Chapter 1 Reliability Overview; Introduction To Reliability - 3Com 3C13636 Configuration Manual

3Com Router 3000 Ethernet Family
Configuration Guide

Chapter 1 Reliability Overview

1.1 Introduction to Reliability

During communication, any software or hardware error, network device or line fault for
example, may disrupt the connection, causing transmission failure. To avoid these
situations, V 2.41 provides backup center, virtual router redundancy protocol (VRRP)
and hot backup technologies to ensure availability of a backup scheme when faults
occur. This guarantees smooth communication, and makes the network more robust
and reliable.
The backup center provides sound backup functions for the communication lines
between routers. By assigning backup interfaces to an interface and tuning parameters
such as priority and switchover delay of the backup interfaces, you can have the
backup interfaces assume the work of the failed main interface before the ongoing
service is affected. This significantly improves reliability of the lines. In V 2.41, a main
interface can be a physical interface, subinterface or logical channel (such as an X.25
virtual circuit) on an interface; its backups can be dialer-route logical channels or
physical interfaces.
VRRP improves reliability of connections to the outside networks and as such, is well
suited to multicast or broadcast LANs such as Ethernet. Multiple routers can form a
standby group or a virtual router, acting as the only egress gateway for the local
network. These routers, however, are transparent to the local network. In the standby
group, a router is engaged in packet forwarding, a backup router is ready for replacing
the active router, and the other routers are listening. In case the active router fails, the
backup router would take over and the other routers would elect among them a new
backup router. This improves reliability, allowing the local hosts to continue their
operation without any modification.
V 2.41 provides high-end devices with the hot backup mechanism. Usually, a high-end
device achieves redundancy by using two main processing units (MPUs). When the
active MPU fails, traffic automatically switches over to the slave MPU. In addition, hot
backup allows in-service software upgrade, ensuring normal operation of the services.
3Com Corporation
1-1
Chapter 1 Reliability Overview