passive-interface [intf]
Prevents an interface from sending EIGRP hello packets and forming neighbor adjacencies, while still allowing the router to advertise the subnet of that interface in EIGRP updates.
passive-interface [intf]When to Use This Command
- On a LAN interface where no other EIGRP routers exist, to reduce unnecessary multicast hello traffic.
- On a loopback interface to advertise its subnet without forming a neighbor relationship.
- On a WAN interface connected to a non-EIGRP device, to avoid sending hellos and wasting bandwidth.
- On a management interface that should be reachable via EIGRP but should not participate in neighbor discovery.
Command Examples
Making a single interface passive
router eigrp 100
passive-interface GigabitEthernet0/1R1(config-router)# passive-interface GigabitEthernet0/1 R1(config-router)#
The command is entered under router configuration mode. No output is shown upon success; the interface is now passive.
Making all interfaces passive and then enabling specific ones
router eigrp 100
passive-interface default
no passive-interface GigabitEthernet0/0R1(config-router)# passive-interface default R1(config-router)# no passive-interface GigabitEthernet0/0 R1(config-router)#
First, all interfaces are set passive. Then, GigabitEthernet0/0 is removed from passive mode, allowing it to send hellos and form adjacencies.
Understanding the Output
The passive-interface command does not produce any output when executed successfully. To verify which interfaces are passive, use 'show ip eigrp interfaces'. In the output, look for the 'Passive' column: 'Yes' means the interface is passive (no hellos sent, no neighbors formed), 'No' means it is active. Also, 'show ip eigrp neighbors' will not show any neighbors learned via passive interfaces. If you expect a neighbor but don't see it, check if the interface is accidentally passive.
CCNA Exam Tips
Remember that passive interfaces still advertise their subnet in EIGRP updates; they just don't send hellos or form neighbors.
The 'passive-interface default' command makes all interfaces passive, then you use 'no passive-interface' to enable specific ones.
On the CCNA exam, you might be asked to configure EIGRP on a router with multiple interfaces, but only one should form a neighbor adjacency.
Passive interfaces reduce unnecessary traffic and improve security by not exposing EIGRP to untrusted networks.
Common Mistakes
Mistake: Applying passive-interface to an interface that should form a neighbor adjacency, causing no neighbor relationship to form.
Mistake: Forgetting that passive interfaces still advertise the network, which can lead to routing loops if the subnet is not actually reachable.
Mistake: Using 'passive-interface default' and then forgetting to enable the necessary interfaces, resulting in no EIGRP adjacencies at all.
Related Commands
show ip eigrp interfaces
Displays detailed information about interfaces on which EIGRP is enabled, including neighbor status, pending routes, and interface statistics, used to verify EIGRP adjacency and interface participation.
show ip eigrp neighbors
Displays the neighbor table for EIGRP, showing all directly connected EIGRP routers and their status, used to verify EIGRP adjacencies and troubleshoot neighbor relationships.
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