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Cisco Bug: CSCvv56650 - ISSU on MDS 9250i FCoE VFCs causes switchport to stop sending PFC Pauses leading to frame drops

Last Modified

Sep 05, 2020

Products (1)

  • Cisco MDS 9000 Series Multilayer Switches

Known Affected Releases

8.4(1) 8.4(1a) 8.4(2) 8.4(2a)

Description (partial)

Symptom:
ISSU on MDS 9250i or MDS 9700 with 10G FCoE module DS-X9848-480K9 with FCoE VFC interfaces can 
cause input packet drops on the ethernet interfaces for the VFCs. The MDS switchport "stops sending PFC Pauses to slow 
the rate of incoming traffic. This leads to congestion drops.

i.e. "GD tx frames with pause opcode for VLx" will not be sent any more.
<pre>
`show hardware internal statistics pktflow dropped`
|------------------------------------------------------------------------|
| Device:Clipper MAC              Role:MAC                     Mod: 1    |
|------------------------------------------------------------------------|
Instance:0
Cntr  Name                                          Value              Ports
----- -----                                         -----              -----
    0 GD Rx bad CRC frames, excluding RUNT/JABBER   0000000000000046   3 -
    1 GD Rx bad CRC frames, excluding RUNT/JABBER   0000000000094502   4 -
    2 PL ingress_pl_drop (truncated or crc etc)     0000000000008972   1 -
    3 PL ingress_congestion_drop_nde_vl3            0000000000364516   1 - <<< Port 1
    4 PL ingress_congestion_drop_bytes_nde_vl3      0000000770426128   1 -
    5 PL ingress_rx_err                             0000000000000046   3 -
    6 PL ingress_pl_drop (truncated or crc etc)     0000000000000046   3 -
    7 PL ingress_rx_err                             0000000000094502   4 -
    8 PL ingress_pl_drop (truncated or crc etc)     0000000000115417   4 -
    9 PL ingress_congestion_drop_nde_vl3            0000000000594821   4 - <<< Port 4 congestion drop
   10 PL ingress_congestion_drop_bytes_nde_vl3      0000001253582196   4 -
   11 IB ingress_ib_drop (small cnt)                0000000000008972   1 -
   12 IB ingress_ib_drop (small cnt)                0000000000000046   3 -
   13 IB ingress_ib_drop (small cnt)                0000000000115417   4 -
   14 IB ingress_ib_de_and_pl_drop (small cnt)      0000000000124906   1-4 -

Conditions:
Occurs only on MDS 9250i, MDS 9700 with DS-X9848-480K9, F2E on N7K/N77 modules only.
Occurs after ISSU to NX-OS 8.4(1) or later version of code.
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