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NE40E V800R010C10SPC500 Feature Description - Network Reliability 01

This is NE40E V800R010C10SPC500 Feature Description - Network Reliability
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Understanding the Uninterruptible Service Technology

Understanding the Uninterruptible Service Technology

Related Technologies

Uninterruptible service technologies include:
  • Non-stop forwarding (NSF): This technology ensures data forwarding continuity if a device's control plane fails. NSF is implemented based on graceful restart (GR). This section mainly describes GR implementation. GR ensures service continuity when a device performs an IP/MPLS restart or AMB/SMB switchover. GR requires the collaboration of neighboring devices to back up and restore information such as routing information.

  • Non-stop routing (NSR): This technology enables a device to back up routing and forwarding information from the AMB to the SMB. During an AMB/SMB switchover, NSR enables the device to restore the information, ensuring service continuity. NSR does not require the collaboration of neighboring devices.

GR and NSR have specific requirements on system hardware, software, and protocols. Table 10-1 describes these requirements.
Table 10-1 Requirements on system hardware, software, and protocols

Technology

Requirement on System Hardware

Requirement on System Software

Requirement on System Protocols

GR

  • Main control board redundancy mechanism: The system provides two main control boards: an AMB and an SMB. When a switchover is triggered, the AMB restarts and the SMB becomes the new AMB.

    Figure 10-1 shows a framework model with the main control board redundancy mechanism.

  • Distributed architecture: The forwarding plane is separated from the control plane. Line processing units (LPUs) are used for data forwarding. A main control board runs control-plane software and protocols (such as dynamic routing protocols), learns routes and maintains the routing table, and generates a forwarding information base (FIB). LPUs run forwarding-plane software and forward data based on the FIB generated by the main control board.

    The distributed architecture ensures that LPUs do not restart and that the FIBs on them are not withdrawn during an AMB/SMB switchover.

When the AMB is working properly, it backs up configuration, interface status, and protocol status information to the SMB.

If the AMB fails due to hardware or software errors, the SMB takes over and restarts the control and forwarding planes.

Routing protocols (such as OSPF, IS-IS, and BGP) and other protocols (such as LDP and RSVP) must be extended to support the GR capability.

NSR

NSR has the same requirements on system hardware as GR.

NSR has the same requirements on system software as GR.

NSR has no special requirements on protocols.

Figure 10-1 Framework model with the main control board redundancy mechanism

GR Implementation

When a device performs a protocol restart or AMB/SMB switchover, GR enables the device to instruct its neighboring devices to maintain the adjacencies and routing stability within a specified GR time. After the protocol restart or AMB/SMB switchover is complete, the device restores network topology, routing, and session information with the collaboration of its neighboring devices within a short period of time. During the entire GR process, no route flapping occurs and no forwarding paths change. Therefore, the device can forward service data without interruptions.

Concepts related to GR implementation are as follows:
  • GR restarter: A device that has two main control boards, AMB and SMB. Its routing protocols support the GR capability. When a GR restarter performs an AMB/SMB switchover, it notifies its neighbors of the switchover and instructs them to maintain adjacencies with it.
  • GR helper: A neighbor of a GR restarter. A GR helper must be able to identify GR signaling. When the GR restarter performs an AMB/SMB switchover, the GR helper maintains the adjacency with the GR restarter. After the AMB/SMB switchover is complete, the GR helper assists the GR restarter in restoring network topology information.
    NOTE:

    GR restarters and GR helpers are relative concepts. When the GR capability is enabled on a GR helper, the GR helper can function as a GR restarter.

  • GR session: A GR capability negotiation process between a GR restarter and a GR helper. A GR session includes protocol restart notification and information exchanging during a protocol restart. The GR restarter and GR helper can use a GR session to obtain each other's GR capability.
  • GR time: A period of time taken for a GR restarter and GR helper to establish a GR session. When finding that the GR restarter is Down, the GR helper preserves the topology or routing information sent from the GR restarter within a specified GR time.
Table 10-2 describes GR implementation. Device A functions as a GR restarter, and Device B, Device C, and Device D function as GR helpers.
Table 10-2 GR implementation

Phase

Diagram

Implementation

GR session establishment between the GR restarter and GR helpers

Figure 10-2

The GR restarter and GR helpers establish GR sessions.

AMB/SMB switchover on the GR restarter

Figure 10-3

When the GR restarter performs an AMB/SMB switchover, the GR helpers maintain adjacencies with the GR restarter and retain the routing information related to the GR restarter before the specified GR time expires.

GR session reestablishment between the GR restarter and GR helpers

Figure 10-4

After the GR restarter has performed the AMB/SMB switchover, it sends GR signaling to the GR helpers to reestablish GR sessions.

Recovery of the network topology information on the GR restarter

Figure 10-5

The GR restarter obtains the current topology and routing information from the GR helpers, recalculates routes, updates the routing table, and ages out the old routing information.

Figure 10-2 GR session establishment between the GR restarter and GR helpers

Figure 10-3 AMB/SMB switchover on the GR restarter

Figure 10-4 GR session reestablishment between the GR restarter and GR helpers

Figure 10-5 Recovery of the network topology information on the GR restarter

NSR Implementation

NSR implementation involves the following phases:
  1. Batch backup: NSR is automatically enabled right after the SMB starts. The SMB backs up routing and forwarding information sent by the AMB in batches. Batch backup is performed before real-time backup. NSR cannot perform an AMB/SMB switchover when batch backup is being performed.
  2. Real-time backup: Changes to the control and forwarding planes are backed up from the AMB to the SMB in real time so that NSR will be ready to perform an AMB/SMB switchover and 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 the LPU to send packets to itself instead of the original AMB. The AMB/SMB switchover is rapidly performed so that the routes between the device and its neighboring devices remain reachable.

Figure 10-6 shows NSR networking.

Figure 10-6 NSR networking

Describes NSR implementation.

  • Batch backup


    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 to the SMB in batches.

    • After batch backup is complete, the device enters the redundancy protection state. If the AMB fails, the SMB can become the new AMB and restore data.

    • If the AMB fails before batch backup is complete, the SMB cannot become the new AMB. The fault can be rectified after the device restarts.

  • Real-time backup


    After batch backup is complete, the device enters the real-time backup phase. If the neighbor status or routing information changes on the AMB, the AMB backs up the updated information to the SMB in real time.

  • AMB/SMB switchover


    If the AMB's software or hardware fails, the SMB detects the failure and automatically becomes the new AMB. The new AMB uses the backup data to forward traffic. The LPU sends the information that has been updated during the AMB/SMB switchover to the new AMB. Routes are reachable and traffic forwarding is uninterrupted during the switchover.

Table 10-3 describes the differences between GR and NSR.

Table 10-3 Differences between GR and NSR

Technology

Advantage

Disadvantage

GR

GR has low loads and high performance.

The GR capability must be enabled on all the devices of the entire network and therefore involves complex interworking between devices.

GR cannot be implemented if the control planes of multiple devices fail simultaneously.

After a fault is rectified, GR is slow to restore data and network topology information.

Any network topology or interface status changes may cause GR failures.

NSR

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

NSR ensures proper traffic transmission even if the control planes of multiple nodes fail simultaneously.

After a fault is rectified, NSR rapidly restores data and network topology information.

NSR has heavy loads and low performance.

Software exceptions can cause NSR failures.

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Updated: 2019-01-03

Document ID: EDOC1100055045

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