[dns-operations] Minimalistic DNS server for SOA and AXFR

Paul Vixie paul at redbarn.org
Tue Jul 17 14:50:53 UTC 2012

On 2012-07-17 2:26 PM, Anand Buddhdev wrote:
> On 17/07/2012 15:33, Mark Andrews wrote:
>> Actually named does do SOA queries over TCP before AXFR.
> On my MacOS X laptop (which comes with BIND 9.7.3-P3), I didn't see SOA
> queries over TCP. I saw a SOA query over UDP, followed by an AXFR
> request over TCP. Besides TC in a UDP response, what would cause BIND to
> do an SOA query over TCP?

i don't know what bind9 does; presumably no tcp soa queries.

but in bind 4 and bind 8, there was for a long while only a tcp session,
which started with an soa query and then continued (if the serial number
thus received warranted this) to do an axfr. later we added an in-server
udp soa query to forego the fork/exec of named-xfer if the serial number
did not warrant a transfer, but we still made that initial tcp soa query
inside named-xfer, sort of as race-condition avoidance, sort of as we
forgot to remove it from named-xfer when we added it to named.

because bind 8's behaviour in this way was not unreasonable, i think a
python-writ zone transferrer should be able to respond to soa queries
over tcp.


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