Routing

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  • 1.  BGP Dual-Home with default route only

    Posted 12-10-2018 13:20

    Hello,

     

    I've been scratching my head for a week as to what is the best solution to my problem.  I haven't found any other discussion on this topic which I think is pretty common:

     

    We have 2 BGP sessions with our upstreams, each announcing a default-route.  If one of the ISP performs an upgrade on their router, BGP goes down and life is good.  However, as their router reloads, the BGP session with us - announcing a default-route - is coming back up before their router as the full table loaded, resulting in a ~30 seconds outage after the BGP neighbor is back up.

     

    ** I depicted the situation as most people would see it, in our case we have an advantage, we are also the upstream provider.

     

    Here are my thought:

     

    1.  Have the upstream (still us in our case) receive the default-route from the internet and propagate it to the customer, in this case the default route wouldn't be generated by the PE, avoiding the blackhole situation on reload

     

    2.  Use a recursive default route with a next-hop of a summary (eg 192.0.2.0/24) from the upstream (e.g. static route 0.0.0.0/0 next-hop 192.0.2.0)

     

    I don't like the first one as it means introducing a default-route in our public ASN.

    I don't like the second one as it still a static route in a fully dynamic environment

     

    What are your thoughts on this?

     


    #BGP
    #default-route
    #dual-home
    #ISP


  • 2.  RE: BGP Dual-Home with default route only
    Best Answer

    Posted 12-10-2018 19:22

    Hello,

    There is always a 3rd option 🙂

    If Your ISP router is from Juniper, then ask Your ISP team to introduce a delay in announcing the 0/0 to You until this ISP router fully converges

    https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/delay-route-advertisements-edit-protocols-group-family-unicast.html

    HTH

    Thx

    Alex