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Cisco Bug: CSCur31575 - Poor performance on interface after changing the rate-mode then the speed mode

Last Modified

Feb 20, 2018

Products (1)

  • Cisco MDS 9000 Series Multilayer Switches

Known Affected Releases

5.2(2)

Description (partial)

Symptom:
Two types of symptom may occur.

Type 1: a device connected to an MDS shared rate mode interface (usually an F port including trunking F ports to NPV switches) has poor performance. The peer device reports receive errors such as invalid transmission words, CRC's and out of order frames, and upper layer protocols may report timeouts (such as SCSI timeouts).

Type 2: an MDS dedicated rate mode interface (either E or F type port) randomly has close to, but does not reach, 100% throughput. The peer device does not register any errors.

In both cases, no errors are seen on the affected MDS interface.

Conditions:
This issue only applies to interfaces on a DS-X9248-256K9 or DS-X9232-256K9 MDS switching module that  either:

1a) was previously configured as dedicated rate mode and changed to shared rate mode (type 1), or
1b) was previously configured as shared rate mode and changed to dedicated rate mode (type 2)

and then:
2) the interface speed was changed from a fixed speed to 'auto'.

The impact of this issue can vary from intermittent to severe, depending on the instantaneous total transmit bandwidth demand of the port group the interface is a member of. Specifically, it will occur when the link speed of the affected interface is higher than the instantaneously available bandwidth of the interface from the port group.
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