Title: Error message: "Unable to communicate with client" or "cannot gain network access to client"
Date: 11/06
NV Version: All
OS Version: Unix / Linux / HPUX
Application version: N/A
Plugin version: N/A
Description: This FAQ describes the change needed to resolve the above error message that may be received on Unix / Linux clients. In addition the error message "cannot gain network access to client" may also be seen.
Symptoms: Backups fail with "Unable to communicate with client" and/or "cannot gain network access to client". There may also be many instances of "Machine 'xyz' has gone down" and "Machine 'xyz' has come up" in the logs.
This issue may be down to a badly configured /etc/nsswitch.conf file. This file is used by Unix / Linux networking to determine the order in which to attempt name resolution. The first method that works causes the search to stop. Methods that are not active should be demoted to the end of the line so they are not attempted.
The most common 3 methods that may be listed on the "hosts:" line are:
nis
files
dns
nis: This is the Network Information Service and is not widely used on modern networks files: This instructs the networking stack to try name resolution by parsing the /etc/hosts file dns: This is the Domain Name Service and is the most common form of name resolution.
Depending on the exact OS the line may read differently from the example below but the concept of the change is the same.
On a default install of HPUX the "hosts:" line in /etc/nsswitch.conf will read:
hosts: nis files dns
If the NIS service (Network Information Service) is not active on the network then this may cause the problems outlined above. The "nis" option should be demoted to the end of the line (or even removed) so that the active methods of name resolution (files and dns) are used in preference. So in our example the line will now read:
hosts: files dns nis
Now the local /etc/hosts file will be interrogated first with DNS checked if name resolution is not achieved with the local hosts file.
