Configuring EIGRP Passive Interface in Cisco

Pre-requisite: What is Passive-Interface Command Behavior in RIP, OSPF & EIGRP?

EIGRP Passive Interface is enabled, and the router begins to originate Hello packets and process incoming EIGRP packets on all interfaces that fall within the specified network range. But, this is an unnecessary waste of router resources on logical interfaces such as loopback interfaces as no device will be connected to them and also on interfaces connected to networks with the end hosts that will never have an EIGRP neighborship formed. To prevent wastage of the router resources and CPU utilization, an interface can be configured as a passive interface.

The passive interface neither originates EIGRP packets nor processes them. But the network to which the passive interfacenonpassive is connected will be advertised throughout the routed domain.

EIGRP Passive Interface Configuration Command:

Router EIGRP subcommand	Description	Example
passive-interface <interface interface-id>	To configure an interface as an EIGRP passive interface.	Router(config)#router EIGRP <process-id> Router(config-router)#passive-interface <interface interface-id>
passive-interface default	To configure all interfaces to be passive interfaces leaving a single or a couple of interfaces as nonpassive interface	Router(config)#router EIGRP <process-id> Router(config-router)#passive-interface default Router(config-router)#no passive-interface <interface interface-id>

Configuring EIGRP Passive Interface:

Step 1: Create the 2 router topology in GNS3 as shown in the image below :

Step 2: Configure the IPv4 address on the physical interface on the routers :

R1(config)#interface FastEthernet0/0
R1(config-if)#ip address 10.0.0.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#interface FastEthernet1/0
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#no shutdown

R2(config)#interface FastEthernet0/0
R2(config-if)#ip address 10.0.0.2 255.255.255.0
R2(config-if)#no shutdown

Step 3: Configure a loopback interface on R2 with an IPv4 address :

R2(config)#interface Loopback0
R2(config-if)#ip address 2.2.2.2 255.255.255.255

Step 4: Configure the IPv4 address and default gateway on the VPCS :

PC1> ip 192.168.1.2 /24 192.168.1.1

Step 5: Configuring the EIGRP process on both the routers with the command router eigrp <1-65535> or router eigrp <virtual-Instance Name> and then adding the respective routers’ interface network into EIGRP autonomous system :

R1(config)#router eigrp 1
R1(config-router)#network 192.168.1.0

R1(config-router)#network 10.0.0.0

R2(config-if)#router eigrp 1
R2(config-router)# network 10.0.0.0
R2(config-router)#network 2.2.2.2

Step 6: Checking the IPv4 routing table on the routers to see the EIGRP route entry :

• Entry with the prefix “D” means EIGRP route entry.

R1#show ip route

R2#show ip route

Step 7: Configure R1’s LAN interface (FastEthernet1/0) as a passive interface as it is not connected to an EIGRP-enabled router/MLS and hence doesn’t need to propagate EIGRP packets to VPCS (end-host) :

R1(config)#router eigrp 1
R1(config-router)#passive-interface f1/0
R1(config-router)#exit

Step 8: Verifying passive-interface configuration on R1 with the show command, show ip eigrp interface :

• After configuring the interface (FastEthernet1/0) as a passive interface, it is no longer sending EIGRP packets nor processing any received EIGRP packets in EIGRP autonomous system.

R1#show ip eigrp interface

Step 9: Debugging OSPF hello messages on R1, as it will now only send hello packets through its FastEthernet0/0 (WAN) interface :

R1#debug eigrp packets

To turn off debugging :

R1#undebug all

Step 10: Configure R2’s loopback interface (Loopback0) as a passive interface, as it is a logical interface and no device can be connected to it.

R2(config)#router eigrp 1
    
R2(config-router)#passive-interface loopback0
R2(config-router)#exit

Step 11: Verifying passive-interface configuration on R2 with the show command, show ip eigrp interface :

R2#show ip eigrp interface

Step12: Debugging OSPF hello messages on R2, as R2 will now only send hello packets through its FastEthernet0/0 (WAN) interface :

R2#debug eigrp packets

To turn off debugging : 

R2#undebug all

Step 13: Verifying the connectivity throughout the topology :