Re: major DNS hiccup

Michel Talon wrote:
Mike Scott <usenet.10@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
This one seems to fall heavily into the "can't happen" category, and I'm stuck for ideas: would /very/ much appreciate pointers about where to look.

Thanks in advance.


Could it be that you have somewhat firewalled TCP and leaved only UDP?
Some DNS queries are done via UDP, others via TCP, so firewalling TCP is
not a good idea.


I'm 99.9999% sure it's not firewall-related. If it were, I would think either all or no traffic would pass at all; and I've tried a different machine (with a very liberal firewall config). I see traffic passing both ways (all udp, no tcp, incidentally), and all with correct checksums (another contributor to this thread suggested checking this), and nothing being blocked. Oh, and I've just tried removing pf's 'scrub' rule - an act of desperation that made no difference at all :-(

What I get is nameserver reply packets from assorted unrelated servers (even the root servers) with defects in them - either no answer record but with the question returned to me (as seems normal), or no answer /and/ no question (the latter being flagged in the reply as 'format error').

It seems that this is occurring even when the lookup is (at application level) successful - and that duplicate replies from different servers often provide the missing information.

I've now dropped back to using my ISP's name servers plus hosts files for the LAN addresses, which works but is not really satisfactory and only plasters over the problem - which started suddenly last thursday if I recall.

Maybe I've just not fed the Gremlins enough last week?

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