13 servers? Was: Re: [ga] Domains with no Name Servers listed

[Karl Auerbach <karl@CaveBear.com>]

On Wed, 16 Apr 2003, Jay Westerdal wrote:

> In the Verisign RRP is it not a requirement to have a minimum of 1 name
> server but no more then 13.

The number 13 comes is derived from a computation of how many name server 
name strings will fit into a DNS UDP packet that fits within the obsolete 
512 byte limitation set by the RFC.

But... that computation is not valid when the list of name servers 
contains servers with long names, particularly when they do not share the 
same suffix (and thus can not be "compressed" using the DNS name 
compression algorithm.)

In other words, if you have servers like:
averyverylonghostnameformydnsserver.verylongbighonkinglongnamestring.verylongbighonkinglongsubdomainstring.someveryveryverylongdomainname.com

then you are not going to be able to squish 13 names into the list without 
exceeding the 512 byte limit.  And I can assure you that you do not want 
your DNS queries to get back the truncated bit and transition to TCP as 
the transport - if you think the net is slow now...

On the other hand if you have short names like
a.cie.com
b.cie.com
c.cie.com

then one can fit a lot more than 13 name servers into the list.

IPv6 and IDN's will change the way the calculations turn out.

		--karl--


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