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LLDP VLAN tagging not working

Occasional Visitor

LLDP VLAN tagging not working


I have a 2610-48-PWR configured with LLDP to set the VLAN for Polycom IP phones:

vlan 1    

   name "DEFAULT_VLAN"   

   untagged 1-48   

   ip address   

   tagged Trk1    


vlan 20

   name "VOIP"

   tagged 1-48,Trk1




DHCP address for VLAN 20 are given out by the phone system. DHCP address for VLAN 1 are given out by two Windows DHCP servers. In all cases when a PC is connected it is put on VLAN 1 and gets a valid IP address for that subnet. When phones connect they usually get tagged for VLAN 20 and get a correct IP address for the VLAN 20 subnet, But, sometimes a phone gets an IP address from VLAN 1 but is tagged VLAN 20.


It seems that as the phone boots it starts out on VLAN 1 and then eventually switches over to VLAN 20. If the VLAN 1 DHCP server responds before the phone switches to VLAN 20 then the phone gets an invalid IP (VLAN 1) address. This issue started when I upgraded one of the VLAN 1 DHCP servers to Windows 2012 R2. It was never an issue with older version of Windows DHCP server.


Any idea? I tried configuring the new Windows DHCP server to have a delay but that didn’t solve the problem.


Thank you.

Honored Contributor

Re: LLDP VLAN tagging not working

Is the Windows DHCP server patched to a switchport on this same switch?

Occasional Visitor

Re: LLDP VLAN tagging not working

No, the DHCP server is connected to a different switch.

Frequent Advisor

Re: LLDP VLAN tagging not working

The phone should boot until it starts the LLDP-MED service, then it should discover the Voice VLAN and tag it. The switch should then also see that the connected device is classified as a phone. After that, the phone will reach only the VLAN 20 DHCP server. 

That it gets a VLAN 1 IP means, that the LLDP-MED "conversation" isn't working fast enough. Then the phone will boot, not tag any VLAN and get the VLAN 1 IP. After that, the phone will probably start LLDP-MED and get the VLAN tag, but no new IP. 

It is difficult to determine where the error is. Every support will tell you to first upgrade your devices to the newest firmware, so you should do that ;) 

As a workaround, you could look into DHCP options in VLAN 1, directed to the phones with the correct VLAN tag.