From: Shahid Ansari (shahid1357@gmail.com)
Date: Wed Oct 29 2008 - 05:21:35 ARST
If you will not do next-hop self it will not consider "Best" by BGP.
You have two choices
1)Advertise ebgp neighbor`s IP in IGP
2)Use next-hop self that point to IBGP peer .
On Wed, Oct 29, 2008 at 8:16 AM, Reza Toghraee <reza@toghraee.com> wrote:
> Nit,
>
> Since you have IGP reach ability to R1's interface connected to BB1 and
> R3's
> interface connected to the BB2,, you will have reachability to prefixes
> learned from AS254.
>
> BUT, Imagine that you are asked to load-balance traffic on R2 between links
> to R1 and R3.
> In this case since the learened prefixes from R1,R3 share common attributes
> (Weight, LocalPreference, AS-path, Origin, MED), BGP will select the route
> with better IGP metric. Imagine R2 is learning R1's interface connected to
> BB1 as OSPF external BUT learning R3's connection to BB3 as Inter-Area. So
> R2 always prefer link to R3 to reach AS254.
> In this case if R2, has an intra-area connection to R1,R3 you can solve it
> by using next-hop-self command on R1,R3.
> So, R2 will see both IGP metric types are intra-area and you can fix the
> metrics to be equal. Then if you enable the bgp load-balancing for internal
> neighbors, BGP will install 2 routes for each prefix learned from AS254.
> I saw this along a Checkit LAB.
>
>
>
> Reza
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Nitro Drops
> Sent: Wednesday, October 29, 2008 8:54 AM
> To: ccielab@groupstudy.com
> Subject: BGP - Next-Hop-Self
>
> Setup as follows
>
>
> BB1 (AS254) >> EBGP >> R1 (AS100), R2 (AS100), R3 (AS100) >> EBGP >> BB2
> (AS54)
>
> AS100 = Full mesh among R1, R2, R3
>
> There is full IGP reachbility from AS100 to AS254 and AS54.
>
> Qns.) Is there still a need to use 'next-hop-self' on both R1 and R3 to
> neighbor R2. So that R2 will learn R1 as the next hop address to reach
> AS254,
> and R3 as the next hop address to reach AS54 prefixes?
>
> My understanding of using 'next-hop-self' is when there is no IGP routes
> from
> R2 to BB1 and BB2.
>
> Did an ASET lab, solutions showed using 'next-hop-self' even R2 has IGP
> routes to BB1 and BB2.
>
>
> Cheers
> Nit
>
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-- Regards,Shahid Ansari Saudi Arabia(Riyadh)
Blogs and organic groups at http://www.ccie.net
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