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Forum Replies

  1. aujla3 says:

    hay rene, is there any way to make the default as passive and yet keep the interface that already has a neighbour as non passive? in other words is there a way to change the default on the router to passive on all interfaces except the onces that already have neighbours, without dropping the adj.

    Thanks,

  2. Hi Kam,

    I'm afraid not, if you use the global passive command then it will kill any OSPF neighbor adjacencies that you have...unless you do "no passive interface" for these interfaces.

    Rene

  3. Hi Adil,

    If you use passive-interface default then all interfaces will be passive. If you want to disable it for fa0/0 then you can use the no passive-interface fa0/0 command under the OSPF process.

    Rene

  4. Hi Ivaylo,

    It won't prevent us from receiving the hello packets but I believe it does stop processing them. Here's a little experiment I did with two routers, directly connected to each other:

    R1#debug ip ospf hello 
    OSPF hello debugging is on

    Now we can see we are sending and receiving hello packets:

    R1#
    OSPF-1 HELLO Gi0/1: Send hello to 224.0.0.5 area 0 from 192.168.12.1
    OSPF-1 HELLO Gi0/1: Rcv hello from 2.2.2.2 area 0 192.168.12.2

    Let's make the interface passive:

    R1(config)#router ospf 1
    R1(config-router)#passive-interface GigabitEthernet 0/1

    At this moment my debug is not producing any output anymore. Basically OSPF has been disabled on the interface. We are still receiving packets though:

    R1#debug ip packet 
    IP packet debugging is on

    R1#
    IP: s=192.168.12.2 (GigabitEthernet0/1), d=224.0.0.5, len 80, rcvd 0
    IP: s=192.168.12.2 (GigabitEthernet0/1), d=224.0.0.5, len 80, input feature, packet consumed, MCI Check(109), rtype 0, forus FALSE, sendself FALSE, mtu 0, fwdchk FALSE

    Above you can see that we are receiving OSPF packets from 192.168.12.2.

    About your other question:

    OSPF as an IGP (Interior Gateway Protocol) is typically used on our "own" networks. If you have a connection to your ISP for Internet access then all you need is a default route to them...we don't run OSPF with the ISP.

    Hope this helps!

    Rene

  5. Hi Ahmad,

    OSPF and EIGRP have one thing in common, they both establish a neighbor adjacency before they advertise any routing information. RIP doesn't establish a neighbor adjacency, it just advertises routing updates.

    When you use the passive interface command for RIP then it stops advertising RIP routing updates on that interface. When you use it for OSPF or EIGRP, they won't send any hello packets anymore so that it becomes impossible to establish a neighbor adjacency on the passive interface.

    Rene

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