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voip phone works with hub, but not with switch?

The connection in my office has the following config:

[Catalyst 6509]<---[ip phone 7960]<---[PC]

The 7960 phone got DHCP from voice VLAN. The PC got DHCP from data VLAN.

If I insert a hub between 6509 switch and 7960 phone, everything works fine. (the hub is transparent to the phone and switch).

[Catalyst 6509]<---[Hub]<---[ip phone 7960]<---[PC]

When I insert a Catalyst 2912 switch between 6509 switch and 7960 phone, only the PC can get DHCP on data VLAN. The phone seems lost connection to voice VLAN.

[Catalyst 6509]<---[Catalyst 2912]<---[ip phone 7960]<---[PC]

I have some knowledge about VLAN and trunking. I was wondering if there's any way to make the 2912 switch act like a hub and allow the 7960 phone get into voice VLAN.

Please note: I have NO control of the 6509 switch. I have full control of the 2912 switch.

Thanks in advance.


Re: voip phone works with hub, but not with switch?

Hi Michael,

I believe you have 2912XL switch, please correct me if I am wrong? Is yes I don't think it is capable of supporting voice vlan configuration but it do support multivlan configuration.

We need to find out few things from cat6k switch that whether the port to which IP phone was directly connected is configured as auxillary port for ip phone and access port for data? If yes then I believe if you confiogure 2912XL switch with multivlan port configuration with both the vlans which you have configured on cat6k switch it should work fine.

config t


switchport mode multi

switchport multi vlan vlan-list

Just find out the port on cat6k to which ip phone was connected is been configured for which 2 vlans (for voice and data) and then configure the same vlans in vlan-list in the ablve mentioned command and see if it resolves the isssue.




Re: voip phone works with hub, but not with switch?


Thanks for the reply.

Yes, it's a 2912XL.

On which port shall I configure the multi vlan? The uplink port of 2912XL or the port that connects the ip phone? Shall I leave the uplink port in default vlan 1?

Again, I DO NOT have control of the 6509 switch. I think I can find out the vlan number by using a sniffer. But I am not sure if I can form a trunk between 2912xl and 6509.

So, a hub support multi vlan by default? (stupid question)

Re: voip phone works with hub, but not with switch?

Hey Michael,

HUB does not support and neither understand any VLAN so traffic from any VLAN can pass easily from any port as the HUB ports does not understand any VLAN.

So taking into consideration cat6k is been configured with 2 vlans for for voice and one for data you configure the port on 2900XL switch as multivlan port. Now the port connected as uplink to cat6k and port connected to ip phone both should be configured as multivlan with both the vlans which is configured on cat6k switch.

I hope this should work but just try that and update if it worked.