[Pdns-users] How to force recursions to TCP only

[Otto Moerbeek]

Kevin, you're right that there's no option. But blocking UDP in the
firewall isn't going to fly, the recursor only falls back to TCP on
TC=1 (truncated) answers, not on UDP timeout or error.

In general it's a bad idea to force TCP, as it increases load on both
recursor and authoritative servers. Better fix your UDP connectivity.

	-Otto


On Fri, Feb 28, 2025 at 09:10:59AM -0500, Kevin P. Fleming via Pdns-users wrote:

> I don't think there are any configuration options in the recursor do to this, so you'll have to do it in a firewall system outside of the recursor. Blocking all outbound traffic to UDP port 53 would take care of it.
> 
> On Fri, Feb 28, 2025, at 06:45, Carlos N via Pdns-users wrote:
> > Hello all
> > 
> > I,m looking for a way of forcing all outgoing queries from recursor to authoritative servers to be TCP.
> > I'm experiencing some packet discards in my platform internal network and i think forcing to TCP may help overcome some of the problems caused by discards.
> > Does anybody know how to do this or if it is even possible.
> > Documentation doesn't give any clue.
> > Kind regards and thanks in advance.
> > 
> >      Carlos
> > 
> > 
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