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RE: Use of generated routes

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  • 1.  RE: Use of generated routes

    Posted 05-03-2020 12:40
    We are currently receiving full route table (along with the default route) from the Internet in both of our edge routers that have separate independent BGP peering with the ISP. 
    In this scenario, would it make sense to configure a generated default route and advertise the default router to our downstream routers or would it be better to just "match on protocol bgp, route-filter 0/0" and advertise this policy as export to our internal routers using OSPF. We are not running IBGP internally, so have rely to OSPF.
    I am leaning towards the later option, since I don't have to create generated routes and etc. Can somebody please advise on this setup? 
    Thanks in Advance.

  • 2.  RE: RE: Use of generated routes

    Posted 05-03-2020 18:55

    Hey biraj,


    Greetings, I will also lean to the second option, if you want to go even further, you can create a policy to have only your BGP routes as contributing routes for that generate route, and  if those BGP routes are gone, you will stop advertizing that default route so you would not have your traffic blackholed or sent to another next hop if you don't have a route to the ISP


    If this solves your problem, please mark this post as "Accepted Solution" so we can help others too \:)/



    Lil Dexx
    JNCIE-ENT#863, 3X JNCIP-[SP-ENT-DC], 4X JNCIA [cloud-DevOps-Junos-Design], Champions Ingenius, SSYB



  • 3.  RE: RE: Use of generated routes
    Best Answer

    Posted 05-03-2020 20:33



    If You receive 0/0 and ::/0 from Your ISP, You don't need to bother about generated routes.

    Generally speaking, creating 0/0 generated route is more pain than it's worth because with incessant BGP route churn in the wider internet, JUNOS RPD is going to be constantly reevaluating contributors (something like 800K contributors!) and reselecting the best numerically lowest contributor to make this contributor' nexthop the generated route' nexthop.

    Ditto for ::/0 generated route, albeit with lesser contributors but they are growing.


    @biraj wrote:
    We are not running IBGP internally, so have rely to OSPF.


    This is a MAJOR disadvantage because without iBGP, You can only run internet in GRT and LDP-based MPLS services such as LDP VPLS and L2circuits. And that's all.

    All other services (L3VPN, L2VPN, EVPN, flowspec etc) use BGP so I'd say start planning for iBGP before Your network grows large.






  • 4.  RE: RE: Use of generated routes

    Posted 05-04-2020 19:51

    I am in full agreement with you regarding running IBGP internally as well. Currently doing some investigative work towards the edge of the network for the customer, so as to propose a better solution, as I have a full grasp of the existing setup. Thanks to you and Dex for feedback. There is always something new to learn here.