Thanks for your appreciated replies!
I do not think this is a firewall issue because when using `dig` command I get no issues. Tried with two different sets of options: * `dig +bufsize=512` : got `Truncated, retrying in TCP mode` then a correct reply received through TCP * or simple `dig` : in that case I directly get the answer through UDP
But of course it does not work when disallowing TCP retry mode and setting a 512 bytes buffer size (`dig +bufsize=512 +ignore`)
Tests show clearly now a limit based on packet size (512 bytes) but I still do not know where it comes from precisely. Will investigate deeper when I will have some time.