解決ssh 連線登入問題

3.3 - ssh(1) takes a long time to connect or log in

Large delays (more that 10 seconds) are typically caused a problem with name resolution:

• Some versions of glibc (notably glibc 2.1 shipped with Red Hat 6.1) can take a long time to resolve "IPv6 or IPv4" addresses from domain names. This can be worked around with by specifying AddressFamily inet option in sshd_config.
• There may be a DNS lookup problem, either at the client or server. You can use the nslookup command to check this on both client and server by looking up the other end's name and IP address. In addition, on the server look up the name returned by the client's IP-name lookup. You can disable most of the server-side lookups by setting UseDNS no in sshd_config.

解決的方法, 修改 /etc/ssh/sshd_conf 裡面

UseDNS no

小於 3.7.1 版之前的請改

VerifyReverseMapping no

更早之前的如 2.9.9p2 

ReverseMappingCheck no

* Replaced sshd(8)'s VerifyReverseMapping with UseDNS option.
  When UseDNS option is on, reverse hostname lookups are always
  performed.