[arin-ppml] Rationale for /22

Jon Lewis jlewis at lewis.org
Mon Aug 3 13:55:43 EDT 2009

On Mon, 3 Aug 2009, Kevin Kargel wrote:

>> In the 2009 backbone, you either carry "full" routes down to /24 or
>> you carry partial routes and a default. The default takes you to
>> someone who does carry full routes. Whether those partials are
>> composed by filtering on the RIR minimums or using some other criteria
>> (e.g. distant routes) makes little difference.
>> IMHO, that's the reality on the ground that ARIN policy should target,
>> not a hypothetical network in which folks carry partial routes without
>> a default and it works out for them.
> As a piece of trivia, I know of one small multihomed ISP who runs BGP to
> announce routes, carries no routes at all except for direct connected peers
> and has two default routes with some rather complex priorities and mapping
> to upstreams that do carry full routes and it seems to work quite well for
> them.

That's really not at all relevant and can be considered a subset of 
filtered routes + default.

AFAIK, it's not an uncommon setup.  I have multiple customers doing it as 
they wanted to multihome to protected against single circuit or single 
provider failures, but didn't want the expense of one or more routers big 
enough to deal with full routes.  These customers effectively have a 
primary and a backup internet provider.

  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
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