[CentOS] dhcpd options

Thu Mar 21 17:39:48 UTC 2013
m.roth at 5-cent.us <m.roth at 5-cent.us>

A few weeks ago, suddenly, reading news at lunch, I could not get to
nytimes.com. I could ping it, and nslookup it, and if I put the IP address
in place of the name, it was fine.

After *much* back and forth over a ticket I put in, over the last week or
so, our group figured it out: It *seemed* to be related to IPv6, and
there's only *some* few sites, such as the Times, and Orbits, and one or
two others I found, while, say, the Washington Post, or Huffpo, etc, were
fine; and I could make it work by putting IPV6INIT="no" in ifcfg-eth0 and
restarting the network, but another admin got it nailed, we *think*:
apparently the M$-based DNS resolver's sending back extended DNS packets,
and we gag. tcpdump saw us asking for an A record, then an AAAA record,
then using search....

But putting the *very* counterintuitive option edns0 in /etc/resolv.conf,
it works instantly, no caching, no nuthin'. Taking that out breaks it

My question: it *appears* that we could add
option edns0
to dhcpd.conf on the server, and it would fix it for everyone on our subnet.

Have I misunderstood what I'm reading in the manpages?