SSH hang on expecting SSH2_MSG_KEX_DH_GEX_GROUP

This solved it for me:
http://www.snailbook.com/faq/mtu-mismatch.auto.html

"You probably have an MTU/fragmentation problem. For each network interface on both client and server set the MTU to 576, eg ifconfig eth0 mtu 576"

If 576 doesn't work try 1000.