draft-ietf-dnsop-respsize-01.txt

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   3.2. For longer query names, the number of address records supplied will
   be lower.  Furthermore, it is only by using a common parent name (which
   is GTLD-SERVERS.NET in this example) that all 13 addresses are able to
   fit.  The following output from a response simulator demonstrates these
   properties:


      % perl respsize.pl 13 13 0
        common name, average case: msg:303    nsaddr#13 (green)
        common name,   worst case: msg:495    nsaddr# 1 (red)
      uncommon name, average case: msg:457    nsaddr# 3 (orange)
      uncommon name,   worst case: msg:649(*) nsaddr# 0 (red)
      % perl respsize.pl 13 13 2
        common name, average case: msg:303    nsaddr#11 (orange)
        common name,   worst case: msg:495    nsaddr# 1 (red)
      uncommon name, average case: msg:457    nsaddr# 2 (orange)
      uncommon name,   worst case: msg:649(*) nsaddr# 0 (red)


   (Note: The response simulator program is shown in Section 5.)


   Here we use the term "green" if all address records could fit, or
   "orange" if two or more could fit, or "red" if fewer than two could fit.
   It's clear that without a common parent for nameserver names, much space
   would be lost.


   We're assuming an average query name size of 64 since that is the
   typical average maximum size seen in trace data at the time of this
   writing.  If Internationalized Domain Name (IDN) or any other technology
   which results in larger query names be deployed significantly in advance
   of EDNS, then more new measurements and new estimates will have to be
   made.


   4 - Conclusions


   4.1. The current practice of giving all nameserver names a common parent
   (such as GTLD-SERVERS.NET or ROOT-SERVERS.NET) saves space in DNS
   responses and allows for more nameservers to be enumerated than would
   otherwise be possible.  (Note that in this case it is wise to serve the
   common parent domain's zone from the same servers that are named within
   it, in order to limit external dependencies when all your eggs are in a
   single basket.)


   4.2. Thirteen (13) seems to be the effective maximum number of
   nameserver names usable traditional (non-extended) DNS, assuming a
   common parent domain name, and assuming that additional-data truncation
   is undesirable in the average case.




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   4.3. Adding two to five IPv6 nameserver address records (AAAA RRs) to a
   prototypical delegation that currently contains thirteen (13) IPv4
   nameserver addresses (A RRs) for thirteen (13) nameserver names under a
   common parent, would not have a significant negative operational impact
   on the domain name system.


   5 - Source Code


   #!/usr/bin/perl -w


   $asize = 2+2+2+4+2+4;
   $aaaasize = 2+2+2+4+2+16;
   ($nns, $na, $naaaa) = @ARGV;
   test("common", "average", common_name_average($nns),
        $na, $naaaa);
   test("common", "worst", common_name_worst($nns),
        $na, $naaaa);
   test("uncommon", "average", uncommon_name_average($nns),
        $na, $naaaa);
   test("uncommon", "worst", uncommon_name_worst($nns),
        $na, $naaaa);
   exit 0;


   sub test { my ($namekind, $casekind, $msg, $na, $naaaa) = @_;
        my $nglue = numglue($msg, $na, $naaaa);
        printf "%8s name, %7s case: msg:%3d%s nsaddr#%2d (%s)\n",
             $namekind, $casekind,
             $msg, ($msg > 512) ? "(*)" : "   ",
             $nglue, ($nglue == $na + $naaaa) ? "green"
                  : ($nglue >= 2) ? "orange"
                       : "red";
   }


   sub pnum { my ($num, $tot) = @_;
        return sprintf "%3d%s",
   }


   sub numglue { my ($msg, $na, $naaaa) = @_;
        my $space = ($msg > 512) ? 0 : (512 - $msg);
        my $num = 0;


        while ($space && ($na || $naaaa )) {
             if ($na) {
                  if ($space >= $asize) {
                       $space -= $asize;




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                       $num++;
                  }
                  $na--;
             }
             if ($naaaa) {
                  if ($space >= $aaaasize) {
                       $space -= $aaaasize;
                       $num++;
                  }
                  $naaaa--;
             }
        }
        return $num;
   }


   sub msgsize { my ($qname, $nns, $nsns) = @_;
        return  12 +                            # header
                $qname+2+2 +                    # query
                0 +                             # answer
                $nns * (4+2+2+4+2+$nsns);       # authority
   }


   sub average_case { my ($nns, $nsns) = @_;
        return msgsize(64, $nns, $nsns);
   }


   sub worst_case { my ($nns, $nsns) = @_;
        return msgsize(256, $nns, $nsns);
   }


   sub common_name_average { my ($nns) = @_;
        return 15 + average_case($nns, 2);
   }


   sub common_name_worst { my ($nns) = @_;
        return 15 + worst_case($nns, 2);
   }


   sub uncommon_name_average { my ($nns) = @_;
        return average_case($nns, 15);
   }


   sub uncommon_name_worst { my ($nns) = @_;
        return worst_case($nns, 15);
   }




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   Security Considerations


   The recommendations contained in this document have no known security
   implications.


   IANA Considerations


   This document does not call for changes or additions to any IANA
   registry.


   IPR Statement


   Copyright (C) The Internet Society (2003-2004).  This document is
   subject to the rights, licenses and restrictions contained in BCP 78,
   and except as set forth therein, the authors retain all their rights.


   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR
   IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


   Authors' Addresses


   Paul Vixie
      950 Charter Street
      Redwood City, CA 94063
      [phone]
      [e-mail]


   Akira Kato
      University of Tokyo, Information Technology Center
      2-11-16 Yayoi Bunkyo
      Tokyo 113-8658, JAPAN
      [phone]
      [e-mail]










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