At 11:42 -0500 11/29/06, Emin Gun Sirer wrote:
Let's not torque the discussion off topic. Free market economics does
not come to bear on the issue because there is no free market to speak
of for registries.
What did I say about frictionless surfaces?
A quick question: Right now, we'd like to have a domain delegated to a
large number (say 100+) of nameservers. The registrars we have gone
The terminology used here indicates a need for a deeper understanding of DNS.
through impose a limit on the number of nameservers they are willing to
accept. Is this a limit stemming from the .COM registry, or is there a
registrar out there that will let us delegate a .COM domain to a few
hundred nameservers? (And no, not all nameservers need to be returned in
response to every query. A random sampling would be fine).
The conventional limit on the number of name servers for a zone is
derived from the pre-EDNS0 limit of 512 bytes in a UDP'd DNS message.
When you query for the root zone SOA you get back the SOA, 13 NS
records, and 13 glue A records. If it were 14, then the message
would be truncated and probably lead to a TCP connection attempt.
From this hard (operations) limit, the notion of 13 as maximum crept
into registry software. And not just .COM.
Ideally, the limit would be lower, as IPv6 wasn't invented when the
number 13 was derived. To stay under the 512 limit and still include
AAAA records, a lower limit would be needed.
Your parenthetical comment is contrary to one of the most important
principles in the DNS, coherency. Especially high up in the
hierarchy. It would be hard to debug problems if the returned set of
servers in a referral changed very rapidly. There is the practice of
tailoring answers to a querier, although this is globally incoherent
in the strict sense at least the answers to the querier in question
stay fairly constant (and coherent from different available sources).
Of course, the 13 name limit does not limit you to 13 name servers.
With anycast, the number can be unbounded subject to the concerns
with routing. And if you add in load balancers you can have even
more servers. It depends on how you count 'em.
--
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Edward Lewis +1-571-434-5468
NeuStar
Dessert - aka Service Pack 1 for lunch.
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