EIGRP Configuration

Enhaced Interior Gateway Routing Protocol – EIGRP

Its internal administrative distance is 90, and the external one is 170. So that a router configured with EIGRP can exchange information between its neighboring routers, all those routers must be configured with the same process id. Therefore, with this process id, a set of routers is supposedly taken as an autonomous system (AS). However, this is not the correct way of naming it, and only they can exchange routing information among themselves.

Its configuration is as follows:

Router(config)# router eigrp process-id
Router(config-router)# network a.a.a.a
Router(config-router)# network b.b.b.b
Router(config-router)# network c.c.c.c

Where:

• router eigrp.- Command to access router configuration mode by assigning the EIGRP routing protocol.
• process-id.- Process ID must be configured in all routers that share routing information.
• network.- Command used for the router for enable EIGRP packets.
• a.a.a.a – network or host where EIGRP wil be enable

With the above steps, we will have EIGRP working, but by default, when using the network command and a classful network address such as 172.16.0.0.0, all the router interfaces belong to the classful network address will be EIGRP enabled. However, there may be times when the network administrator does not want to include all interfaces within a network when enabling EIGRP.

Use the wildcard-mask option with the network command to configure EIGRP to be enabled only on specific interfaces.  All other parameters have the same function as in the configuration at the beginning.

Your configuration is as follows:

Router(config)# router eigrp id-proceso
Router(config-router)# network a.a.a.a wildcard-mask
Router(config-router)# network b.b.b.b wildcard-mask
Router(config-router)# network c.c.c.c wildcard-mask

Where:

• wildcard-mask – Parameter to specify host or subnets of the interfaces where EIGRP will be enabled.

Wildcard mask determines what bits of the address argument are arbitrary. A wildcard mask bit set to 1 means that the corresponding address bit can be anything. A wildcard mask bit set to 0 means that the corresponding address bit must stay

For example, the network 10.2.2.9 0.0.0.0 means that all bits of 10.2.2.9 matter and enables EIGRP on a single interface, one configured with an IP address 10.2.2.9. By other side, the network 10.2.2.9 0.0.0.255 means ignore the last octet of the address and enables EIGRP on all interfaces configured with addresses in range 10.2.2.1 – 10.2.2.254

How to obtain a wildcard mask:

Given the subnet 172.16.3.0/25, imagine that the wildcard mask is the inverse of a subnet mask or rather the remainder of that mask since from the default subnet mask 255.255.255.255 we will subtract the subnet mask of the network we want to publish, in this case:

 Substract

255.255.255.255----------> Default Mask
255.255.255.128----------> Subnet Mask 172.16.3.0
000.    0.   0. 127----------> Wildcard Mask

Another example: Finding the wildcard mask of 10.1.0.0/16

Substract

255.255.255.255----------> Default Mask
255.255.    0.    0----------> Subnet Mask 10.1.0.0
000.    0.255.255----------> Wildcard Mask

Example

Router(config)# router eigrp 10
Router(config-router)# network 10.1.1.1 0.0.0.0 
Router(config-router)# network 10.99.99.0 0.0.0.255

EIGRP will be enabled on the interface where the host IP 10.1.1.1 is configured. In addition, interfaces that have any IP corresponding to the subnet 10.99.99.0/24.

Verifications Commands

show ip eigrp interfaces [detail] 
show ip protocols 
show ip eigrp neighbors 
show ip eigrp topology [subnet] 
show ip route [eigrp]