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Notable Replies

  1. Hi Rene, i am confused to understanding this concept. please help.

    So what I could figure-out so far is :-

    "In a transit AS scenario, Enabling BGP sync made sense. because otherwise our ASBR router will advertise EBGP routes (learned from EBGP neighbor) to other internal routers as well and ultimately may become a transit AS for both EBGP neighbors which we don't want.

    So the rule said if we learn a route from IGP then only we should advertise it to other EBGP neighbor. that means we are only advertising network that we own.
    But now this rule is not needed in today's scenario. .....why ?(please help me in understanding)

  2. Hi Abhishek,

    BGP synchronization is an old rule in a time where not all routers within the AS were running IBGP. The problem here is not that we don't want to become a transit AS, but that R5 is learning a route that it can't reach (because R3 will drop the traffic).

    By enabling synchronization, we will not advertise this network to R5 anymore which might be a better idea compared to advertising something that is unreachable. Only once the route is known in the IGP, we know that R3 will be able to forward the traffic and only then we will advertise the route to R5.

    We don't use this anymore since nowadays, we run IBGP on all our routers if we have a transit AS, or even better...we use MPLS VPN where we only require BGP between the PE routers.

    Hope this helps!

    Rene

  3. Awesome work Rene!!!

  4. Rene,

    on router 4 you type a "show ip bgp" and say that the "router will install the OSPF (AD 110) entry for 1.1.1.0/24
    instead of IBGP (AD 200) route"

    router 4's BGP table says that LocPrf is 100. did you mean t6o say ad 100 and not ad110 ? if i have this wrong can you explain what the "LocPrf" as I think that it means the local preference of iBGP AS2

    thank you

  5. Hi @chriscowboyfann,

    I didn't watch the video again but if I was talking about the AD, it's 110 for OSPF. If the router has to decide if it wants to use routing information from routing protocol X or Y then it will look for the AD. For example, 1.1.1.0/24 is learned through IBGP and OSPF...t will look at the administrative distance and prefers the lowest value. It will use OSPF since it has an AD of 110, compared to 200 for iBGP.

    The local preference is used when the router has learned multiple paths for a network through BGP, and it has to make a decision which path to use. The default local preference value is 100. Here's an example btw:

    Rene

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