[nsd-users] Why doesn't UDP cause UDP?

W.C.A. Wijngaards wouter at NLnetLabs.nl
Thu Dec 10 15:47:06 UTC 2009

Hash: SHA1

Hi Paul,

On 12/05/2009 12:58 AM, Paul Hoffman wrote:
> This new rule makes it impossible to start being a slave to a master
> that requires UDP, unless it will do AXFR. That is, even specifying
> "UDP" will not let NSD start be a slave because at first, the serial
> number will be 0. This seems like a pretty severe restriction in the
> name of forced safety.

The UDP keyword allows NSD to use UDP for IXFR attempts.
AXFR and some-IXFR responses cause fallback to tcp in any case.

So, the master does not require UDP, but instead the use of UDP may be
very useful - simply because of lower bandwidth for small changes.  To
my knowledge no masters 'require UDP', although they may allow it.

So with this option NSD will attempt to use the less overhead UDP form
of IXFR update when possible.  When not possible, such as at a start
like you say, or when flagged by the master that the update is large,
then TCP is used.

Best regards,
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