User's Manual

6 Configuring a Wireless Backhaul
128 Installation and Configuration Guide: Airgo Access Point
Use of Radios for Backhaul
Each access point in a backhaul configuration must have two radios and be enrolled in the network.
One of the radios operates in normal mode to serve downstream APs or clients. The other radio
assumes the backhaul role (BP), relaying network traffic from clients or other APs through the
backhaul arrangement up to the wired network. Each radio operates in a different band.
For a backhaul point radio to establish a link with an AP, it must be able to receive its radio signals.
Accordingly, the AP node with the BP radio must be within range of the upstream AP radio. A
radio can be configured to operate in the BP mode even if its node is directly connected to the wired
network, as in the case of building-to-building bridge applications.
From the perspective of the wired APs, each backhaul AP appears as a client; however, these
“clients” are not identified in the RADIUS user database. For authentication purposes, identity
information for the backhaul APs is automatically entered into the internal RADIUS database on
the security services portal AP upon enrollment of the backhaul node. Users cannot view or modify
this information.
Wireless Backhaul Trunks
A trunk is a wireless connection from one access point radio to another. An access point that is not
connected to the wired network or an access point explicitly configured in the BP mode tries to
establish a wireless trunk connection to another access point. A succession of trunks established
between access points provides a path from client stations through the wireless network to the
wired network.
If a trunk connection fails or a backhaul link goes down, then the access point that established the
trunk re-scans the wireless environment and attempts to connect to another AP radio with
compatible wireless and network characteristics. This process is called retrunking.
Backhaul retrunking usually occurs quickly (2-3 seconds) if uplink candidates are available.
Subnets do not change as a result of retrunking. If a backhaul trunk fails and the BP radio cannot
reestablish (recover) backhaul within 30 minutes, all backhaul links formed with its uplink AP
radio are brought down. This gives an opportunity for the downlink nodes to attempt to form
alternate backhaul paths.
Wireless Backhaul security
After enrollment, the BP radio uses WPA (EAP) for authentication and AES for encryption on its
trunk or trunks. The following security restrictions apply:
• The upstream AP must have WPA enabled.
• All WPA-compatible authentication and encryption schemes are permitted.
• WEP may be enabled in addition to WPA on the upstream AP
• Both upstream and downstream APs must be enrolled by NM Portal.
For more information on security, see Chapter 7, “Managing Security.”
NOTE: The access point must have a wired connection to be enrolled in the network
(see “Enrolling APs” on page 165). After the AP is enrolled, the wired connection can
be removed.