Issue/Introduction

This article describes how to troubleshoot a slow SSH connection to a VM instance when the network is normal. It applies to the initial diagnosis and resolution of similar issues in ZStack Cloud.

Environment

• Product: ZCF
• Component: Cloud
• Version: 3.x-5.5.30

Symptoms

When the network is normal, establishing an SSH connection to the VM instance is slow.

Possible causes

Possible causes include:

• SSH reverse DNS lookup is enabled, and the lookup takes a long time.
• GSS, or Generic Security Services, authentication is enabled, and authentication takes a long time.
• NSS, or Name Service Switch, name resolution takes a long time.

Resolution

1. Disable SSH reverse DNS lookup.

Run the following command and change the setting to disable SSH reverse DNS lookup:

  [root@localhost~]#vi /etc/ssh/sshd_config
  # Edit sshd_config and change the following setting
  UseDNS=no

2. Disable GSS authentication.

Run the following command and change the setting to disable GSS authentication:

  [root@localhost~]#vi /etc/ssh/sshd_config
  # Edit sshd_config and change the following setting
  GSSAPIAuthentication no

3. Modify nsswitch.conf on the VM instance.

Run the following command and change the setting in nsswitch.conf:

  #vi /etc/nsswitch.conf
  # Edit nsswitch.conf and change the following setting
  hosts: files