Mac OS X Network Problem: Slow Remote Login (SSH): FixedFiled on Feb 3, 2008 by AnthonyDiSante
Sometime over the past few months, it started to take a really long time to SSH into my Mac Mini from my Linux system. They’re both on a 100 megabit LAN, but from the time I’d type "ssh user@mini" on my Linux system, it took exactly 30 seconds for the "Welcome to Darwin" message to appear. So obviously it was waiting for some kind of timeout to expire.
The fix was to edit the /etc/hosts file on the Mac Mini and add a line for the Linux system; now logging in via SSH is instant. So it looks like the Mini was for some reason trying to do a reverse DNS lookup on the incoming IP, and timing out since I’m not running a local DNS server. Various websites suggested disabling IPV6 on the Mac, but that didn’t help.