+
+After the correct challenge replies are recieved, both ends have proved
+their identity. Further information is exchanged.
+
+client ACK 655 12.23.34.45 123 0
+ | | | +-> options
+ | | +----> estimated weight
+ | +------------> IP address of server as seen by client
+ +--------------------> UDP port of client
+
+server ACK 655 21.32.43.54 321 0
+ | | | +-> options
+ | | +----> estimated weight
+ | +------------> IP address of client as seen by server
+ +--------------------> UDP port of server