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Juniper MX Series by Harry Reynolds, Douglas Richard Hanks Jr.

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Nonstop Routing and Bridging

NSR and NSB represent the current state of the HA art for Junos. The general concepts of NSR and NSB are very similar, so unless calling out specifics, the terms NSR and NSB are used interchangeably. While any dual RE router can avail itself of NSR, currently only MX platforms support NSB.

Unlike GR, which makes no bones about announcing a control plane restart, with the full expectation of gaining help from its neighbors, NSR is a completely self-contained solution. A successful NSR event has no externally visible symptoms. NSR does not require any protocol extensions, and there is no need for the helper role associated with GR; while the attached neighbors may well be GR capable and therefore able to provide a helper role, the nature of NSR’s self-contained solution means that restart helper services are simply never needed.

In addition, a successful NSR event is not predicated on network stability during a switchover, a fact that greatly improves the chances of hitless switchover, when compared to GR.

NSR is the foundation upon which the In-Service Software Upgrade (ISSU) feature is built. If you plan on using ISSU, you need to have NSR configured also.

Note

On routers that have logical systems configured on them, only the master logical system supports nonstop active routing.

Replication, the Magic That Keeps Protocols Running

The heart and soul of NSR in Junos is protocol replication. The basic concept is to replicate the actual protocol messages between ...

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