User Guide

40 Chapter 1 Overview
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• fault tolerance — If a Nortel SNAS 4050 device fails, the failure is detected
by the other node in the cluster, which takes over the switch control and
session handling functions of the failed device. As long as there is one
running Nortel SNAS 4050, no sessions will be lost.
The devices in the cluster can be located anywhere in the network and do not have
to be physically connected to each other. All the Nortel SNAS 4050 devices in the
cluster must be in the same subnet. The cluster is created during initial setup of the
second node, when you specify that the setup is a join operation and you associate
the node with an existing Management IP address (MIP).
For more information about Nortel SNAS 4050 IP addresses, see “About the IP
addresses” on page 51. For information about adding a node to a cluster, see
“Adding a Nortel SNAS 4050 device to a cluster” on page 61.
One-armed and two-armed configurations
The Nortel SNAS 4050 must interface to two kinds of traffic: client and
management. The interface to the client side handles traffic between the
TunnelGuard applet on the client and the portal. The interface to the management
side handles Nortel SNAS 4050 management traffic (traffic connecting the Nortel
SNAS 4050 to internal resources and configuring the Nortel SNAS 4050 from a
management station).
There are two ways to configure the Nortel SNAS 4050 interfaces:
• one-armed configuration (see “One-armed configuration” on page 41)
• two-armed configuration (see “Two-armed configuration” on page 41)
You specify whether the Nortel SNAS 4050 will function in a one-armed or
two-armed configuration during initial setup (see “Initial setup” on page 49).