As for other authoritatives, BIND should support the
cookies AFAIK. But
I haven't tried.
BIND 9.11 does which is due to be released within the next weeks. I'm
testing BIND 9.11b3 internally but unfortunately not on a public
reachable IP address. I also have a BIND 9.11b3 host as a resolver
configured. "bad cookie" responses are logged in the "resolver" log
category. So, I'm not sure the following auth. servers are good
candidates to test your code ;-)
85.195.97.250
2a01:7480:1:100
89.25.242.242
185.60.169.2
193.93.22.133
Daniel