Passive interface

A passive interface is one that does not send out any routing protocol updates when a routing protocol is configured on a router. The behavior is slightly different for each protocol:

  • EIGRP - The interface does not send out any EIGRP packets (hello, updates, acknowledgments) and does not respond to any received EIGRP packets.
  • OSPF - The interface does not send out any OSPF packets (hello, updates, acknowledgments) and does not respond to any received OSPF packets.
  • RIP - The interface does not send out any RIP updates but does accept and process RIP updates.
  • IS-IS - The interface does not send out any IS-IS packets (hello, link-state PDUs) and does not respond to any received IS-IS packets.

Note:

  • The network on a passive interface will still be advertised if so configured by the routing protocol.
  • BGP does not support the concept of a passive interface, since neighbors are statically configured and are not dynamically learned. If you want to suppress BGP communication, simply don't configure a BGP peering.

The benefits of configuring a passive interface include:

  • Save on bandwidth and CPU usage by eliminating the need to send routing protocol packets to a network segment from which you will never get any replies.
  • Mitigates against malicious users on that particular subnet that may masquerade as a router, creating an adjacency and manipulating the routing of the network.

https://networklessons.com/ospf/ospf-passive-interface https://networklessons.com/cisco/ccna-200-301/rip-passive-interface https://networklessons.com/eigrp/eigrp-passive-interface

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