Monitoring, Management & Location Tracking

Slow SSH Login Process

Aruba Employee

 PROBLEM :

An SSH connection is slow to log in. The SSH connection to the server is made immediately, the server requests a password, but the time to get the first prompt is 30+ seconds.

 NOTES :

When an SSH connection is made, the sshd process does a reverse DNS lookup on the client. If one of the DNS servers you have configured in /etc/resolv.conf is down or slow to respond, the SSH authentication process will be slow. All DNS servers configured will be queried and *all* must respond.
 

SOLUTION :

Test each DNS server for looking up the SSH client.

# dig @<DNS SERVER> a <CLIENT IP>
# dig @<DNS SERVER> a <CLIENT HOSTNAME>

Remove any DNS server that is not responding.

An alternative solution is to edit the sshd configuration file and remove the DNS lookups during authentication.

# vi /etc/ssh/sshd_config

Find the line "#UseDNS yes" and uncomment it if necessary. Replace that line with:

UseDNS no

Save the file and restart sshd using:

# service sshd restart

Version history
Revision #:
1 of 1
Last update:
‎06-29-2014 07:58 PM
Updated by:
 
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