From: Ryan (ryan95842@gmail.com)
Date: Mon Jul 30 2007 - 19:24:09 ART
Most companies do not get multi-homed with two ISP's. There is generally not
a need for this and most ISP's have strict address assignment requirements
that most business's cannot meet. To peer BGP with two ISP's requires a /24
address block minimum (ISP's will not announce any longer prefix than a /24)
and companies have a real hard time justifying the usage requirements that
warrant a /24. Most can only justify a /29 at best which is a typical
default assignment.
Now, major companies that have a large Internet presence can usually justify
the address space and can get a second connection with another ISP and their
own AS number (there are fee's for an AS number, they are not free).
So if your a small business that can not justify the expense of an AS and
the address space usage to multi-home with two ISP's, your only options are
to multi-home with the same provide and use a Private AS.
-Ryan
On 7/30/07, Gregory Gombas <ggombas@gmail.com> wrote:
>
> 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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