SR-MPLS Microloop Avoidance

Anti-Micro-Loop Switchover

In Figure 2-77, if Device B fails, traffic is switched to a TI-LFA FRR backup path. After Device A completes route convergence, traffic is switched from the TI-LFA FRR backup path to a converged path. If Devices D and F do not complete route convergence, they transmit traffic over the path established before convergence is performed. As a result, a loop emerges between Devices A and F and is broken after route convergence finishes on Devices D and F.

To prevent the loop-induced problem, the implementation is modified. After Device B fails, traffic is switched to the TI-LFA backup path. Device A delays convergence. After Devices F and D finish path convergence, Device A starts path convergence. After path convergence is complete, traffic is switched from the TI-LFA backup path to the converged path.

Figure 2-77 Anti-micro-loop switchover

Configure the anti-micro-loop switchover function on the source node.

Anti-Micro-Loop Switchback

In Figure 2-78:

1. Data is transmitted along the backup path before the link between Device B and Device C recovers.
2. After the link between Device B and Device C recovers, if Device A converges earlier than Device B, Device A forwards traffic to Device B that does not finish convergence. Upon receipt of the traffic, Device B forwards traffic along the original path to Device A, causing a loop.
3. To prevent a micro loop, after a traffic switchback is performed on Device A, configure an explicit path to forward packets. Device A adds E2E path information (for example, a B-to-C adjacency label) to data packets. Upon receipt of the data packets, Device B forwards packets to Device A, C based on the carried path information.

Figure 2-78 Anti-micro-loop switchback

After Device B finishes convergence, Device A deletes explicit path information from data packets so that the data packets can be forwarded to Device C using normal SR-MPLS.