OSPF Passive interface and Configuration
OSPF Passive interface and Configuration
OSPF (Open Shortest Path First) is a routing protocol that establishes routing paths within a network. In an OSPF network, regions are used to organize logically related routers. Ideally, all areas should be physically connected to the backbone (Area 0), which serves as a centralized point for routing information.⭐Related : Top OSPF Protocol Interview Questions and Answers
⭐Related : OSPF protocol : OSPF Packet Types
What is OSPF Passive interface ?
In OSPF routing, a passive interface means the interface is disabled to send the updates to its neighbor - it can received all the routing info but doesn't send updates from the same interface. The purpose is to reducing traffic and potentially improving security. To effectively configure your network's OSPF passive interface, you must first understand how it works.
- Reduced Network Traffic: By not sending hello packets, you save bandwidth and processing power on the router, which is especially beneficial for large networks.
- Improved Security: Passive interfaces keep other routers from detecting the network segment connected to that interface, potentially shielding internal network information from unauthorized devices.
Passive interface Configuration on Router R1
Here is an example using the network diagram where A router in OSPF area 0 and Fa0/1 interface is connected to the internal network. In this example we are going to make interface Fa0/1 as passive interface, so that no routes can be send to the switch connected to the Router R1. Fig 1.1- OSPF Passive Interface
The following configuration enables a passive interface on FastEthernet 0/1 and quickly terminates the neighborship because no Hello is exchanged.
R1>enable
R1# configure terminal
R1(config)# router ospf 1
R1(config-router)# network 10.10.1.0 0.0.0.255 area 0
R1(config-router)# network 10.10.2.0 0 0.0.0.255 area 0
R1(config-router)# passive-interface FastEthernet 0/1
R1(config-router)# exit
R1#
At certain points we can request that a Router do not have neighborship or send hello on any of its interfaces.
In this situation, we no longer need to set each interface to passive. With IOS 12.0 and later, we can now use the passive-interface default command to set all interfaces on a router to passive for a specific protocol.
R1>enable
R1# configure terminal
R1(config)# router ospf 1
R1(config-router)# passive-interface default
R1(config-router)# exit
R1#
- This configuration sets all interfaces on the router to be passive by default for OSPF.
- OSPF won't send hello packets or attempt to form neighbor adjacencies on any interface unless explicitly enabled.
- Network information can still be advertised through other active OSPF interfaces on the router.
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