Troubleshooting DNS problems and Name Resolution issues


Server not able to communicate with the Client machine to perform the backup.

Backup fails with any of the following error messages:

  • 'Client name': Couldn't look up the name of address:'Backup_server_IP':node name or service name not known.
  • Host name for IP address <IP_address> could not be determined through DNS
  • Warning, cannot resolve host <hostname> to <IP address>, name server may be misconfigured.
  • IP address for host '<host>' could not be determined through DNS.
  • Error "Request timed out"



All NetWorker versions

All Avamar version

All BRM versions (Backup & Recovery Manager)

All DPA versions (Data Protection Advisor)



• Hardware or LAN/WAN problems.

• DNS server problems.

• A machine got moved from one VLAN to another but kept its old settings.

• Host files have wrong entries,

• Local machine has old DNS settings in cache and has not updated itself.

• Authentication method on both NetWorker server and client was changed to oldauth.

• Settings in the firewall, or DNS, or ACL have been changed.


Run the following 3 steps:

1) Reboot the machine having the problem.

2) Check the Drivers and the status of your network hardware and connection.
3) From the command prompt type IPCONFIG to verify that the IP address is valid in your local network. If you get a 169.x.x.x IP address then it cannot find a DHCP server to get a valid IP Address. There are many causes for this but most likely it is:

• A network cable gone bad or damaged

• A NIC not working or not supported by your OS

• The signal strength is not good


If everything is fine then do these 16 Checks:


Check 1 - Ping the "DNS Server" from the local machine. PING using its "Long Name" and "Short Name" just to verify both work. Then ping using its IP Address to verify if IP works but Name does not. (verify which DNS Server this location is using then see Check 10)


Check 2 - Ping the Server from the Client then the Client from the Server. PING using its "Long Name" and "Short  Name" in both directions. Then PING using the IP Address of each machine to verify if IP works but Name does not.


Check 3 - Ping GOOGLE.COM just to verify your connection outside your building.


Check 4 - If you use a HOSTS File, update the HOSTS file with the correct IP Address and Host Name. Include the Long Name, Short Name and IP in the HOSTS file.


Check 5 - In the DNS Server, enter long name (FQDN) and also the short name so that it resolves to the same IP Address for the Server and Client.


Check 6 - In the DNS Server, both forward and reverse lookup need to work.


Check 7 - If your DNS is NOT dynamically assigned you will need to manually enter correct values in your network properties.


Check 8 - If your DNS is dynamically assigned and you access a Client or Server (or any host) by using a name other than its DNS host name, a DNS Alias record is needed.


Check 9 - Check the Network Connection Settings in the OS to verify if someone put a 'static' IP in or told it to not to "Automatically Obtain an IP address". If you use a "Static IP" make sure it is a valid IP in LAN or VLAN.


Check 10 - Configure DNS settings in Network Connection Settings in the OS on the local machine.


Check 11 - Set firewall rules to allow inbound and outbound TCP packets both to-and-from the Service ports. Set the connection port and service port range for a server, client, or node.


Check 12 - Check any local network settings such as access control list (ACL), virtual local area networks (VLAN's).


Check 13 - Clear DNS Cache using the commands below for Windows:

Check 14 - Test to verify if your NIC is active and if DNS is working using tracert and nslookup

Check 15 - Verify that the "Name to Address" resolution is correct. Test by running nslookup using the fully qualified domain name of the computer. On Windows, this verification also can be performed from the Network control panel.


Check 16 - Verify that sessions can be established and portmapping is correct.  For "NetWorker" use: rpcinfo -p hostname.


For additional information on how to flush the DNS Cache, re-register with DNS, tracert and nslookup (check 15) please refer to KB 125514.