Figure 2: Graceful Routing Engine Switchover Process - Juniper EX9200 Features Manual

Chapter 1: Understanding How GRES Enables Uninterrupted Packet Forwarding During a Routing Engine Switchover
Copyright © 2017, Juniper Networks, Inc.

Figure 2: Graceful Routing Engine Switchover Process

When a switchover occurs, the switchover process is as follows:
When keepalives from the master Routing Engine are lost, the system switches over
1.
gracefully to the backup Routing Engine.
The Packet Forwarding Engine connects to the backup Routing Engine, which becomes
2.
the new master.
Routing platform processes that are not part of GRES (such as the routing protocol
3.
process [rpd]) restart.
State information learned from the point of the switchover is updated in the system.
4.
If configured, graceful restart protocol extensions collect and restore routing
5.
information from neighboring peer helper routers.
NOTE: On T Series and M320 routers during GRES, the Switch Interface
Boards (SIBs) are taken offline and restarted one by one. This is done to
provide the Switch Processor Mezzanine Board (SPMB) that manages the
SIB enough time to populate state information for its associated SIB. However,
on a fully populated chassis where all FPCs are sending traffic at full line rate,
there might be momentary packet loss during the switchover.
NOTE: When GRES is configured and the
is executed on a TX Matrix Plus router with 3D SIBs, we cannot ascertain
which Routing Engine becomes the master. This is because the chassisd
process restarts with the execution of the
The chassisd process is responsible for maintaining and retaining mastership
and when it is restarted, the new chassisd is processed based on the router
or switch load. As a result, any one of the Routing Engines is made the master.
restart chassis-control command
command.
restart chassis-control
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