Cisco CCNP - BSCI Exam Tutorial: The Passive Interface Command And OSPF

To pass the BSCI exam and transform a CCNP, you must be conscious of the proper use of passive interfaces. You studied approximately passive interfaces in your CCNA studies, but here we'll review the basic concept and clear up an misconception regarding passive interfaces and OSPF.

Configuring an interface as passive will still allow the interface to receive routing updates, but the interface will no longer transfer them. While the command itself would make you think this command will be applied at the interface level, that is no the circumstance. Below, we'll configure ethernet0 as a RIP passive interface.

R1(config)#router rip

R1(config-router)#passive-interface ethernet0

Ethernet0 ambition no longer send RIP routing updates, yet will accept them.

The passive interface conception is explicit ample with RIP, IGRP, and EIGRP - entire protocols namely send routing update pouches. But OSPF doesn't send routing update parcels - OSPF sends correlate state advertisements. It's the inability of the passive interface mandate to stop LSAs that lead many to think that passive interfaces cannot be secondhand with OSPF.

Even whereas OSPF does not sent "routing updates" in the form that RIP, IGRP, and EIGRP do, you can still configure an OSPF-enabled interface as passive in order to prevent OSPF traffic from exiting or entering that interface. No OSPF adjacency can be formed if one of the interfaces involved is a passive interface, and whether you configure an OSPF-enabled interface as passive where an adjacency already exists, the adjacency will drop about swiftly.

Let's watch that in movement. R1 and R2 have an existing OSPF adjacency over their Ethernet interfaces. In an exertion to decrease routing traffic, R1's e0 interface is configured as passive. The adjacency drips right away.

R1(config)#router ospf 1

R1(config-router)#passive-interface ethernet0

18:31:11: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 above Ethernet0 from FULL apt DOWN, Neighbor Down: Interface down or detached

Knowing how to use the passive interface command is a vital portion of creature a CCNP, and of being a master networker. Good fortune to you in both of these pursuits!