[c-nsp] Multihoming Question

[Justin M. Streiner]

On Wed, 13 Dec 2006, Paul Stewart wrote:

> Hi there...  I posted this yesterday by accident on the NSP list, sorry
> to those of you who are subscribed to both....
>
> We have some customers who are seeking connections from us (ISP) and
> another ISP for redudancy.  This will be offered as a managed package
> deal to the customer.
>
> Because this will involve BGP from both ISP's, the end customer would
> require an AS number and their own IP space.  The problem comes into
> place with the customer's size and the fact that they will most likely
> not require even a full /24 block in most situations and really their
> own AS number is probably a wasted resource.

If a customer needs to advertise reachability to the rest of the Internet 
and they don't strictly follow the routing policy of only one upstream, 
i.e. they are connected to more than one upstream provider, then they need 
to advertise public, registered IP space, originating from a public, 
registered AS.

If a customer is multihoming to >1 upstream, that's generally enough 
justification for them to get a /24 from one or more of their upstreams.

The reason for a /24 is that many networks filter out BGP advertisements 
for anything longer (smaller) than that, so giving a customer anything 
smaller than that to announce into the global Internet routing table is 
likely to cause lots of headaches in terms of troubleshooting 
reachability problems down the road.

You could do BGP w/private or semi-private AS only if all of the 
customer's upstream connections went to only one provider.  As soon as you 
bring a second upstream into the mix, you need a public AS.

jms