ISP Policies

Thu Sep 9 05:17:07 UTC 2004

Tulip Rasputin wrote:

> So can you give me an example of why and when would an ISP *not* want 
> its traffic to flow via some other AS(es). Is it a normal policy to 
> have, and do most of the ISPs have such policies in place? 

If you don't have a transit agreement and aren't sitting in the top tier 
peering list, you will not want traffic to flow via some other AS(es) as 
they may be blocking your advertisements inbound.  This is really a 
"tier" question.  Most end-node ASNs you will find do not want to 
provide transit traffic between their upstream ISPs (asking for trouble 
and bandwidth saturation) or at least make it a short-term emergency act 
of altruism.

You may have "dedicated" circuits or bandwidth or CIRs for certain 
services from YOUR ASN only.  They may not accept traffic that doesn't 
originate in your ASN and you're wasting time to try.  Part marketing, 
part business, part political as what transit you will support (and what 
transit your upstream(s) support).

In more practical terms, we have dedicated circuits for H.323 video, an 
IPSec link to our parent campus with the university-wide SAP/R3 traffic, 
another link restricted to ESNet (immediate peers only).  For a 
commercial ISP your mileage may vary as you are, above a certain level, 
providing transit between different administrative domains (or ASNs, or 
whatever).  You can do this with statics, with policy routing (or null 
routing), or in a local OSPF or whatever routing mechanism you have at 
your border.

Jeff