Hi,

I have NEC DT 700 phones, First these were working fine and obtaining IPs through Windows DHCP server, next day they they just giving message "connecting DHCP" but not outcome.

Phones are connecting through Cisco switch, we enabled CDP on both phone and Switch. All the vendor specific option configured perfectly on DHCP, as I told first working without no issue, when I debug DHCP packets, I find phones are not sending any DCHP query but phon's LCD shows connecting DHCP, any one have idea or face same issue, please share it with me.

The DT700 phones do not supposed CPD as far as I know, and will only attempt to listen for LLDP packet information. Does your switch support LLDP?

I had this problem at a customers' site a while back. His DHCP Scope options were wrong as well.

1. DT700 Supports CDP
2. Cisco switch does not support LLDP
3. We disabled LLDP and enabled CDP
4. Instead of DHCP option, we used auto config tool to push configuration.
5. Its working on all phones, sometimes, any phone stop communicating.
6. Yesterday, one phone was working, I plugh PC port and disconnect phone port, and re-connnect, since that time, it stopped communicating.
7. I debugged, DHCP, phone is not send any DHCP request,
8. I can see NEC phone in show CDP neighbor as well.
9. Sometime it start working sudden

Hi History,

Not sure of what Cisco switch/image your are using , but our rather old 3750 switches (image 12.2(37)), as well as 3560 switches (image 12.2(44) do support LLDP .

Cisco has been supporting LLDP-MED and following the normalized standard by sending the Network Policy TLV.