From: Ayman Hamza (ayhamza@cisco.com)
Date: Sun Sep 29 2002 - 20:07:11 GMT-3
Justin;
PLS see inline ;
Regards
-Ayman
> From nobody@groupstudy.com Mon Sep 30 00:23:54 2002
> From: Justin Cook <Justin.Cook@computerland.co.nz>
> To: "'ccielab@groupstudy.com'" <ccielab@groupstudy.com>
> Subject: Query about BGP
> Date: Mon, 30 Sep 2002 10:05:19 +1200
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> Reply-To: Justin Cook <Justin.Cook@computerland.co.nz>
>
> The following is the scenario
>
> You and another company connect via BGP through a Provider (diff or same
> does not matter) you also have a backup link between your AS's (you and
> customer)
>
> AS100--------------------------AS200
> + +
> + +
> AS1(Customer)-------------AS2(You)
>
> I noticed when reading Cisco Press Internet Routing Architectures that they
> seem to use the following two commands alot
>
> 1. Neighbor CUSTOMER next-hop-self
>
> And
>
> 2. Neighbor ISPAS200 filter-list 10 out
>
> Ip as-path access-list 10 permit ^$
>
> I know that 1. is used so that the customer router knows that the next hop
> is your router for routes learned from the ISP as you do not use an IGP
> between yourself and the ISP
Not only for the routes learned from the ISP, but for all the routes
advertised to this CUSTOMER EBGP enighbor includoing your inner AS routes !
>
> And that 2. is used to stop the backup link between you and you customer
> being used as a bridge
correct, this is to prevent your AS to be transit AS for the CUSTOMER AS
, so you are enjecting only routes that are ""originally"" originating
from your AS.
>
> But is there any other reason the impression I got from the book is this is
> a standard configuration and used widely is this the case.
What I can confirm is that point # 2 is widely used for end customers AS's
when connected to dual ISPs, so you want to advertise to each ISP only your
originally local routes injected from your AS , which means preventing your
AS from ""leaking"" routes frfom other AS(s) as I said when you are dually
connected to external AS - or more than two external AS - .
Point # 1 depends on the situation actually!! Which means you have to ask your
self this question:
""Does my BGP neighbor know the IP ADDRESS in the NEXT-HOP attribute in the
BGP updates I have sent to it ?? " If yes, no need to use this command. if
no use it.
Hope that helps.
Ayman
>
> Also please comment if my statements above do not ring true
>
>
> Thanks
>
> --
> Justin Cook
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