DF-Flag on UDP-based sockets?

[Borja Marcos]

> On 30 Nov 2022, at 08:20, Tom <lists at verreckte-cheib.ch> wrote:
> 
> Hi list
> 
> Regarding ARM 9.18.9 (https://bind9.readthedocs.io/en/v9_18_9/reference.html#namedconf-statement-edns-udp-size):
> "The named now sets the DON’T FRAGMENT flag on outgoing UDP packets."
> 
> Tested with BIND-9.18.9, I didn't saw any UDP packets, where the "DF"-flag was set on the IP header (true for TCP, but never seen for UDP).
> 
> Which circumstands or which queries enforces BIND9 to set the "DF"-flag on outgoing UDP-based packets?

I have checked on FreeBSD 13.1 and indeed I don’t see the flag. Neither for UDP queries or responses. 

What OS are you trying? Might be OS dependant. 





Borja.