Cisco UC500 series Configuration Manual page 18

4.3.9 Click on the "Device Configuration" tab on the right pane & do the below:
Domain name: name the provider requires the UC500 to have
Enable Domain Lookup: should be checked
Remove any old DNS servers in the config
New Server: Enter IP address of DNS server & click Add
Click "OK" at the bottom to continue
Figure 4.3.9 updated DNS settings for UC500
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