Passive-Interface Command on CISCO Router/Switch

Command

Passive-Interface Default

Use

This command prevents EIGRP from forming adjacencies on specified interfaces on the router. Using no passive-interface default will allow EIGRP communication.

Syntax

Router(config-router)#passive-interface <interface>

Example

In this example, we will use passive-interface default to block all EIGRP adjacencies. Then we will allow communication through R2’s Fa0/0

R2(config)#do show ip route eigrp
1.0.0.0/32 is subnetted, 3 subnets
D 1.1.1.1 [90/156160] via 10.1.1.1, 00:49:20, FastEthernet0/0
D 1.3.3.3 [90/156160] via 10.1.1.1, 00:49:20, FastEthernet0/0
D 1.2.2.2 [90/156160] via 10.1.1.1, 00:49:20, FastEthernet0/0
192.168.13.0/30 is subnetted, 1 subnets
D 192.168.13.0 [90/2172416] via 10.2.2.3, 00:49:22, FastEthernet1/0
[90/2172416] via 10.1.1.1, 00:49:22, FastEthernet0/0
33.0.0.0/32 is subnetted, 1 subnets
D 33.33.33.33 [90/156160] via 10.2.2.3, 00:49:22, FastEthernet1/0
3.0.0.0/32 is subnetted, 1 subnets
D 3.3.3.3 [90/156160] via 10.2.2.3, 00:49:22, FastEthernet1/0
111.0.0.0/32 is subnetted, 1 subnets
D 111.111.111.111 [90/156160] via 10.1.1.1, 00:49:20, FastEthernet0/0
10.0.0.0/24 is subnetted, 3 subnets
D 10.4.4.0 [90/2172416] via 10.2.2.3, 00:50:57, FastEthernet1/0
[90/2172416] via 10.1.1.1, 00:50:57, FastEthernet0/0
11.0.0.0/32 is subnetted, 1 subnets
D 11.11.11.11 [90/156160] via 10.1.1.1, 00:49:20, FastEthernet0/0
133.133.0.0/32 is subnetted, 1 subnets
D 133.133.133.133 [90/156160] via 10.2.2.3, 00:49:22, FastEthernet1/0

Here we enable passive-interface default on R2.

R2(config)#router eigrp 100
R2(config-router)#passive-interface default
R2(config-router)#
*Mar 1 01:06:46.775: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.1.1 (FastEthernet0/0) is down: interface passive
*Mar 1 01:06:46.799: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.2.2.3 (FastEthernet1/0) is down: interface passive
R2(config-router)#

We can see there are no longer any EIGRP routes on R2.

R2(config-router)#do show ip route eigrp

R2(config-router)#

Now we will use no passive-interface fa0/0 to allow communication through R2’s Fa0/0

R2(config)#router eigrp 100
R2(config-router)#no passive-interface fa0/0
R2(config-router)#
*Mar 1 01:07:55.815: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.1.1 (FastEthernet0/0) is up: new adjacency
R2(config-router)#

After that, we have routes coming in from Fa0/0 but not any other interface.

R2(config)#do show ip route eigrp
1.0.0.0/32 is subnetted, 3 subnets
D 1.1.1.1 [90/156160] via 10.1.1.1, 00:01:06, FastEthernet0/0
D 1.3.3.3 [90/156160] via 10.1.1.1, 00:01:06, FastEthernet0/0
D 1.2.2.2 [90/156160] via 10.1.1.1, 00:01:06, FastEthernet0/0
192.168.13.0/30 is subnetted, 1 subnets
D 192.168.13.0 [90/2172416] via 10.1.1.1, 00:01:06, FastEthernet0/0
33.0.0.0/32 is subnetted, 1 subnets
D 33.33.33.33 [90/2300416] via 10.1.1.1, 00:01:06, FastEthernet0/0
3.0.0.0/32 is subnetted, 1 subnets
D 3.3.3.3 [90/2300416] via 10.1.1.1, 00:01:06, FastEthernet0/0
111.0.0.0/32 is subnetted, 1 subnets
D 111.111.111.111 [90/156160] via 10.1.1.1, 00:01:06, FastEthernet0/0
10.0.0.0/24 is subnetted, 3 subnets
D 10.4.4.0 [90/2172416] via 10.1.1.1, 00:01:06, FastEthernet0/0
11.0.0.0/32 is subnetted, 1 subnets
D 11.11.11.11 [90/156160] via 10.1.1.1, 00:01:06, FastEthernet0/0
133.133.0.0/32 is subnetted, 1 subnets
D 133.133.133.133 [90/2300416] via 10.1.1.1, 00:01:06, FastEthernet0/0

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