draft-ietf-dnsop-respsize-02.txt

bind 源码 最新实现 linux/unix/windows平台

      ns-ext.isc.org requires 16 bytes
      ns.psg.com requires 12 bytes
      ns.ripe.net requires 13 bytes
      ns.eu.int requires 11 bytes
      # of NS: 4
      For maximum size query (255 byte):
              if only A is considered:     # of A is 4 (green)
              if A and AAAA are condered:  # of A+AAAA is 3 (yellow)
              if prefer_glue A is assumed: # of A is 4, # of AAAA is 2 (yellow)
      For average size query (64 byte):
              if only A is considered:     # of A is 4 (green)
              if A and AAAA are condered:  # of A+AAAA is 4 (green)
              if prefer_glue A is assumed: # of A is 4, # of AAAA is 4 (green)

   (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.  For these examples we use an average/common name size of
   15 octets, befitting our assumption of GTLD-SERVERS.NET as our common
   parent name.




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   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 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 given that response truncation is
   undesirable as an average case, and assuming mostly IPv4-only
   reachability (only A RRs exist, not AAAA RRs).

   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
   #
   # SYNOPSIS
   #    repsize.pl [ -z zone ] fqdn_ns1 fqdn_ns2 ...
   #        if all queries are assumed to have zone suffux, such as "jp" in
   #     JP TLD servers, specify it in -z option
   #
   use strict;
   use Getopt::Std;
   my ($sz_msg) = (512);
   my ($sz_header, $sz_ptr, $sz_rr_a, $sz_rr_aaaa) = (12, 2, 16, 28);
   my ($sz_type, $sz_class, $sz_ttl, $sz_rdlen) = (2, 2, 4, 2);
   my (%namedb, $name, $nssect, %opts, $optz);
   my $n_ns = 0;




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   getopt('z', opts);
   if (defined($opts{'z'})) {
        server_name_len($opts{'z'}); # just register it
   }

   foreach $name (@ARGV) {
        my $len;
        $n_ns++;
        $len = server_name_len($name);
           print "$name requires $len bytes\n";
        $nssect += $sz_ptr + $sz_type + $sz_class + $sz_ttl + $sz_rdlen + $len;
   }
   print "# of NS: $n_ns\n";
   arsect(255, $nssect, $n_ns, "maximum");
   arsect(64, $nssect, $n_ns, "average");

   sub server_name_len {
       my ($name) = @_;
       my (@labels, $len, $n, $suffix);

       $name =~ tr/A-Z/a-z/;
       @labels = split(/./, $name);
       $len = length(join('.', @labels)) + 2;
       for ($n = 0; $#labels >= 0; $n++, shift @labels) {
           $suffix = join('.', @labels);
           return length($name) - length($suffix) + $sz_ptr
               if (defined($namedb{$suffix}));
           $namedb{$suffix} = 1;
       }
       return $len;
   }

   sub arsect {
       my ($sz_query, $nssect, $n_ns, $cond) = @_;
       my ($space, $n_a, $n_a_aaaa, $n_p_aaaa, $ansect);
       $ansect = $sz_query + 1 + $sz_type + $sz_class;
       $space = $sz_msg - $sz_header - $ansect - $nssect;
       $n_a = atmost(int($space / $sz_rr_a), $n_ns);
       $n_a_aaaa = atmost(int($space / ($sz_rr_a + $sz_rr_aaaa)), $n_ns);
       $n_p_aaaa = atmost(int(($space - $sz_rr_a * $n_ns) / $sz_rr_aaaa), $n_ns);
       printf "For %s size query (%d byte):\n", $cond, $sz_query;
       printf "if only A is considered:     ";
       printf "# of A is %d (%s)\n", $n_a, &judge($n_a, $n_ns);
       printf "if A and AAAA are condered:  ";
       printf "# of A+AAAA is %d (%s)\n", $n_a_aaaa, &judge($n_a_aaaa, $n_ns);



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       printf "if prefer_glue A is assumed: ";
       printf "# of A is %d, # of AAAA is %d (%s)\n",
           $n_a, $n_p_aaaa, &judge($n_p_aaaa, $n_ns);
   }

   sub judge {
       my ($n, $n_ns) = @_;
       return "green" if ($n >= $n_ns);
       return "yellow" if ($n >= 2);
       return "orange" if ($n == 1);
       return "red";
   }

   sub atmost {
       my ($a, $b) = @_;
       return 0 if ($a < 0);
       return $b if ($a > $b);
       return $a;
   }

   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 (2005).  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.





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   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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