[cisco-voip] voice-VLAN problems between Cat 3500XL and Cisco IP phones?

[Alexander Bochmann]

Hi,

we're currently trying to connect a couple of Cisco IP phones 
to older Cat 3524XL PoE switches. 

The access ports on the switches are configured as trunk, 
with the voice-VLAN as non-native (according to Cisco-docs, 
just configuring the voice vlan doesn't work on the old 12.0WC 
IOS on those switches). 
Voice-VLAN autodetection via CDP works. If we connect other 
devices in the voice VLAN, everything is fine. 
If we connect a Cisco IP phone, DHCP doesn't work. The phones 
just say "DHCP timeout", although a sniffer shows that they 
receive DHCP answers from the server.

Has anyone perhaps run into a similar problem? I'm thoroghly 
out of ideas what to try next...

Alex.