip address 10.1.2.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface gigabitethernet0/2
R1(config-if)# ip address 10.99.99.1 255.255.255.0
R1(config-if)# no shutdownR1(config)# router eigrp 100
R1(config-router)# network 10.0.0.0
R1# show ip eigrp interfaces
Interface Peers Xmit Queue
Gi0/0 0 0/0
Gi0/1 0 0/0
Gi0/2 0 0/0
-- All three interfaces are EIGRP-enabled,
-- including Gi0/2, which was never intended
-- to run a routing protocol at allR1(config)# router eigrp 100
R1(config-router)# no network 10.0.0.0
R1(config-router)# network 10.1.1.0 0.0.0.255
R1(config-router)# network 10.1.2.0 0.0.0.255R1# show ip eigrp interfaces
Interface Peers Xmit Queue
Gi0/0 0 0/0
Gi0/1 0 0/0
-- Gi0/2 no longer appears -- EIGRP is now
-- precisely scoped to only the intended
-- subnetsKey Takeaway
A wildcard mask in the EIGRP network command narrows participation to exactly the specified subnet, rather than the entire classful network the address belongs to — this precision matters specifically on routers with a mix of interfaces that should and should not run the routing protocol, such as a dedicated management interface that must never form neighbor relationships.