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Forum Replies

  1. Technically, you can advertise whatever you want in BGP but in reality, it's not going to happen.

    Let's say you are connected to ISP1 and ISP2 and connected through BGP to learn some prefixes from them. If you don't have any address space of your own, they will probably not accept anything that you do try to advertise by filtering everything inbound. If not, you could end up becoming a transit AS since you might advertise address space from ISP1 to ISP2 and vice versa.

    Even if they do accept some prefixes that you advertise, you would be advertising address space that doesn't belong to you. If you want a good example, here's how Pakistan knocked Youtube of the Internet :wink:

  2. Hi @kayoutoure

    When we are talking about a BGP free core in MPLS networks, we are talking about the P routers:

    The PE routers are running BGP.

    If you are still a little fuzzy on BGP / IBGP, I would recommend to stay away from MPLS VPN for now since it’ll only be even more confusing :smile:

    The best way to see IBGP split horizon in action, is to test it with three routers:


    Configure IBGP between R1-R2 and R2-R3 but not between R1 and R3. Now add a loopback on each router and advertise it in BGP…then check your routing tables :wink:

  3. Thanks for the long discussion, Rene.

    Yeap ! I will keep doing simple labs, until I get a better understanding of adavanced stuff, like BGP FREE CORE, SPLIT HORIZON, MPLS VPN, … :smile:

  4. How is it that R5 router has a route in it for yet it cannot ping that same IP. I am more curious how R5 is getting the route than the ping issue I understand why we cannot ping

    I also just now noticed you only configured EBGP between R4 and R5 why you would configure EBGP between R4 and R5 and not configure it between R1 and R2. Was that just over looked?

    Watched some videos tonight picked up a couple things I either missed or had not gotten to yet.

    1. if routers in the same AS and connected they use IBGP
    2. If routers in different AS and connected they use EBGP


  5. lee says:

    Hi Rene,

    When the lab is completed I run a show ip route and the command output shows the admin distance of bgp (120) why is the next answer listed as 0?



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