In a message written on Tue, Dec 09, 2003 at 03:13:12PM +0100, Niels Bakker wrote:
One cannot have discontiguous networks in the same ASN. It's pretty simple: two routing policies, two ASes, two ASNs. Unfortunately you weren't able to convince your customer of this.
This is simply not true, and trying to push it as an absolute elimintes a very good way of configuring customers and conserving resources. Most (all) large ISP's have a "customer ASN". This allows a customer to connect in multiple places, run BGP, and get something approximating real redundancy to that carrier. However, rather than allocate one ASN to each customer, all customers use the same "customer ASN". Yes, that means they must default to the provider (and/or have the provider provide a default route) to reach the other customers using this technique. I believe there are a number of providers with hundreds, or perhaps even thousands of customers using this feature, saving lots of ASN's and causing no problems. Externally this looks fairly neat, there is a single ASN behind the backbone AS with all the customers in it. To make this work you do need to enforce some restrictions. First, the customer ASN must never be connected to another network (this is for multiple connections to a single provider only) to prevent the wonky AS path issues, and second the customer must have a default via some mechanism. -- Leo Bicknell - bicknell@ufp.org - CCIE 3440 PGP keys at http://www.ufp.org/~bicknell/ Read TMBG List - tmbg-list-request@tmbg.org, www.tmbg.org