copying the question section
paul at vix.com
Sat Aug 3 05:47:03 UTC 2002
bind has always copied the question section into the response. some versions
(notably the ill-fated 4.9.2) demanded to see this, but earlier and current
versions only demand that the question section in the response match the one
from the query if it's present at all -- an empty question section in a
response is not treated as an error. some non-bind servers have been sending
back empty question sections for years now and it's been seen to cause no
for the root name servers, copying the question into the response limits the
total amount of space in the 512-octet (pre-EDNS) payload for the answer,
authority, and additional sections. since it's optional in the protocol,
it counts as a waste if it causes the TC bit to be set ("truncation occurred")
and a TCP retry to be done.
we could simply stop copying the question section at all. (loses information.)
or we could make it an obscure configuration option. (one of many, it seems.)
or we could try an adaptive strategy: if truncation occurs while building a
response, then try it again with an empty question section, and if truncation
still occurs, then give up and set the TC bit.
i'm in favour of that last approach. anybody else got strong views on it?
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