Nortel Networks NN47250-500 Distributed APs and STP, Distributed APs and DHCP option 43

Nortel WLAN—Security Switch 2300 Series Configuration Guide

Distributed APs and STP

A Distributed AP is a leaf device. You do not need to enable STP on the port that is directly connected to the AP.

If Spanning Tree Protocol (STP) is enabled on the port that is directly connected to a AP, you might need to change the

STP configuration on the port, to allow the AP to boot.

As part of the boot process, an AP disables and reenables the link on the port over which the AP is attempting to boot. If

STP is enabled on the device that is directly connected to the port, the link state change can cause the port on the other

device to leave the forwarding state and stop forwarding traffic. The port remains unable to forward traffic for the

duration of the STP forwarding delay.

An AP waits 30 seconds to receive a reply to its DHCP Discover message, then tries to boot using the other AP port. If

the boot attempt fails on the other port also, the AP then reattempts to boot on the first port. The process continues until

a boot attempt is successful. If STP prevents the other device’s port from forwarding traffic during each boot attempt, the

AP repeatedly disables and reenables the link, causing STP to repeatedly stop the other device’s port from forwarding

traffic. As a result, the boot attempt is never successful.

To allow an AP to boot over a link that has STP enabled, do one of the following on the other device:

• Disable STP on the other device’s port.

• Enable the port fast convergence feature, if supported, on the other device’s port. (On some vendors’ devices, this

feature is called PortFast.)

• If the other device is running Rapid Spanning Tree or Multiple Spanning Tree, set the port into edge port mode.

The option 43 field in a DHCP Offer message can provide a simple and effective way for APs to find WSSs across an

intermediate Layer 3 network, and is especially useful in networks that are geographically distributed or have a flat

domain name space. You can use the DHCP option 43 field to provide a list of WSS IP addresses, without the need to

configure DNS servers.

To use DHCP option 43, configure the option to contain a comma-separated list of WSS IP addresses or hostnames, in

the following format:

You can use an IP address list or a hostname list, but not both. If the list contains both types of values, the AP does not

attempt to use the list.

The ip and host keywords can be in lowercase, uppercase (IP or HOST), or mixed case (example: Ip, Host, and so on.)

You can use spaces after the colon or commas, but spaces are not supported within IP addresses or hostnames. Leading

zeroes are supported in IP addresses. For example, 100.130.001.1 is valid.

Note. STP on a port directly connected to a Distributed AP can prevent the AP from

booting.