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DHCP Issue with Procurve Switch 4108gl and Tagged Vlan

Harold Stokes
Occasional Visitor

DHCP Issue with Procurve Switch 4108gl and Tagged Vlan

I am having a issue with a customers 4108gl switching passing dhcp packets. The switch is configured as a Layer 2 switch only. The default vlan is configured as untagged on all ports and a new vlan of 2 has been created for Nortel ip phones and the ports are tagged for this vlan. A Cisco router is used for L3 and the DHCP server is on the default vlan. Since this is the case the ip helper-address command has been configured on the Cisco router to forward the dhcp request to the dhcp server. If the IP phone is given a static IP address for Vlan 2 it works fine and the PC plugged into the back of the phone works fine on Vlan 1. This confirms that Dot1q trunking between the IP sets and the HP Procurve is working properly. However, if we attempt to us DHCP the phone is unable to get a IP address. If we change the port the phone is plugged into to be no for the default vlan and untagged for vlan 2 (Voice VLan) the phone gets a address from the DHCP server. This confirms that the dhcp server is working properly. Does anyone know why the 4108 wouldn't pass a dhcp request on a tagged vlan port?
5 REPLIES
Steven E. Protter
Exalted Contributor

Re: DHCP Issue with Procurve Switch 4108gl and Tagged Vlan

Passing DHCP is pretty important. It is possible that the switch admin configured the switch to not allow that traffic.

It is possible the VLAN is improperly configured.

I don't hink out of the box that switch is going to block DHCP.

SEP
Steven E Protter
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Harold Stokes
Occasional Visitor

Re: DHCP Issue with Procurve Switch 4108gl and Tagged Vlan

Steven it passes DHCP if I set this port as untagged for vlan 2. However, it doesn't pass dhcp if it is tagged as vlan 2 and untagged for vlan 1 which is how I need the configuration to be.
Leo Katona
Occasional Advisor

Re: DHCP Issue with Procurve Switch 4108gl and Tagged Vlan

Most likely the Nortel IP phone is sending the DHCP requests as untagged frames, even though it is properly tagging the actual VoIP traffic.

If this is the case, configuring the 4108gl's port where the phone is connected as untagged for VLAN1 would cause the DHCP requests to be broadcast directly to VLAN1 instead of being properly relayed through the Cisco router in VLAN2.

An easy way to verify exactly what is happening would be to use a crossover cable to connect the Nortel phone directly to a machine running Ethereal or tcpdump/windump and running a packet trace to check whether the DHCP requests are actually arriving in VLAN2-tagged Ethernet frames or untagged frames.

If the DHCP requests are untagged, the problem lies with the Nortel phone and must be corrected there.
Shiraz Malik
Advisor

Re: DHCP Issue with Procurve Switch 4108gl and Tagged Vlan

Most of the IP phones do not have the tagging enabled by default. You should check the manual of Nortel IP phone and make sure that it is sending the tagged packets.
There is no complexity in this problem and its fairly simple to diagnose.
thanks
Khaled Mohsen
Occasional Visitor

Re: DHCP Issue with Procurve Switch 4108gl and Tagged Vlan

I have Procurve 2600 Switch Connected to a CISCO IP Switch I sat it's IP configuration to DHCP but this switch is not getting any IP.
I even connected it to CISCO Core Switch but having the same problem.

anyone can help?