From: Packet Man (ccie2b@hotmail.com)
Date: Fri Feb 27 2004 - 16:19:48 GMT-3
Hey Matt,
As it so happens, I've just recently reviewed the use of the
nei...next-hop-self command. It can be confusing because it's effect is
different depending on whether you're dealing with routes being advertised
to an external bgp peer or internal bgp peers.
Advertising routes to an ebgp peer over:
P2P serial link
next-hop-self not needed b/c bgp's default behavior is to set next-hop to
itself
Ethernet (or T/R)
next-hop-self isn't needed but can be used b/c ebgp peer can reach the
next-hop set by the ibgp peer without having to make a pit stop at the ebgp
peer
Multipoint Frame Relay or ATM interface
next-hop-self REQUIRED b/c ebgp peer can't reach the next hop without going
through the hub router and would therefore drop pkts to that ip address.
Advertising routes to an ibgp peer:
Next-hop needed if ibgp peer doesn't have subnet of link between the 2 AS's
in it's route table.
It took me a while to absorb these concepts and it's critical to understand
these things if you're going to do well on the BGP portion of the lab, so I
suggest if you don't fully understand what I'm saying ( which I know is
difficult without using diagrams) you study very thoroughly Halabi's
explanation on this topic. And, keep in mind, that the reasons to use this
command are different depending on whether your router is advertising routes
to a ebgp peer or a ibgp peer.
HTH
>From: "Matt Mullen" <MMullen@nettechgroup.com>
>Reply-To: "Matt Mullen" <MMullen@nettechgroup.com>
>To: <ccielab@groupstudy.com>
>Subject: BGP Route Reflector Question
>Date: Fri, 27 Feb 2004 13:29:26 -0500
>
>Is it best practice to configure next-hop-self on route reflector
>clients? The reason I ask is that the solution to one of the labs i'm
>working on shows this, even though it is possible to ping all BGP
>advertised networks without having next-hop-self configured.
>
>Thanks,
>Matt
>
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