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BFD Packets Are Discarded on the NE40E Because Some VLAN Packets Are Forwarded Unexpectedly on the Switches

Publication Date:  2013-01-08 Views:  5 Downloads:  0
Issue Description

The networking diagram is as follows:

As shown in the networking diagram, the two NE40Es function as the gateways of the UMG. The sub-interfaces of GE 1/0/1 of either NE40E are configured with BFD and VRRP. BFD sessions are set up between the NE40Es, and the NE40Es are configured to form a VRRP backup group. VRRP Heartbeat packets and BFD packets are forwarded through the S65s.

 

Based on the customer feedback, the BFD session on a sub-interface flaps irregularly and the BFD session flapping events are recorded in the log on the sub-interface. Except this sub-interface, BFD sessions on the other sub-interfaces remain Up. This problem is not found in the same networking at other sites.

Handling Process

1.         The on-site Huawei technical support personnel check the BFD session flapping log "BFD/4/STACHG_TODWN" on the master NE40E and find that DetectDown is displayed in the Diagnostic field. The BFD session goes Down on the master NE40E because the master NE40E fails to receive BFD packets within the specified detection time.

2.         Then they check the BFD session flapping log "BFD/4/STACHG_TODWN" on the backup NE40E and find that NeighborDown is displayed in the Diagnostic field. The backup NE40E has received BFD packets from the master NE40E.

3.         Based on the log information and symptom analysis, the on-site Huawei technical support personnel surmise that the S65s are unidirectional for a specific VLAN. No packet loss occurs on the link from the master NE40E to the backup NE40E or from the backup NE40E to the master NE40E.

4.         The on-site H3C technical support personnel check the statistics on the S65s and find that a large number of unknown VLAN packets on a member interface in the aggregation interface through which the two S65s communicate with each other are discarded. The unidirectional link is suspected to be related to the packet loss.

5.         The problem is resolved after the aggregation interface is replaced.

Root Cause

The BFD packets are discarded on the unidirectional link between the two switches.

 

Solution

The problem is resolved after the aggregation interface is replaced.

Suggestions
Analyzing the four types of BFD session Down in the BFD logs helps make a preliminary location of the problem. Therefore, it is worthwhile to refer to the BFD logs when a BFD session flaps.

END