EGRP Configuration

R1(config)# router eigrp 1
R1(config-router)# no auto-summary
R1(config-router)# passive-interface g2/0
R1(config-router)# network 10.0.0.0
R1(config-router)# network 172.16.1.0 0.0.0.15

The AS (Autonomous System) number must match between routers, or they will not form an adjacency and share route information.

Auto-summary might be enabled or disabled by default, depending on the router/IOS version. If it's enabled, disable it.

The network command will assume a classful address if you don't specify the mask.

EIGRP uses a wildcard mask instead of a regular subnet mask.

Wildcard mask

A wildcard mask is basically an 'inverted' subnet mask.

All 1s in the subnet mask are 0 in the equivalent wildcard mask. All 0s in the subnet mask are 1 in the equivalent wildcard mask.

/24	11111111	11111111	11111111	00000000
	255	255	255	255
	00000000	00000000	00000000	11111111

A '0' in the wildcard mask = must match.

A '1' in the wildcard mask = doesn't have to match.

Examples

Example 1

R1 G2/0 IP address:

• 10101100 . 00010000 . 00000001 . 00001110 = 172.16.1.14

EIGRP network command:

• 10101100 . 00010000 . 00000001 . 00000000 = 172.16.1.0

• 00000000 . 00000000 . 00000000 . 00001111 = 0.0.0.15

This means that the first 28 bits must match. They do match, so EIGRP will be activated on the interface.

Example 2

R1 G2/0 IP address:

• 10101100 . 00010000 . 00000001 . 00001110 = 172.16.1.14

EIGRP network command:

• 10101100 . 00010000 . 00000001 . 00000000 = 172.16.1.0

• 00000000 . 00000000 . 00000000 . 00000111 = 0.0.0.7

They do not match, so EIGRP will not be active in G2/0.

Show commands

Router ID

The Router ID order of priority:

1. Manual configuration.

2. Highest IP address on a loopback interface.

3. Highest IP address on a physical interface.