The phone fails to register

The most common issue with a failure to register is basic connectivity to the phone.

You can check basic connectivity in a number of ways:
  • Obtain the host IP by looking at the phone registration status, configuration file, DNS, and Lync Computer Client Configuration Information Screen.
  • Make sure the phone can communicate with the server by performing a diagnostic ping.
  • From a computer connected on the same network as the phone, perform a telnet to the Lync server SIP TCP port 5061 or 443.
  • Check for a DNS issue.
  • Check if Lync Services is temporarily out of service, for example, a firewall or routing problem with the network.

Check that the phone is reading the configuration files. On the phone, go to Status > Platform > Configuration. The phone displays the current configuration and files. If the phone is not reading the correct configuration files, redo the provisioning procedures. If the phone is reading the configuration files, go to the next troubleshooting tip.

If the phone still cannot register, check autodiscover:
  • Ensure the SRV Record exist and points to a valid A record.
  • Ensure that the A record points to a valid host IP.
  • Use the shell command dnsCacheShow to display a cached DNS entry. If an entry has a negative cache, the phone is trying to perform a lookup and is failing to resolve.

If you get a TLS error, you may have an untrusted, corrupted, or expired certificate. Check if a root CA is installed on the phone by going to Settings > Advanced > Administration Settings > TLS Security > Custom CA Certificate. If you need to troubleshoot TLS, use log.level.change.tls=0 and l og.level.change.sip=0 to log for TLS problems.

Check for invalid user credentials. Use log.level.change.tls=0 , log.level.change.sip=0 , and l og.level.change.dns=0 to troubleshoot authentication failures.

Log into a computer Lync client with a user's credentials and ensure that the user account logs in. Use a simple password for testing purposes.