svn commit: r238622 - head/etc/rc.d

[Hiroki Sato]

Hiroki Sato <hrs at FreeBSD.org> wrote
  in <20120803.124305.1981901625663633450.hrs at allbsd.org>:

hr> Maksim Yevmenkin <emax at freebsd.org> wrote
hr>   in <CAFPOs6pM8qrR72kOtZzO90wYembNrtzw7=ig-NSfudJZA7bp6Q at mail.gmail.com>:
hr>
hr> em> of course :) we have ipv4 systems in production that make use of
hr> em> getaddrinfo(3) api. when a particular dns name is resolved, and,
hr> em> multiple A records are returned, the results get sorted according to
hr> em> the "default" address selection policy. rfc3484 has a set of rules
hr> em> according to which results should be sorted. all of the rules do not
hr> em> apply in our case, except one - the rule #9. the idea is that ipv4
hr> em> addresses are "converted" to ipv6 addresses and then longest prefix
hr> em> match sorting is applied. in other words, if your system ip address
hr> em> happens to share high bits with the ip address from the A record, the
hr> em> IP address from the A record will always be preferred. of course,
hr> em> longest prefix match is performed  without any extra information such
hr> em> as netmask and/or cidr. it really is just matching high bits of the
hr> em> address.
hr> em>
hr> em> so, what we found out, is that some systems tend to favor a particular
hr> em> ip address (from a bunch of ip addresses returned by name resolution)
hr> em> because 4 high bits were the same. basically, round-robin dns was
hr> em> completely shot.
hr>
hr>  Is that issue solved by applying the attached patch and setting
hr>  net.inet6.ip6.longestmatch_mapped=0?
hr>
hr>  I do not think it is a good idea to use the empty rule to solve it
hr>  because if the system has to support IPv6 as well the empty rule has
hr>  negative effect.  Adding flag to the IPv4 address line in the policy
hr>  or adding a sysctl sounds a reasonable solution to me.

 Gr, I got a wrong idea about the issue.  What you want is to disable
 longest match in the dest addr selection.  It needs a change in
 comp_dst() in getaddrinfo.c.

-- Hiroki
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