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Feature Description - MPLS 01

NE05E and NE08E V300R003C10SPC500

This is NE05E and NE08E V300R003C10SPC500 Feature Description - MPLS

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The non-stop routing (NSR) technology is an innovation based on the non-stop forwarding (NSF) technology whereas is naturally different from NSF. LDP NSR can ensure that neither the control layer nor the forwarding layer is interrupted when the LDP protocol control level of the local node is faulty (caused by the failure of the main control board) without the help of the neighbor node.


Carriers have increasing demands for IP network reliability. Conventional non-stop forwarding (NSF) and graceful restart (GR) techniques cannot prevent traffic interruptions if a neighbor node does not support GR or multiple nodes fail simultaneously during a GR process. Interruptions occur because a GR-enabled node cannot obtain routing information from or establish control plane connections to neighbor nodes during the GR process. As a result, traffic is interrupted temporarily before the GR process is complete.

Related Concepts

  • High availability (HA): supports a backup channel between the AMB and standby main board (SMB).
  • Non-Stop Routing (NSR): a non-stop routing, is a system control plane failure and the existence of standby control plane under the scene of the neighbor control plane is not aware of a technology, not only limited to routing signaling neighbor relationship is not Interruption, including signaling agreements, and other agreements to support business needs.
  • NSF: enables a node to use the GR mechanism to ensure uninterrupted transmission during an AMB/SMB switchover.
  • Active main board (AMB) and standby main board (SMB): implement control plane processes.


LDP NSR implements LDP data synchronization between the AMB and SMB. The AMB backs up the following LDP data to the SMB on an NSR-enabled node:
  • Label switched path (LSP) forwarding entries

  • Key resources, such as labels and cross connection (XC) entries

  • LDP control blocks


The AMB and SMB must be installed on an NSR-enabled node.

The NSR process is as follows:
  1. The AMB backs up LDP data in a batch to the SMB immediately after the SMB starts.

  2. The AMB backs up LDP data in real time to the SMB.

  3. If the AMB fails, the SMB smoothly takes over services because it obtains the same control and forwarding plane data as that on the AMB.


For details about NSR, see "" in Feature Description - Reliability.

Other Usage

An NSR device can function as a GR Helper. The GR Helper communicates with NSR-disabled devices and responds to neighbor nodes' GR requests during an AMB/SMB switchover.

Usage Scenarios

  • NSR is enabled on a node (for example, PE3 shown in Figure 3-14) when the node has multiple links to balance traffic. NSR helps prevent traffic interruptions that result from a single point of failure. Figure 3-14 shows a typical NSR application.
    Figure 3-14 Typical LDP NSR application
  • NSR minimizes the impact of control plane faults and prevents route flapping on heavily loaded networks.


  • NSR ensures the uninterrupted operation of the forwarding plane, and, if the LDP control plane of the local node fails, allows a standby control plane to retain connections between a local node and its neighbor nodes.
  • An LDP node can also use NSR to implement AMB/SMB switchovers on its own.
Updated: 2019-01-14

Document ID: EDOC1100058933

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