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CX11x, CX31x, CX710 (Earlier Than V6.03), and CX91x Series Switch Modules V100R001C10 Configuration Guide 12

The documents describe the configuration of various services supported by the CX11x&CX31x&CX91x series switch modules The description covers configuration examples and function configurations.
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).


Introduction to NSR


Non-stop routing (NSR) is a reliability technique used to prevent switch modules on neighbor nodes from detecting faults in the switch module on a local device when both an active main board (AMB) and a standby main board (SMB) are installed on the local device.


The demand for data, audio, and video services is growing, which impose increasing requirements on IP network reliability. A provider edge (PE) can perform an AMB/SMB switchover if a single point of failure occurs or a maintenance operation (an upgrade, for example) is performed. The PE fails to converge routing information during the AMB/SMB switchover if its neighbor nodes fail simultaneously or these nodes do not support graceful restart (GR). NSR helps the PE converge routing information and ensures uninterrupted forwarding.


NSR prevents route flapping during an AMB/SMB switchover so that services are not affected. NSR satisfies carrier requirements for high IP network reliability.


This section describes principles of NSR.

Related Concepts
  • High availability (HA): supports a backup channel between the AMB and SMB.
  • Non-stop forwarding (NSF): enables uninterrupted traffic forwarding.
  • Non-stop routing (NSR): enables a specific device to use a standby switch module to restore services immediately if an active switch module fails, while the switch modules of neighbor nodes do not detect the fault.
  • Active main board (AMB) and Slave main board (SMB): implement switch module processes.
  • Line interface processing unit (LPU): implements forwarding plane processes.
Advantages and Disadvantages of NSF and NSR

Table 11-4 lists advantages and disadvantages of NSF and NSR.

Table 11-4 Advantages and disadvantages of NSF (GR) and NSR




NSF (Supports the GR protocol.)

NSF loads are light, which allows high system performance.

NSF needs to be enabled on each node of an entire network. The NSF interworking between devices is complex.

NSF fails if the switch modules on many nodes fail simultaneously.

After a fault is removed, NSF is slowly to restore data and network routing information.

Network topology changes may cause NSF failures.


NSR allows a local node to perform an AMB/SMB switchover separately, which means that neighbor nodes do not need to support NSR or detect routing information changes.

NSR ensures proper traffic transmission even if switch modules on many nodes fail simultaneously.

After the fault is removed, NSR rapidly restores data and network routing information.

NSR loads are heavy, which causes poor system performance.

Software exceptions cause NSR failures.

NSR Procedure
The NSR process on the network shown in Figure 11-1 consists of the following phases:
  1. Batch backup: NSR is automatically enabled after the SMB starts. The AMB sends routing and forwarding information in batches to the SMB. A batch backup is performed before a real-time backup. NSR does not perform an AMB/SMB switchover during a batch backup.
  2. Real-time backup: Any updates to the control and forwarding planes can be backed up to the SMB in real time. NSR is ready to perform an AMB/SMB switchover to allow the SMB to take over traffic from the AMB if a fault occurs.
  3. AMB/SMB switchover: If the AMB fails, the SMB detects the failure and becomes the new AMB. The SMB instructs LPUs to send packets to the SMB itself. The AMB/SMB switchover is complete rapidly so that the routes between the local node and its neighbor nodes remain reachable.
Figure 11-1 NSR procedure

Table 11-5 describes the NSR procedure on a specific node.

Table 11-5 NSR procedure




Batch backup

Figure 11-2 Batch backup process

The SMB starts and sends a message about its in-service status to the AMB. After receiving the message, the AMB backs up its data in batches to the SMB.

  • If the AMB fails, the SMB can become a new AMB and restore data.

  • If the AMB fails before the batch backup is complete, the SMB cannot become a new AMB. The node then restarts automatically.

Real-time backup

Figure 11-3 Real-time backup process

If the neighbor status or routing information changes on the AMB, the AMB immediately sends updated information to the SMB.

AMB/SMB switchover

Figure 11-4 AMB/SMB switchover process

If software or hardware of the AMB fails, the SMB detect the failure and automatically becomes the new AMB. The new AMB uses the backed up data to forward traffic. LPUs send the new AMB their information, including which has been updated during the AMB/SMB switchover. Routes are reachable and traffic forwarding is uninterrupted during the switchover.


NSR applies to any device in any networking.



Updated: 2019-08-09

Document ID: EDOC1000041694

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