[115084] in North American Network Operators' Group
Re: Multi site BGP Routing design
daemon@ATHENA.MIT.EDU (Steve Bertrand)
Fri Jun 5 22:00:17 2009
Date: Fri, 05 Jun 2009 21:59:54 -0400
From: Steve Bertrand <steve@ibctech.ca>
To: "Michael K. Smith" <mksmith@adhost.com>
In-Reply-To: <C64F164E.785BD%mksmith@adhost.com>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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Michael K. Smith wrote:
> On 6/5/09 4:42 PM, "Steve Bertrand" <steve@ibctech.ca> wrote:
>
>> Justin Krejci wrote:
>>
>>> If the private link between the two sites fails, will BGP allow for us to
>>> access the IP subnets at site 2 from site 1 via the internet given that both
>>> sites are advertising under the same ASN?
>> No, because your router at site 2 will not accept any prefix with its
>> own AS in the AS_PATH (which site 1 would be advertising from).
>>
>>
> If you're running Cisco with the right IOS it looks like you could use the
> 'neighbor x.x.x.x allowas-in' command to accept your own AS. Then you would
> just have to set your local route origination so that the appropriate routes
> were withdrawn when the backnet link goes down.
I stand corrected.
I've read about this, but does anyone have operational experience with
it that they can share?
Even though we are a very small SP, I always feel that going against the
traditional grain when doing things like this may leave a trail of
undocumented, hard-to-troubleshoot issues in the future.
To rephrase the OP's question, would it be BCP to acquire a second ASN,
and without further de-aggregating, continue advertising each site's IP
space to the DFZ, but from dissimilar ASs as opposed to the same one?
Steve
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