Bind - OPT UDPsize=1232 ?

Karl Pielorz kpielorz_lst at
Tue Jun 1 14:01:14 UTC 2021

--On 1 June 2021 at 13:03:12 +0200 Anand Buddhdev <anandb at> wrote:

> On 01/06/2021 12:55, Karl Pielorz wrote:
> Hi Karl,
>> Anyone know why the Bind query appears to set such a low UDPsize? -
>> We've nothing in our config setting sizes, or maximums.
> Here's an answer:
> Regards,
> Anand


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.

Even more annoyingly - all the 'flag day' / online test sites we can find - 
it works with, and passes all the tests.

Which means even if there were a chance of getting the remote server fixed 
it's going to get "well, it works everywhere else and the online tests say 
it's a pass..."

Thanks again though,


More information about the bind-users mailing list