The network is normal but SSH connection to the virtual machine is slow. How do I resolve this?

Symptom

SSH connection to the virtual machine is slow even though the network is functioning normally.

Cause

Possible causes include the following:

• SSH reverse DNS lookup is enabled. This lookup process takes a significant amount of time.
• GSS (Generic Security Services) authentication is enabled. This authentication process takes a significant amount of time.
• NSS (Name Service Switch) name resolution is slow.

Solution

1. Disable SSH reverse DNS lookup.

   Run the following command to disable SSH reverse DNS lookup:

   [root@localhost~]#vi /etc/ssh/sshd_config
   # Enter sshd_config edit mode and modify the following setting
   UseDNS=no

2. Disable GSS authentication.

   Run the following command to disable GSS authentication:

   [root@localhost~]#vi /etc/ssh/sshd_config
   # Enter sshd_config edit mode and modify the following setting
   GSSAPIAuthentication no

   When the GSS authentication method is set to gssapi-with-mic, every SSH connection to the virtual machine performs GSSAPI authentication, which takes a significant amount of time. Disabling GSS authentication improves SSH connection speed.

3. Edit the virtual machine nsswitch.conf file.

   Run the following command to edit the virtual machine nsswitch.conf file:

   #vi /etc/nsswitch.conf
   # Enter nsswitch.conf edit mode and modify the following setting
   hosts: files