Cisco MDS 9000 Series Configuration Manual page 173

Congestion Detection, Avoidance, and Isolation
These values are only updated periodically at regular intervals. Hence, if the value of the counter that
has changed in a 20-second interval for several times, then only the value that existed at the end of the
20-second interval is recorded. To determine the count that the counter is incremented, the previous value
must be located and subtracted from the current value. In the following example, the
FCP_SW_CNTR_RX_WT_AVG_B2B_ZERO counter is incremented to 7377473 for port fc1/13 on
12/06/17 06:15:20. The previous value was 7377461 at 12/06/17 06:15:00. Hence, in the time interval
between 06:15:00 and 06:15:20, the FCP_SW_CNTR_RX_WT_AVG_B2B_ZERO is incremented by
7377473 – 7377461 = 12.
switch# show logging onboard error-stats | i WT
fc1/13
|12/06/17 06:15:20
fc1/6
|12/06/17 06:15:20
fc1/4
|12/06/17 06:15:20
fc1/13
|12/06/17 06:15:00
fc1/6
|12/06/17 06:15:00
fc1/4
|12/06/17 06:15:00
The show logging onboard error-stats command has several different counters that pertain to SAN
congestion. Most of these counters are module or switch dependent. For information about
tx-credit-not-available or rx-credit-not-available, the following counters are used:
• Interface priority flow control (FCoE only)—Cisco MDS switches track PFC pause frames (transmitted
and received) using the show interface vfc, show interface priority-flow-control, and show logging
onboard error-stats commands.
• Port monitor Tx datarate counter (Fibre Channel only)—Port monitor Tx datarate counter can be configured
to provide information when a port becomes highly utilized in the transmit (Tx) direction. Port monitor
has two thresholds that are called rising threshold and falling threshold. The rising threshold is when the
Tx datarate of a port reaches or exceeds the percentage of the operational-link speed. The falling threshold
is when the Tx datarate of a port reaches or falls below a configured percentage. For each event, an alert
is generated. The time that the port was highly utilized is the time between the rising threshold and falling
threshold alerts. These alerts are recorded in the RMON log in all Cisco MDS NX-OS releases. From
|FCP_SW_CNTR_RX_WT_AVG_B2B_ZERO
|FCP_SW_CNTR_RX_WT_AVG_B2B_ZERO
|FCP_SW_CNTR_TX_WT_AVG_B2B_ZERO
|FCP_SW_CNTR_RX_WT_AVG_B2B_ZERO
|FCP_SW_CNTR_RX_WT_AVG_B2B_ZERO
|FCP_SW_CNTR_TX_WT_AVG_B2B_ZERO
• FCP_SW_CNTR_TX_WT_AVG_B2B_ZERO
• F32_MAC_KLM_CNTR_TX_WT_AVG_B2B_ZERO
• Count of the number of times that an interface was at zero Tx BB_credits for 100 ms. This count
typically indicates congestion at the device that is attached to an interface.
• FCP_SW_CNTR_RX_WT_AVG_B2B_ZERO
• F32_MAC_KLM_CNTR_RX_WT_AVG_B2B_ZERO
• Count of the number of times an interface was at zero Rx BB_credits for 100 ms. This count typically
indicates that the switch is withholding R_RDY primitive to a device attached to an interface of a
switch due to congestion in the path to devices with which it is communicating.
Also, port monitor can generate tx-credit-not-available or rx-credit-not-available alerts (Fibre Channel
only). See the Port Monitor
5, 50i,48S,96S
5,50i,48S,96S
section.
Cisco MDS 9000 Series Interfaces Configuration Guide, Release 8.x
Information About Congestion Detection
|7377473
|337
|7428998
|7377461
|324
|7428994
6
6
155