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Cisco Bug: CSCuo82450 - Output discards on FCoE interfaces during congestion

Last Modified

Mar 26, 2019

Products (1)

  • Cisco MDS 9000 Series Multilayer Switches

Known Affected Releases

6.2(9)FM(0.53)

Description (partial)

Symptom:
An egress FCoE interface logs output discards during congestion even though pause frames are sent upstream on the ingress interface. Pause frames received on the egress interface do not prevent the output discards.
    
    Affected ingress interfaces can be identified when the 'ENABLED' field is 1 in the output of the following module-level command:
    
      show hardware internal qengine inst <i>inst-num</i> table vq_voq_td 
    
    where <i>inst-num</i> = quotient of ((the port number - 1) / 4. For example, to verify Ethernet1/1 is affected using 'slot 1' and 'inst 0' as arguments to the above command:
    <pre>
      switch# slot 1 show hardware internal qengine inst 0 table vq_voq_td | include "port|ENABLE|^0"
      | Inst 0; port(s) 1-4
      INDEX  QUEUE  PKT TYPE  VL  THRESHOLD  ENABLE
      0      8q     CRD DE    0   14400      1
    </pre>

Conditions:
This issue only applies to interfaces with a 'no drop' CoS, that is, FCoE interfaces. An interface will be affected by this issue only after a supervisor switchover (this includes ISSU/ISSD switchovers) and then the interface flaps for any reason (this includes moving the interface into a port channel). 
    
    For Nexus 7000/7700 switches, the first affected release is NX-OS release 6.2(2).
    For MDS 9500/9700 switches, the first affected release is NX-OS release 6.2(7).
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