Ivorde Unix/Linux/Database/Web/Mail Forum

How to disable ssh daemon reverse IP lookups for clients.

By default, sshd will do a ptr lookup for the IP where a client connects from. If the DNS server fails to respond, sshd (or at least older versions) will hang for a long time and most clients will timeout.

Detecting your ssh version:



If your version is more recent (above4), you can disable ssh reverse lookups by uncommending or adding the following line to sshd_config file:


Otherwise, if ssh version is 3 (not the protocol, but software version), uncoment the following line in the same file:


SSH daemon needs to be restarted so the changes can take effect.

If there are still problems (slow password prompt when ssh to the server), you can start sshd in debug mode:

and attempt to ssh again.

Most probably, the delay will be in the same time with:


This means that there could be problems with the dns servers. Commenting out everything in /etc/resolv.conf will solve the issue.

For the DNS reverse lookup,
Just visit this site http://dnstools.ivorde.ro
It has the best information of IP address, IP address to domain, domain name to IP,domain name, hosting, and ping test to know the particular connection is online or not!!!!!