Stateful Line Module Configuration Scenarios; High Availability Configured And Enabled On The Line Module - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - SERVICE AVAILABILITY CONFIGURATION GUIDE 2010-10-08 Configuration Manual

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Stateful Line Module Configuration Scenarios

High Availability Configured and Enabled on the Line Module

Copyright © 2010, Juniper Networks, Inc.
The design architecture used for E120 and E320 routers causes the packets that are
designated for the SC to be first sent to the IC using a direct memory access (DMA)
method. These packets are then forwarded to the SC over the internal 100 Mb Ethernet
channel. Similarly, packets that are destined to be transmitted from the router are first
sent to the IC over the Ethernet channel and then sent from the IC to the FC using a DMA
operation. During the switchover period, until the secondary line module becomes
operational, this communication channel from the IC is not active. The amount of time
taken for the operational image on the secondary line module to start fully functioning
can take up to several seconds. During this period of completion of the switchover process,
applications on the SC handle this timeout. Applications that are impacted by this outage
are routing protocols or protocols that are time-critical. For example, SRP-based TCP
and UDP services are preserved across a switchover, which enables applications, such
as Telnet, FTP, SSH, and SNMP, to operate seamlessly.
When the high availability functionality for line modules is active, subscriber sessions are
maintained whenever a software or hardware fault is detected on the primary line module.
A brief interruption occurs in the subscriber data traffic during the time that the secondary
line module takes over as the primary line module.
Stateful Line Module Switchover Overview on page 68
Guidelines for Configuring Stateful Line Module Switchover on page 70
Stateful Line Module Switchover Platform Considerations on page 70
Replacement of Line Modules When Stateful Line Module Switchover Is Enabled on
page 77
Application Support for Stateful Line Module Switchover on page 79
Stateful Line Module Switchover Modes on page 83
Stateful Line Module Switchover States on page 84
Activating High Availability on page 88
Deactivating High Availability on page 89
The line module high availability functionality is based on the stateful SRP switchover
design architecture, with the implementation extended to two pairs of line modules to
function as the primary and secondary module. This section describes the behavior of
different system functions when line module high availability is configured on the router.
If line module high availability is configured and the state is active, when a fault occurs
on the primary line module, the primary line module performs a warm switchover to a
secondary module. After the switchover, the secondary module starts operating as the
new primary module. The previously configured primary module, after it becomes
operational, takes over the role of the secondary module.
Chapter 4: Managing Stateful Line Module Switchover
75