How to Reduce DHCP Polling Time

[neeper67]

I am running Microsoft DHCP, this server has one NIC on VLAN2 and the other NIC on VLAN1.

I have heard there is a way to reduce the DHCP Poll time during a phone boot process.

My phones usually takes between 35-45 seconds to find the DHCP.

I think it has something to do with my Microsoft DHCP options.

[eazeaz]

DHCP Time

Multihoming a DHCP Server on two VLANS?

anyway, the behavior you describe can be caused by spanning tree. Its default setting is usually 30 seconds. The switch port will sit in inactive listening mode for 30 seconds before it will allow any traffic to pass. If this is your problem however, it will not just be phones with the issue. Any computer/device will take a long time to get an address.

Just a thought.

[neeper67]

Thanks, I thought there is a way to change options in Microsoft DHCP to speed up the DHCP process.

[eazeaz]

dhcp

Without spanning tree the process only takes a few seconds.

There isn't anything to speed up.

The switches are blocking the packets, causing the process to be slow. The switches have to be adjusted to speed up the process.

We had a customer with the same problem recently. Disable spanning tree and dhcp took 3 seconds instead of 30. It was actually long enough to cause dhcp timeouts with WDS.

[neeper67]

Ok so it is a switch configurations not a MS DHCP configuration change.

I will disable spanning tree globally and see if it helps

[eazeaz]

Stp

Spanning tree prevents switching loops. It can "hide" problems that may exist in your network.

just keep in mind, that if your network explodes after you disable spanning tree, that you could have a switching loop.

In all likelihood, your dhcp slowness will go away, and you will have no issues. Just make sure you dont disable during business hours just in case.

[cburgy]

You can actually look at the STP status before you disable to see if any ports are in the blocking state.

Note that Shoretel highly recommends (if you are going to use STP) you disable STP on the ports SG switches and server(s) are connected to.

What switching infrastructure do you have?

[neeper67]

We are running 2 stacked Dell Powerconnect 6248P.

I attached a screen shot.

The port state are either Forwarding or Disabled or Manual Disabled.

The role is either Disabled or Designated.

Does this look ok?