From: Gregory Gombas (ggombas@gmail.com)
Date: Mon Jul 30 2007 - 18:22:40 ART
Thanks Scott,
Is this what smaller companies typically do?
I guess AS path prepending is out of the question considering your
service providers will remove the private AS anyway?
And finally, with millions of companie out there, I'm shocked that
they haven't run out of AS numbers already. What are all these
companies doing?
On 7/29/07, Scott Morris <smorris@ipexpert.com> wrote:
> Heheheh.. In the event of your multihoming, I think your upstream may be a
> little upset to know that you are impersonating them and only advertising a
> small set of routes (e.g. not wanting to be a transit path!).
>
> So very often we'll have private AS's to use for purposes like this where
> you want to run BGP, but are not multihoming, or simply that you don't have
> provider independent space and even if you are multihoming you aren't really
> advertising anything.
>
> If you DO have something to advertise, then you need an AS number. I
> believe they're only on 49000 something for assignments, so there's still
> room to grow.
>
> At the same time, they're just wrapping up the 4-byte AS number extensions,
> so no fear of running out now!
>
> But with the interconnected world of BGP, if you truly have a need to run
> BGP, then you most likely will need your own AS number to do so. Otherwise,
> work with your ISP for private AS assignment, but don't impersonate them,
> they will likely not find the humor in it!
>
>
> Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE
> #153, CISSP, et al.
> CCSI/JNCI-M/JNCI-J
> VP - Technical Training - IPexpert, Inc.
> IPexpert Sr. Technical Instructor
>
> A Cisco Learning Partner - We Accept Learning Credits!
>
> smorris@ipexpert.com
>
> Telephone: +1.810.326.1444
> Fax: +1.810.454.0130
> http://www.ipexpert.com
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Gregory Gombas
> Sent: Sunday, July 29, 2007 2:05 PM
> To: Group study
> Subject: Unique AS number when connecting to two different ISP's?
>
> When connecting to the internet via two different ISP's, why is it necessary
> to have a unique AS?
>
> What if you simply configured your BGP router with the same AS number as one
> of your ISP's?
>
> Considering there are only 64511 unique AS numbers, I assume that most if
> not all the AS numbers are already taken. What do companies do in the case
> they cannot get their own AS number and need to multihome?
>
> Thanks,
> Greg
>
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