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Single-Fiber Transmission Fails After BFD for IP FRR Is Configured on the NE40 and MGW

Publication Date:  2013-09-03 Views:  157 Downloads:  0

Issue Description

NE40 version: NE40&80 V300R002C01B599
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 MGW-1    MGW-2

BFD for IP FRR is configured on NE40-1 (CE1) and NE40-2 (CE2) for implementing the fast switchover of service traffic.
A service traffic switchover is tested by pinging MGW-2 from MGW-1. When BFD is Down between CE1 and MGW-2 when you simulate a single-fiber transmission failure, ping traffic fails to be switched.

Handling Process

When a router searches the FIB table to forward received packets, the router checks the port state table (PST) of the primary interface if IP FRR is enabled for the FIB table. If the primary interface is available according to the PST, the packets are forwarded through the primary interface; if the PST is Down, the packets are forwarded through the backup interface.
Run the display reroute-tp <slot> command to check the Ethernet interface status on the NE40.

Simulate the switchover. When the problem occurs, quickly search the PST. Three available links (horizontal, upstream, and downstream) are displayed on board 4. Therefore, the FRR protection failure is caused by invalid PST entries.
Simulate the switchover and analyze collected logs. BFD detects unavailable links at 23:59:46 and sends a message indicating the PST modification (Discard[214] row is changed from 33 to 34). All boards modify their PSTs (Discard[212] row is changed from 53 to 54). BFD makes the FRR process take effect.
When traffic is switched back to the faulty interface where the fiber is removed, traffic is interrupted.

Root Cause

BFD detects a fault on the primary link and switches traffic to the backup link. Then BFD discovers that the backup link is also faulty.


1. Enable auto-negotiation function on the interfaces (requiring the support of devices on the core network).
2. Replace the single fiber with the dual-core optical fiber.