From: Peter van Oene (pvo@xxxxxxxxxxxx)
Date: Tue Mar 12 2002 - 19:35:00 GMT-3
Sorry about my previous message sent on 1 hour sleep :) My grammar is
usually somewhat better. Anyway, I think you have it, but let me build it
out a little more for clarity.
Route Reflection:
Simply used to offset the scaling limitations of the IBGP full mesh. It
specifically relaxes the rule that states that IBGP learned routes cannot
be passed along to another IBGP router. In other words, all IBGP
information must be first hand, ie directly communicated from
source. Attributes, including Next_Hop, are not modified in any way during
this process which results in a route reflector client not actually needing
to be aware that it is one.
Next-Hop Self:
Simply a tool that allows one to manipulate the BGP Next_Hop address
associated to some NLRI. This generally allows one to minimize the size of
an IGP topology by not including ASBR external links toward BGP external
peers. In these cases, the ASBR simply replaces the Next_Hop attribute
with its own address which should already be in the IGP thereby allowing
all other routers in the AS to satisfy their BGP Next_Hop resolution
requirements for the prefixes which that ASBR brings into the AS. Of note,
in slight contrast to your post, this is set by the transmitting router,
not the receiving router. Indeed, changing next hop as in inbound policy
(not possible in cisco) will cause some nasty issues.
pete
At 01:04 PM 3/12/2002 -0600, Michael Snyder wrote:
>I agree. Thanks for everyone that answered my question. I believe my
>confusion came from working with a two router pod where split horizon
>wasn't an issue.
>
>
>Yes, this to have to functional differences. A router reflector
>overcomes the IBGP split horizon rule:
>
> If I learn it via IBGP I will not pass it to my IBGP neighbors.
>
> Next-hop-self:
>
> Overcomes the next hop propogation problem. If the next hop being
>advertised for a given route
>is not reachable, I can't use that route, so I set the Next hop to be
>the router who advertised it to me,
>instead of the next hop EBGP router that my internal router might not
>have knowledge of.
>
>Michael Snyder wrote:
>
>
>I've been reading up on BGP lately, and have come up with a question.
>
>
>
>
>
>Is there a functional difference between setting a neighbor as a route
>
>
>reflector client, or setting a neighbor as next hop self? Assuming 'no
>
>
>sync', to my mind these commands seem to do the same thing. The same
>
>
>network topology and limits seem to apply to each command.
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