North American Network Operators Group

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Re: How Not to Multihome

  • From: Patrick W. Gilmore
  • Date: Mon Oct 08 18:24:56 2007

On Oct 8, 2007, at 5:55 PM, Justin M. Streiner wrote:
On Mon, 8 Oct 2007, [email protected] wrote:

I have a client that wants us to advertise an IP block assigned by another
ISP. I know that the best practice is to have them request an AS number
from ARIN and peer with us, etc. However, I cannot find any information
that states as law. Does anyone know of a document or RFC that states

It's not 'law' per se, but having the customer originate their own announcements is definitely the Right Way to go.

That is not at all guaranteed.

Some providers take a pretty dim view of seeing chunks of their address space show up in advertisements originating from someone who isn't one of their customers. It can make troubleshooting connectivity problems for that customer (from the provider's point of view) very painful, i.e. "Hey, this AS, who isn't one of our customers, is hijacking IP space assigned to one of our customers!" The provider could then contact your host's upstream (s) and ask them to drop said announcement under the impression they're stopping someone from doing something bad.

If you do you have permission from the owner of the block, you Should Not Announce it.

If the owner gives you permission and can't figure out why their block is originated by another ASN as well, they need help. (Yes, I realize the latter part of the last sentence is probably true for the majority of providers, but whatever.)

In either case, your hypothetical question should not hold.

Also, if some network out there aggregates prefixes in an aggessive/ odd manner, the disjoint announcement, and the reachability info it contains could be washed out of their routing tables, causing connectivity problems.

How is this different than if the customers gets their own ASN and announces a sub-block from one of the providers?

Or are you suggesting they should get PI space?