Re: BGP "Allowas-in" -- scenarios to use this?

From: Rick Mur <rmur_at_ipexpert.com>
Date: Tue, 18 Aug 2009 22:43:09 +0200

And of course a good SP will strip that AS from the AS_PATH using 'as-
override' or some similar feature :-)

-- 
Regards,
Rick Mur
CCIE2 #21946 (R&S / Service Provider)
Juniper JNCIA-ER & JNCIA-EX
MCSA:Messaging, MCSE
Sr. Support Engineer  IPexpert, Inc.
URL: http://www.IPexpert.com
On 18 aug 2009, at 18:42, ALL From_NJ wrote:
> Great example and explanation  Marko.
>
> As Marko says, it is very common w/ MPLS, as some SPs will assign each
> customer only one private AS for all their sites, nd in some cases,
> regardless of the number of sites.
>
>
>
> On Tue, Aug 18, 2009 at 10:49 AM, Marko Milivojevic <markom_at_markom.info 
> >wrote:
>
>> On Tue, Aug 18, 2009 at 14:34, Adrian<ccie2323_at_gmail.com> wrote:
>>> dun think it will ever happen. unless for private AS. B Have 2  
>>> remote
>> sites
>>> that is having the same as that transit a different AS in the  
>>> middle.
>>>
>>> AS100-AS200-AS100
>>
>> This is actually somewhat common in MPLS VPN deployment scenarios.
>> Imagine Enterprise (say with AS65000) that has MPLS provider with AS
>> 65100. They have several sites and run BGP:
>>
>> (site1: AS65000) --- (MPLS: AS65100) --- (site2: AS65000)
>> (site3: AS65000) ----^
>>
>> As you can see, all customer sites are in AS65000. When update from
>> site1 arrives to either site2 or site3, AS_PATH will look like "65001
>> 65000". Site2 will, of course, reject this as looped.
>>
>> One of the solutions how to overcome this situation is to use "bgp
>> allowas-in". There are others, but they require configuration by
>> service provider - who may be unwilling to change their  
>> configurations
>> and let customers deal with their issues, without getting too
>> involved.
>>
>> --
>> Marko
>> CCIE #18427 (SP)
>> My network blog: http://cisco.markom.info/
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
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>
>
> -- 
> Andrew Lee Lissitz
> all.from.nj_at_gmail.com
>
>
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Received on Tue Aug 18 2009 - 22:43:09 ART

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