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

  • From: Randy Bush
  • Date: Mon Mar 28 10:05:01 2005

>> a tier-1 network does not get transit prefixes from any other
>> network and peers with, among others, other tier-1 networks.
>> a tier-2 gets transit of some form from another network, usually but
>> not necessarily a tier-1, and may peer with other networks.
>> this does not please everyone, especially folk who buy transit and
>> don't like discussing it.  and there are kinky corners
> Even this is debatable (& I know you know this Randy).

in this forum, everything is debatable.  some portion of the debate
makes sense.  ymmv.

> Firstly, peering isn't binary. Is peering vs transit a distinction based on
> routes taken / accepted & readvertised, or on cost? Does "paid for peering"
> count as peering or transit? If you pay by volume? If you pay for "more
> than your fair share" of the interconnect pipes? (if the latter, I am
> guessing there are actually no Tier 1s as everyone reckons they pay for
> more than their fair share...).

pay?  did i say pay?  i discussed announcement and receipt of
prefixes.  this was not an accident.  it is measurable.

> Secondly, it doesn't cover scenarios that have have happened in the past.
> For instance, the route swap. EG Imagine networks X1, X2, X3, X4 are "Tier
> 1" as Randy describes them. Network Y peers with all the above except X1.
> Network Z peers with all the above except X2. Y & Z peer. To avoid Y or Z
> needing to take transit, Y sends Z X2's routes (and sends Z's routes to X2
> routes marked "no export" to X2's peers), and Z sends Y X1's routes (and
> sends Y's routes to X1 marked "no export" to X1's peers). Perhaps they do
> this for free. Perhaps they charge eachother for it and settle up at the
> end of each month. Perhaps it's one company that's just bought
> another.

seems to me that, if you look at the prefixes, it's pretty clear.


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