I will preface this by saying I am not a regular FreeBSD user, and
although I've had a few successful installations in the past, I'm not
very current on the material.

I recently got the itch to try a new FreeBSD install, and not having a
real purpose for the build, I went for some bleeding edge and grabbed
7.0-BETA3-i386-bootonly.iso.  I went through the standard graphical
install, partitioned disks, selected the package set, and all seemed
well.  When I came to the network portion, I selected no IPv6 and yes
DHCP.  DHCP came up correctly from my LAN DHCP server, and I moved on.
 I picked a mirror that didn't yet have beta3 on it (apparently) and
the download failed.  I went to try again, but the next mirror I tried
wouldn't connect.  Pretty soon, the installer was insisting that it
can't find any domains via dns, and that I should check the network
config.  Well sure enough the network settings are right (not
surprising considering they'd *just* worked, and I hadn't changed
them), my dns server is fine, but the installer won't so much as find
ftp.freebsd.org.

I figure hey, that's what you get for trying beta software, let's try
something a little less radical and maybe it will work.  I opt for the
6.3 RC1 bootonly iso next.  Wouldn't you know it, same results.  If
you don't pick a functional mirror on the first try, suddenly the
installer forgets how to look up hosts in dns.  After rebooting the
installer a few times, I manage to confirm that if I get the right
combo on the first time through the installer (ftp passive,
ftp1.us.freebsd.org worked in this case), things work perfectly.  If I
do something silly like trying http without a proxy, or picking a
mirror that doesn't have the distro or doesn't connect, after one or
two cycles dns lookups magically fail and I have to reboot.  Ironically,
even domain names that work the first time through will start to fail
to resolve after one or two passes.  Sure enough, I went back to my
7B3 disc, and using my winning combo of ftp/passive, ftp1.us, the
install works right off the bat.  (Note that these combinations are
just examples of what works for me, right now.

I'm not suggesting that the connection type or the mirror name is
somehow responsible for things being broken; it's merely for completeness
of story.)

So, the essence of this bug report is this:  If I fail to begin the
installation download on the first couple tries, the installer
habitually becomes unable to resolve dns until a reboot is performed.
This affects at least 6.3 and 7.0, but could go back much further.

How-To-Repeat: Run netboot installer, purposefully connect to unavailable or
misconfigured mirrors a few times, then watch as further attempts fail
to resolve dns.