Determine DNS or Connectivity Issues
If the phone continues to reset, follow these steps to eliminate DNS or other connectivity errors:
Procedure
Step 1
Use the Reset Settings menu to reset phone settings to their default values. See the Cisco Unified IP Phone
Reset or Restore, on page 92 for details.
Step 2
Modify DHCP and IP settings:
a) Disable DHCP. See the Configuration Menus, on page 35 for instructions.
b) Assign static IP values to the phone. See the Configuration Menus, on page 35 for instructions. Use the
same default router setting used for other functioning Cisco Unified IP Phones.
c) Assign a TFTP server. See the Configuration Menus, on page 35 for instructions. Use the same TFTP
server used for other functioning Cisco Unified IP Phones.
Step 3
On the Cisco Unified Communications Manager server, verify that the local host files have the correct
Cisco Unified Communications Manager server name mapped to the correct IP address.
Step 4
From Cisco Unified Communications Manager, choose System > Server and verify that the server is referred
to by its IP address and not by its DNS name.
Step 5
From Cisco Unified Communications Manager, choose Device > Phone > Find and verify that you have
assigned the correct MAC address to this Cisco Unified IP Phone. For information about determining a MAC
address, see the MAC Address for Cisco Unified IP Phone Determination, on page 29.
Step 6
Power cycle the phone.
General Troubleshooting Information
The following table provides general troubleshooting information for the Cisco Unified IP Phone.
Table 19: Cisco Unified IP Phone Troubleshooting
ExplanationSummary
Cisco does not support connecting an IP phone to another
IP phone through the PC port. Each IP phone should
directly connect to a switch port. If phones are connected
together in a line (by using the PC port), the phones will
not work.
Connecting a Cisco Unified IP Phone to another
Cisco Unified IP Phone.
A prolonged Layer 2 broadcast storm (lasting several
minutes) on the voice VLAN may cause IP phones to reset,
lose an active call, or be unable to initiate or answer a call.
Phones may not come up until a broadcast storm ends.
Prolonged broadcast storms cause IP phones to
reset, or be unable to make or answer a call.
Cisco Unified SIP Phone 3905 Administration Guide for Cisco Unified Communications Manager 8.6 (SIP)
89
Troubleshooting and Maintenance
General Troubleshooting Information
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