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Re: Multihoming an end user

At 09:15 PM 9/23/05 -0500, Eric Cunnningham wrote:
>My understanding was that if the addresses weren't specifically 
>allocated to us straight from ARIN, we couldn't truly multihome.  

I don't think it matters who actually gave u the address block.  Once u have
an autonomous system number that block should be independently routable from
anywhere on the internet.  Both of ur ISP's will have to agree to accept ur
routes.  Then it's ur responsibility to get ur router to propagate ur routes
out to them.

>Otherwise our second ISP would try to route to our first ISP's addresses 
>through that first ISP rather then direct through their link to us.  If 
>we apply for an ASN, can we associate our first ISP's /29 (or /24 if 
>need be) to our ASN?  Does our primary ISP need to release it to us or 
>be multihomed themselves?

It depends.  U can get ur own brand new /24 block or take over ISP #1's /24
block.  ISP1's router will then have 2 routes to u.  First direct, second
back out through the internet to ISP2.  The same goes for ISP2.  This is
rather inefficient since traffic has to backtrack a lot if one link goes
down.  It all depends on how far out ur route can be propagated.  Getting it
all the way to both ISP's border routers is a good minimum.  Getting it to
both of ur ISP's peer's core routers is best.  That way traffic can be
routed appropriately much closer to the source.  Path determination closer
to the source equals better efficiency.  U can weight the routes to prefer
one or the other but I would make them equal.  There's no reason to leave
one link idle. I'm not an expert on eigrp so I can't give too much more
detail.  Multihoming is about the only way to have transparent redundancy.

"...ne cede malis"


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