Wildcard mask in EIGRP

By | June 8, 2020

The network command in EIGRP uses a classful network as the parameter by default, which means that all interfaces inside the classful network will participate in the EIGRP process. We can enable EIGRP only for specific networks using wildcard masks. The syntax of the command is:

(router-eigrp)#network IP_ADDRESS WILDCARD_MASK

We will use the following example network:

Wildcard mask in EIGRP

The router is directly connected to three subnets. Let’s say that we want to advertise only the 10.0.0.0/24 subnet in EIGRP. We can use the wildcard mask of 0.0.0.255 to do this:

R1(config-router)#network 10.0.0.0 0.0.0.255

Using the show ip protocols command we can verify that only the subnet 10.0.0.0/24 is included in EIGRP:

R1#show ip protocols

Routing Protocol is \"eigrp 1 \" 
Outgoing update filter list for all interfaces is not set 
Incoming update filter list for all interfaces is not set 
Default networks flagged in outgoing updates 
Default networks accepted from incoming updates 
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: eigrp 1
Automatic network summarization is in effect 
Automatic address summarization: 
Maximum path: 4
Routing for Networks: 
10.0.0.0/24
Routing Information Sources: 
Gateway Distance Last Update 
Distance: internal 90 external 170

Notice that 10.0.0.0/24 is listed under the Routing for Networks column. The other two networks (10.0.1.0/24 and 10.0.5.0/24) are not included in EIGRP.

 

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