Passive-interface command behavior in RIP, EIGRP & OSPF

July 12th, 2008 Wael Osama Posted in EIGRP, IGP, OSPF, RIP | 18 Comments »

Passive-interface command is used in all routing protocols to disable sending updates out from a specific interface. However the command behavior varies from o­ne protocol to another.

In RIP this command will disable sending multicast updates via a specific interface but will allow listening to incoming updates from other RIP speaking neighbors.

This simply means that the router will still be able to receive updates o­n that passive interface and use them in the routing table.

In EIGRP the passive-interface command stops sending outgoing hello packets, hence the router can not form any neighbor relationship via the passive interface. This behavior stops both outgoing and incoming routing updates.

In OSPF the passive-interface has a similar behavior to EIGRP. The command suppresses hello packets and hence neighbor relationships.

I have o­nly o­ne final note here regarding sending unicast updates:

If you used the neighbor command under the RIP process, the router will send unicast updates as well as multicast updates.The passive-interface command must be used disable multicast updates and allowing o­nly unicast.

In EIGRP the neighbor command disables multicast updates o­n an interface by default and allows o­nly unicast updates.


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18 Responses to “Passive-interface command behavior in RIP, EIGRP & OSPF”

  1. Passive-interface command behavior in RIP, EIGRP & OSPF « Pete’s Packet Says:
    June 6th, 2009 at 3:30 am

    [...] Posted by Peter Kurdziel on June 5, 2009 Passive-interface command behavior in RIP, EIGRP & OSPF [...]

  2. Ripduman singh Says:
    July 13th, 2009 at 10:34 pm

    quite simple yet stronger and knowledgable tutorials.thx.

  3. Wael Osama Says:
    July 13th, 2009 at 10:50 pm

    @Ripduman
    I am glad we are meeting you expectations :) , your feedback is really appreciated.

  4. Jesicbz Says:
    September 2nd, 2009 at 2:06 pm

    Thank you so much for the useful info. Still I would like to know what is the difference between interface shut down and passive behavior in EIGRP & OSPF (My understanding is we can shut down the interface rather it configured as passive. Is any other advantage as being passive interface than it could be shut down). I am very much thankfull for your response.

  5. Wael Osama Says:
    September 3rd, 2009 at 7:35 pm

    Jescibz,

    If you shutdown the interface it will not be advertised by any routing protocol, the main reason behind using the passive interface command is to be able to advertise the interface subnet without forming adjacency on that interface.

    If you still need more clarifications feel free to post your thoughts.

    Wael

  6. ilkin Says:
    January 21st, 2010 at 4:50 pm

    Hi everybody,
    I have a similar question with Jescibz. I do not understand what is the difference between two interfaces that one of them is “passive interface” on eigrp, and the other one is not enabled for eigrp(do not send any Hello packets but not shutdown also)

    We can do the same thing that “passive interface” command does by not enabling eigrp on this interface. Am I right?

    Thanks…

  7. Wael Osama Says:
    January 24th, 2010 at 2:39 pm

    ilkin,

    passive interface advertise the network defined on this interface without participating in neighbor relationship on the interface; without passive interface the network defined on this interface will not be advertised.

  8. some guy Says:
    April 28th, 2010 at 5:42 am

    what’s the benefit of not forming an adjacency?

  9. abc Says:
    May 4th, 2010 at 5:28 pm

    thanks

  10. Khan Says:
    September 16th, 2010 at 10:55 am

    Hi Wael,

    Just to quickly summarize the above,

    Say if we have three interfaces Fa0, Fa1 and Fa2, on a router running EIGRP/OSPF, considering in mind that these are interface specific protocols, meaning that we would use the network statement only if its present as a directly connected network to our router.

    I go ahead and use the command passive-interface default and then in the next line i write no passive-interface Fa0, Im assuming that Fa0 is only interface now which can establish eigrp neighbors?? Will the network of Fa1 and Fa2 be learnt by the neighbors?????

    By the way excellent posts – asusual :)

  11. Wael Osama Says:
    September 16th, 2010 at 11:33 pm

    Hi Khan,

    Your summary is exactly right :)

    Thanks for your decent comment and please feel free to ask, request or comment anytime

  12. Khan Says:
    September 17th, 2010 at 3:46 am

    Hi Wael,

    Thanks for replying.

    Request you to please clarify the below:

    I go ahead and use the command passive-interface default and then in the next line i write no passive-interface Fa0, Im assuming that Fa0 is only interface now which can establish eigrp neighbors?? Will the network of Fa1 and Fa2 be learnt by the neighbors?????

    The last part is eating my brains.. Will the eigrp/ospf neighbor know about the Fa1 and Fa2 networks?

    Sorry to bug you, hope to see a reply soon :)

  13. Wael Osama Says:
    September 17th, 2010 at 2:45 pm

    Hi Khan,

    My answer to this is yes, these networks will be advertised to other EIGRP/OSPF neighbors.

  14. Shank Says:
    November 12th, 2010 at 4:36 am

    Hello Everyone,

    I was going through this post for my query . I understood that On passive interface the neighbors do not form adjacency but network are advertised. Why do the networks get advertise if it is a passive interface? In case of EIGRP, the Cisco document says that it does not advertise or receive packets /updates on that interface which is configured as passive. In my lab i had configured 3 routers with all the LAN interface as passive. I still got the routes of the lan on other routers from the respective Serial connections. Does Update not include network route update from the interface ? Its a bit confusing.

  15. Syed Says:
    February 12th, 2011 at 10:45 am

    Dear Shank,

    Just saw your post above and want to clarify your queries, Yes the updates are not sent on a passive interface but since you have advertised the subnets under the routing process that is why you will see those subnets in your routing table. If you still have some concerns please feel free to contact me on syedasifraza1@gmail.com

  16. Roshan Biswakarma Says:
    February 23rd, 2011 at 8:14 am

    Hi , as per the cisco document it says passive interface in Eigrp can be advertise its interface though it is not forming any neighbour relationship. it is true right? because i saw in above explanation that passive interface in eigrp wont participate in incoming or outgoing routing updates.

  17. Wael Osama Says:
    February 23rd, 2011 at 1:21 pm

    Hi Roshan,

    your understanding is correct, however it means the interface will be included in routing updates sent via other active EIGRP interfaces which have neighbors formed. Passive interfaces will not send or process any updates because there is no neighbors to send to or receive from.

  18. anu Says:
    July 8th, 2011 at 5:02 am

    “In EIGRP the passive-interface command stops sending outgoing hello packets, hence the router can not form any neighbor relationship via the passive interface. This behavior stops both outgoing and incoming routing updates”

    This indicates that genereally two routers wont advertise or send updates unless they form neighbour ship,But here as they not forming any neighbhour ship how can they caommunicate they cant rit? i saw a post (Wael Osama told that the passive interface command is to be able to advertise the interface subnet without forming adjacency on that interface how ?) what is the purpose of making that as passive interfcae instead of shut down.

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