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Thread Index [isp-bgp] bgp inconsistent-as
On 3/18/06, Mostafa Ali <mmostafa@...> wrote:
> Hi Everybody
>
> Referring to the Multihomming best practice which was really a good
> thread , I see most of you takes the inconsistent as path as a serious disadvantage when using private AS in multi-homed systems
>
> AFAIK , Inconsistent as in not bad nor illegal but im interested to know all the possible drawbacks that could result from your
> point of view
Mostafa,
I'd disagree with you about it being "bad". Although, I agree
it would technically "work", but any self-respecting network
engineering type would ensure they do not participate in any
inconsistent routing. Before people jump up and start to flame me,
I will explain.
In the world of BGP, we base a lot of the routing decisions
based on the origin AS, or autonomous system. When a network
multi-homes, they become an autonomous system, hence the term.
Anyway, for those thinking "it technically works, why not do it".
Well, for one, it makes the end network look "fishy". Most of the
time when you see an inconsistent-as, it's the result of a
configuration error, not something that was intended to occur.
An AS's information would, or has been used on a regular basis to
track abuse, assistance with troubleshooting. I've also seen folks
use inconsistent-as information to determine IP space hi-jacking,
since those networks would typically inject routes from a router they
have access to, do their nasty stuff and then retract the routes.
All being considered "inconsistent".
Anyway, I've gone on enough about this. But long story short.
If you're able to be autonomous, be autonomous. It will save you a
LOT of time, frustration and heacahes when your network desides to buy
new transit connectivity, peer or just expand, as most networks hope
to do.
charles
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