EDNS packet sizes

[Howard Wilkinson]

I am coding up some software that will attempt to use EDNS queries 
against the name servers it is interrogating. I was wondering if the 
strategy of setting the maximum packet size to 65k would promote any 
failures in the target name servers or the pathways to them that a 
smaller packet size may not?

I know some servers will fail to respond to EDNS and am coping with that 
already, but I am trying to work out whether I need to do packet size 
discovery in my code or can I leave this to the name servers MTU 
discovery process in all cases.

I understand that firewalls in the pathway may also cause problems, but 
again will the servers cope or do I need to try something like a binary 
chop discovery mechanism.

Regards, Howard.