Why is SSH so Slow?
I was having a horrendous time logging into one particular Linux server. It would take anywhere from 20 seconds to a minute to let me log in.
Turns out, there are two sshd config settings you should pay attention to:
VerifyReverseMapping and GssAuthentication
The latter only really helps if you are connecting from a Mac (like me). VerifyReverseMapping will tell the server to look up the host name for client IPs, and if the IP you’re SSH’ing from doesn’t have a reverse DNS entry, this will result in a DNS timeout. (The source of most of the delay in logging in.)
So open up your sshd config file: /etc/ssh/sshd_config
Remove VerifyReverseMapping, if it exists. The default value for it is no. If you don’t see it, this isn’t the source of your problem.
Remove GssAuthentication, if it exists. It also, defaults to no.