cisco sg200 voice vlan dhcp issue

[ruchiran83]

i have cisco sg200 50p connected to cisco 3750 switch. i just wanted to separate voice (vlan2) and data (vlan1) VLANS. I created vlan 2 as my voice VLAN and separate dhcp server for vlan 2 to give ip addresses to phones. however the ip phone connected to my voice vlan (vlan 2) is not receiving ip address from my dhcp server in vlan 2.

the dhcp server is connected to 3750 switch with an access port (vlan2-voice)

two switches are connected via trunk ports and allowed vlan 1&2

ip phone is connected to sg200 via access port (vlan 2) - 

note - there is no pc connected to ip phone

I really appreciate if anyone can help me with this issue

[Tom Watts · Accepted solution]

Hi Ruchiran,

To cover the basis, ensure the VLAN 2 is added to VLAN database on the 3750. Simple using command "show vlan id 2", if it's not found, then you first need to create the VLAN 2 on the 3750.

Second, if you connect the same IP phone directly to the 3750 on an access port, vlan 2 untagged, does the phone receive IP address as you expect?

Next, on the 3750 trunk connecting to the SX200. When building the trunk use a command like "switchport trunk allowed vlan remove 1-4094" then build the trunk specifically with the VLANS "switchport trunk allowed vlan add 2" which will tag VLAN 2 to the port.

On the SG200 switch, the trunk should be defined and VLAN 2 tagged on the port connecting to 3750 then the port connecting to the telephone should be VLAN 2 untagged as access port.

[ruchiran83]

Hi Tom

Thank you for the support. The phone is now getting the IP from the DHCP on its own VLAN (vlan2 )  according to  your configuration. However i need to configure the auto voice VLAN based on OUI feature which is in SG200 switch. 

The problem is, the switch not allowed me to configure auto voice vlan feature when the port connected to IP phone is in ACCESS mode (it has to be a trunk). I know according to cisco catlyst guidelines this is totally incorrect bcz they say  "Voice VLAN is only supported on access ports and not on trunk ports, even though the configuration is allowed"

I think its not valid for Small business switches . Anyway, when i make the said port  TRUNK it works (by assigning 1U & 2T- automatically).But the phone does not  get an IP address from my DHCP server then. 

Can you help me with this if I am missing some configuration. Thank you once again

[Tom Watts · Accepted solution]

Hi Ruchiran, this will depend on the IP phone. How it sounds to me, the phone is not sending tag packet on the VLAN 2, therefore the untag packet is working on the switchport connecting to the phone.

What model phone are you using? Does this phone support VLAN tag, and if so, can you manually configure the phone for VLAN 2 tagged for testing purpose? Also, if the phone is expected to use a tag packet for voice, it means you should ensure the "pc to phone" feature is enabled as the data VLAN connection would be untagged through the phone's own internal switchport.

The telephony OUI may not be the best feature, I think it may be better to use a auto voice policy with LLDP-MED or CDP on the SG200 if your phone does support it. If not, the telephony OUI is the last choice I'd go with before manually configuring the phones.

[ruchiran83]

Hi Tom

Thank you for the support. Everyting is working fine now. I checked the phone settings and found VLAN tagging option (changed it to 2). Then everything started working.

Once again thanks for the support