Graceful Protocol Restart - Dell PowerConnect J-EX4200-24T Software Manual

Graceful Protocol Restart

Redundant Routing Engines
and enabling traffic on the LAN to be routed without relying on a single routing platform.
Using VRRP, a backup J-EX Series switch can take over a failed default switch within a
few seconds. This is done with minimum loss of VRRP traffic and without any interaction
with the hosts.
For more information on VRRP, see "Understanding VRRP on J-EX Series Switches" on
page 1425.
With standard implementations of routing protocols, any service interruption requires
an affected switch to recalculate adjacencies with neighboring switches, restore routing
table entries, and update other protocol-specific information. An unprotected restart of
a switch can result in forwarding delays, route flapping, wait times stemming from protocol
reconvergence, and even dropped packets. Graceful protocol restart allows a restarting
switch and its neighbors to continue forwarding packets without disrupting network
performance. Because neighboring switches assist in the restart (these neighbors are
called helper switches), the restarting switch can quickly resume full operation without
recalculating algorithms from scratch.
On J-EX Series switches, graceful protocol restart can be applied to aggregate and static
routes and for routing protocols (BGP, IS-IS, OSPF, and RIP).
Graceful protocol restart works similarly for the different routing protocols. The main
benefits of graceful protocol restart are uninterrupted packet forwarding and temporary
suppression of all routing protocol updates. Graceful protocol restart thus allows a switch
to pass through intermediate convergence states that are hidden from the rest of the
network. Most graceful restart implementations define two types of switches—the
restarting switch and the helper switch. The restarting switch requires rapid restoration
of forwarding state information so that it can resume the forwarding of network traffic.
The helper switch assists the restarting switch in this process. Individual graceful restart
configuration statements typically apply to either the restarting switch or the helper
switch.
Two to ten J-EX4200 switches can be interconnected to create a Virtual Chassis
configuration that operates as a single network entity. Every Virtual Chassis configuration
has a master and a backup. The master acts as the master Routing Engine and the backup
acts as the backup Routing Engine. The Routing Engine provides the following
functionality:
Runs various routing protocols
Provides the forwarding table to the Packet Forwarding Engines (PFEs) in all the
member switches of the Virtual Chassis configuration
Runs other management and control processes for the entire Virtual Chassis
configuration
The master Routing Engine, which is in the master of the Virtual Chassis configuration,
runs Junos OS in the master role. It receives and transmits routing information, builds
and maintains routing tables, communicates with interfaces and Packet Forwarding
Chapter 1: Software Overview
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