Routing

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Ask questions and share experiences about ACX Series, CTP Series, MX Series, PTX Series, SSR Series, JRR Series, and all things routing, including portfolios and protocols.
  • 1.  What is right way to prevent GRE tunnel flapping ?

    Posted 03-05-2021 23:36
    If the GRE tunnel end points have multiple links,  both tunnel points reach each other via dynamic routing protocols. The tunnels will flap.  What is the right way to prevent this ?

    In the Juniper training,  it adds static routes.  But the training does not say why. 

    Anyone can tell why ? 

    Currently I am doing a GRE lab, even I added static routes, the GRE tunnel still flaps.

    thanks in advance !!


  • 2.  RE: What is right way to prevent GRE tunnel flapping ?

    Posted 03-06-2021 11:20
    I noticed the GRE tunnel stayed stable after I removed ospf3 over GRE tunnel.  That made me think the flapping was caused by ospf3 over the tunnel.
    Then I added OSPF3 back and changed hello-interval from 10 to 30, it seemed to alleviate tunnel flapping.

    Anyone can teach me  what reason behind this ?
    Is this similar to Cisco why Frame Relay has 30s by default vs. broadcast network 10s by default ?

    thanks a lot !!



  • 3.  RE: What is right way to prevent GRE tunnel flapping ?
    Best Answer

    Posted 03-06-2021 20:10
    If the tunnel endpoints are learned via the tunnel itself, the tunnel goes down. 

    Here is an example with IPSEC, but it is the same problem with GRE.  


    To solve it, make sure that the metric of the tunnel is higher than the metric of the path via the physical interface, OR configure static routing to reach the tunnel end points. 

    Regards, 
     ​


  • 4.  RE: What is right way to prevent GRE tunnel flapping ?

    Posted 03-06-2021 21:16
    thanks a million for coaching !!!


  • 5.  RE: What is right way to prevent GRE tunnel flapping ?

    Posted 03-06-2021 21:19
    My pleasure! Keep working hard!


  • 6.  RE: What is right way to prevent GRE tunnel flapping ?

    Posted 03-06-2021 21:20
    I used static route to have the GRE much stable.

    thanks !!