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Cisco DHCP, Polycom 450, and voice VLAN issues

DHCP server running locally on a 2960 switch. Polycom 450 phone trying to get an IP in the VoIP VLAN.

When the switchport configuration is set for an access port in the voice VLAN, the phone gets an IP and all is well.

When the switchport configuration is set to auto negotiate the voice VLAN, the phone does not get and IP address. The DHCP server behaves differently and although it sees the DHCPREQUEST come back, it decides to find a relay rather than sending a DHCPACK.

This started off with me troubleshooting a Windows DCHP scope - same symptoms, then I deactiveated  the scope and built the DHCP server on the core switch, same symptoms, and finally, I moved the DHCP service to the same switch as the phone.

I tried both LLDP and CDP for VLAN negotiation. Both seem to place the phone correctly in the VoIP VLAN. I stopped and started the DHCP service.

The phone vendor is insistent that the issue is not with the phones and I tend to agree having deployed the same phones on Cisco switches serveral times.

Attached is the DHCP, switchport info, and DHCP packet and UDP traffic debug for the phone after the phone has been power cycled. Thank you for reviewing!






HiI am interested on the same


I am interested on the same.

I didn't have long experience with VoIP, but lucky or by chance my short experience have been completely Cisco, really it work well.
Less than a month ago I had a project with mixed brands (Cisco 1921 Router, Small Switch Cisco Cisco SG200-50P, Cisco and Polycom IPhones.

Today I think I have been lucky with this switch, because it have templates and wizards for VoIP VLAN, I disabled the smart ports features because I feel this like an unexpected behavior, I changed the detection method for Voice VLAN following the OUI, I added the Polycom OUI and today it is working well, all ports can be VLAN 10 (data) or VLAN 20 (Voice VLAN).

I tried to trick port changing workstations MAC Address on Windows, following the Polycom OUI, and the switch can not be fool, I guess is for LLDP.

But, how I can control or modify LLDP params?

What happen in a mixed environment?

The answer

The answer