Skip to Main Content
JUNOS High Availability
book

JUNOS High Availability

by James Sonderegger, Orin Blomberg, Kieran Milne, Senad Palislamovic
August 2009
Intermediate to advanced content levelIntermediate to advanced
690 pages
20h 14m
English
O'Reilly Media, Inc.
Content preview from JUNOS High Availability

Graceful Routing Engine Switchover

Graceful Routing Engine Switchover (GRES) takes advantage of the separation between the control and forwarding in JUNOS software to provide system redundancy. GRES allows the control plane, in this case the RE, to switch over to its backup RE without any interruption to the existing traffic flows in the PFE. When GRES is configured on the router, the kernel state on both REs is synchronized to preserve routing and forwarding state on both REs. Any changes to the routing state on the primary RE result in an automatic incremental update of kernel state on the backup RE. As you can see, the GRES concept is very simple.

However, the limitation of GRES is that, by itself, it cannot provide router redundancy. Even though traffic continues to flow through the router during a switchover between REs, the flow occurs for only a limited time. As soon as any of the protocol timers expire, the neighbor relationship between routers is dropped and traffic is stopped at the upstream router. To maintain high availability, networks must quickly discover when a neighbor goes down and must implement the lowest possible timers. Because GRES provides an intact forwarding plane, it is to our advantage not to drop any of the adjacencies, but rather to continue sending traffic toward the failed router.

The solution to this limitation is to use the Graceful Restart (GR) protocol extension. GR signals all supporting protocols that the failing router is capable of forwarding ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

Network Performance Baselining

Network Performance Baselining

Daniel Nassar
Cisco Catalyst QoS: Quality of Service in Campus Networks

Cisco Catalyst QoS: Quality of Service in Campus Networks

Mike Flannagan - CCIE® No. 7651, Richard Froom - CCIE No. 5102, Kevin Turek - CCIE No. 7284
Juniper Networks® Field Guide and Reference

Juniper Networks® Field Guide and Reference

Aviva Garrett, Gary Drenan, Cris Morris, Juniper Networks®
Juniper Networks® Reference Guide: JUNOS™ Routing, Configuration, and Architecture

Juniper Networks® Reference Guide: JUNOS™ Routing, Configuration, and Architecture

Thomas M. Thomas II, Doris Pavlichek, Lawrence H. Dwyer III, Rajah Chowbay, Wayne W. Downing III, James Sonderegger

Publisher Resources

ISBN: 9780596805449Errata Page