Failure Recovery Scenario without VPLS STP Redundancy

If VPLS STP (Spanning Tree Protocol) redundancy is not configured on the network shown in the following figure and the S2-R1 link fails, S1 unblocks S1-R1 and S2 flushes its FDB (forwarding database) on the S2-R1 port.

The VPLS core nodes C3 and C4 are unaware of this change and continue to forward any traffic destined for R1 to C2. C2 continues to forward traffic towards S2. This results in data loss because S2 is not able to reach R1 over the customer network.

This data loss continues until one of the following events occurs:

The FDB entry for R1 ages out in the VPLS core nodes
R1 sends traffic into the VPLS core allowing its MAC address to be relearned by the VPLS core nodes

Depending on the type of data traffic from R1, the latter scenario might not occur quickly.

Published March 2020prev | next

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