Bind - OPT UDPsize=1232 ?

Anand Buddhdev anandb at
Tue Jun 1 14:58:26 UTC 2021

On 01/06/2021 16:01, Karl Pielorz wrote:

Hi Karl,

> Thanks for the pointer - ok, yes I can see it's probably EDNS / Flag day
> related etc. I missed that - probably as it's never caused us an issue.
> Annoyingly a value of 1232 causes a TCP fallback to a server out of our
> control that doesn't do TCP very well.

That is frustrating, of course. If you're able to talk to the server
operator, get them to see value in improving their TCP response.

If it's still causing you problems, you have the option of advertising a
bigger EDNS0 buffer size to that specific server with something like
this in your config:

server a.b.c.d/n {
  edns-udp-size 2000; // adjust appropriately

Read the BIND documentation for details so that you understand this fully.


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