VLAN – Cisco Voice VLAN DHCP Not Working

vlanvoice

Having an issue with a voice vlan setup but only on my Cisco stack, Brocade stack works.
DHCP is on VLAN5 (for phone and pc) using Option 156 for voice
VOIP is on VLAN100

Shoretel Phone1 and PC1 on the Brocade

 dual-mode  12
 no cdp enable
 inline power
 voice-vlan 100
 trust dscp

Shoretel Phone2 and PC2 on C9300

 switchport access vlan 12
 switchport mode access
 switchport voice vlan 100
 auto qos trust cos
 no cdp enable

I believe they are basically the same in configuration:

Trunk Vlan 100 (tagged)
Native vlan 12 (untagged)

I am unable to get DHCP on Phone2, PC2 works.

Any ideas?enter image description here

Best Answer

Cisco switches use CDP (default) or LLDP to negotiate a trunk with a phone acting as a switch on an access interface. Since you are using non-Cisco phones, you must either enable LLDP (if your phone supports that), or you will need to configure the switch interface as a trunk.

To globally enable LLDP:

lldp run

Then, on each interface:

lldp transmit
lldp receive

Or, for a trunk on the interface:

switchport trunk allowed vlan 12,100
switchport trunk native vlan 12
switchport mode trunk