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Cisco Bug: CSCum87459 - Traffic loss for 120 sec when the chassis which has Primary-DSC go down.

Last Modified

Jan 12, 2017

Products (1)

  • Cisco ASR 9000 Series Aggregation Services Routers

Known Affected Releases

4.3.2.BASE

Description (partial)

Symptom:
When the chassis which has Primary-DSC and the STP fwd port go down(power off and so on), packets using spanning-tree are dropped for about 120 seconds.

Perhaps this symptom is the expected behavior to prevent l2 loop under chassis trouble situation.
Need to clarify that this is not bug.
If this is the bug, need to fix it.

Conditions:
We are using MST in our testbed.

 +- - - - - -+     +- - - - - -+
 |   L2SW    |- - -|   L2SW    |
 |Root bridge|     |           |
 +- - - - - -+     +- - - - - -+
        |              |
        |              |
        |              |
       "1"           "2"
        |fwd           |blk
 +- - - - - - - - - - - - - - +
 |      |              |      |
 | +- - - - -+    +- - - - -+ |
 | |  Rack0  |    |  Rack1  | |
 | | Primary |    |Secondary| |
 | +- - - - -+    +- - - - -+ |
 |         A9K nV Edge        |
 +- - - - - - - - - - - - - - +

In above configuration, if Rack0 goes down, port "2" on ASR9K nV doesn't change into "FWD" for about 120seconds.
Therefore, forwarded packets by STP are dropped during that time.

While port "2" remains BLK, we can see following message once a second in result of "sh spanning-tree trace controller".
Dec 18 18:20:31.722 l2protocols/ethernet/stp/ctrl/fast 1/RSP1/CPU0 t1  --------/--: 0638 L2VPN   :- Ignoring batch end call as either module is not initialized or l2vpn is not synced.
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