OSPF routing Loop?

Discussion in 'Cisco' started by Dave, Aug 13, 2006.

  1. Dave

    Dave Guest

    Hi folks,

    I'm studying for my CCNA and have came accross something which I can't
    understand, it seems I have a routing loop and I thought you can't get
    routing loops with OSPF. I'm using a Boson simulator, here's my

    / \
    Router2 Router3
    \ /

    so here Router 1, Router2 and Router3 connects to switch1,
    Router2,Router3 and Router4 connect to switch2. I was thinking of using
    the 2 routers in the middle of the switches for redundancy.

    PROBLEM: Ping from Router1 cannot see Router4. All interfaces are up.
    If I shutdown the interfaces on Router3 then it works.

    This is me just studying and I'm curious to what commands are available
    to stop this from happening.

    What can I do?

    Dave, Aug 13, 2006
    1. Advertisements

  2. 1. do a trace, to ident where the loop is.
    2. connect to this router and verify the OSPF settings and statics etc.

    could be that some router are not right in OSPF, hence the packets hits the route instead.

    Martin Bilgrav, Aug 13, 2006
    1. Advertisements

  3. Dave

    Dave Guest

    Hi Martin,

    done a trace and it displays something along the lines of...


    there was more lines after 4 but displayed the same thing.

    The only routes inside the router are the OSPF learned routes and the
    directly connected routes.

    I think this is an issue with the Boson simulator, I've came accross
    other strange things re OSPF.

    Dave, Aug 13, 2006
  4. ok, so this IP routes back to the previous one.
    eigther #1 forwards to wrong hext hop, or #2 does - This is what i means.
    There are several commands that you need to get familiar with inorder to
    determine the choise of route in the RTM.
    first is "show ip route"
    This will show you the complete route table. Use this to find the match for
    your destination packet.
    Then you have if its from static or OSPF, and from which neigbour its been
    Drill down this road and you should find the answer.
    If everythin looks fine, then the posibility of simulator software
    errors/"Works as designed"-features exsits.

    Martin Bilgrav, Aug 13, 2006
  5. Dave

    Dave Guest

    hi Martin,

    thanks for your thoughts. It does seem as though the software is at
    fault, 1 router only shows 2 other routers in it's routing table, 1
    router shows 1 router and the another router shows all routes in it's
    routing table. I'll contact Boson and see what they say about it.

    Does this mean that a routing loop shouldn't have occurred here?

    thanks again
    Dave, Aug 14, 2006
  6. Hi,

    It is kinda hard to say, without any config's posted.
    if you could post the running config for all routers, aswell as the output
    of sho ip route for all router.

    Martin Bilgrav, Aug 14, 2006
  7. Dave

    imnobody Guest

    its miight be alil advanced and im not sure if the sim will do it
    but configure one of the links from roter 2 or 3 to router 1 or 4
    as a floating static, meaning set the prioiry of ospf link higher than
    of the primary and it will only use the one link but if it goes down
    the network will
    re converge with the other link automatically
    imnobody, Aug 15, 2006
  8. Dave


    Dec 23, 2012
    Likes Received:
    Boson is not reliable.. You wll get lots of issue and you wll get lost :)
    mprasad079, Dec 30, 2012
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.