Re: How Not to Multihome

["Patrick W. Gilmore" <patrick () ianai net>]

On Oct 8, 2007, at 5:55 PM, Justin M. Streiner wrote:
> On Mon, 8 Oct 2007, Keegan.Holley () sungard com 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
> > this?
>
> 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?

--
TTFN,
patrick