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Re: T1 vs. T2 [WAS: Apology: [Tier-2 reachability and multihoming]]

  • From: David Barak
  • Date: Tue Mar 29 14:57:39 2005
  • Comment: DomainKeys? See http://antispam.yahoo.com/domainkeys
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--- John Dupuy <[email protected]> wrote:

> But by the technical description of a "transit free
> zone", then 701 is not 
> tier one, since I have encountered scenarios where
> many AS are transversed 
> between 701 and other networks, not just a peer of a
> peer. Unless, by 
> "transit free zone" you mean "transit trading" where
> large providers permit 
> each other to transit for free. (Which gets back to
> my 'who hurts more' 
> discussion.)
> 

<oversimplification>

Transit = being someone's customer

Peering = permitting your customers to go to your
peer's customers or the peer's network, but not the
peer's peers, without exchange of money.

Any other relationship != peering for my purposes
(although lots of subtly different relationships
exist, the largest networks tend to take a view which
is not too dissimilar to the one shown above)

</oversimplification>

Are you implying that 701 is paying someone to carry
their prefixes?  While I'm not the peering coordinator
for 701, I would find that improbable.  I would expect
that money would flow the other direction (and thus
701 would become a more valuable peer for other
networks).

> I'm willing to be wrong. If any of the large
> providers on the list will say 
> that their network does not transit beyond the
> customer of a peer; and they 
> still maintain full connectivity, I will gladly be
> corrected.

oodles and oodles of people can say this (and already
have).  A paying customer of mine can readvertise
(with a non-munged AS_PATH) any of my prefixes which
they want, and thus provide transit for other people
to reach me.  That does not change the fact that I'm
not paying for transit.

So in short, I would say that T1 vs T2 etc is a
"follow the money":

T1 => doesn't pay anyone else to carry their prefixes,
and runs a default-free network.

T2 => pays one or more T1 providers to carry their
prefixes, may or may not run a default-free network.

T3 => leaf node, pays one or more T1/T2 providers to
carry their traffic, probably uses default route.

YMMV, blah blah blah


David Barak
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