Windows DHCP issues on startup when connected to Cisco IP Phone

Unanswered Question
Jul 17th, 2009

We are experience random problems, when booting Windows PC's connected to Cisco IP Phones 7911: the PC is unable to get an IP address of the DHCP server.

If, after the PC finishes booting up, we perform an "ipconfig renew" the PC is able to get an IP address from the DHCP server.

The DHCP server is the Catalyst 6500 core switch-router, and when the PC is booting up we see no DHCP request reaching the Catalyst 6500.

We have no problems when the PC is directly connected to the access switch (Catalyst 3560), instead of being connected through the Cisco IP Phone.

The IP Phones configuration, on the CallManager, have the "Forwarding Delay" set to disabled.

Here is the configuration of the switch port:

interface GigabitEthernet0/x

switchport access vlan 10

switchport mode access

switchport access vlan 4

priority-queue out

mls qos trust device cisco-phone

mls qos trust cos

spanning-tree portfast

It seems as if the Cisco IP Phone internal switch is not implementing Spanning-tree PortFast functionality on the 10/100 PC port.

Anyone has seen this happen?


I have this problem too.
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kraghavansag Fri, 07/17/2009 - 09:48


Assuming your voice vlan is 4, is it switchport access vlan or voice vlan 4?


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