Cisco N5K-M1600 - Expansion Module - 6 Ports Troubleshooting Manual page 37

Chapter 2 Troubleshooting FCoE Issues
S e n d d o c u m e n t c o m m e n t s t o n e x u s 5 k - d o c f e e d b a c k @ c i s c o . c o m .
Possible Cause
If the Nexus 5000 switch is connected to a CNA along with slow servers that are not able to handle the
traffic from the switch port, then the server sends Xoff pause frames to the switch to slow it down. This
increments the pause counters when using the show interface ethx/x command.
To verify this situation, perform the following:
•
•
•
If the Rx (Active) and pause counter increment (as shown with the show interface ethx/x
priority-flow-control command), this indicates that the issue is due to Xoff frames received from the
server.
Solution
Xoff pause frames from the server pause the Nexus 5000 interface and reduces the throughput from the
switch to the CNA. On the server, investigate the OS/PCI slot to ensure that they are high-speed servers.
Replace the servers that can run 10gb throughput.
Check if switch is sending pause frames or getting paused
FCoE throughput on servers is very low due to pause frames from the switch. It is then necessary to
check if the switch is sending pause frames or if it is getting paused.
Possible Cause
If the egress FC port is congested, the switch sends PFC frames to the servers. The PFC frames are sent
to reduce its FCoE rate and avoid a drop. If the server is slow or congested, the server sends PFC frames
to the switch interface.
To verify this situation, perform the following:
•
•
•
PFC frames are a MAC-level type of packet and cannot be viewed using the SPAN feature. Analyzer
Note
in-line is required to actually see the PFC frames on the wire.
OL-25300-01
If the Rx (Inactive) and pause counter increment over time (as shown with the show interface ethx/x
priority-flow-control command), then this indicates that the issue is due to Xon frames received
from the CNA.
For a few iterations, check using the show interface ethx/x |grep - i pause command and ensure
that the pause frame count is incrementing.
For a few iterations, check using the show interface ethx/x priority-flow-control command and
ensure that the PFC frame count is incrementing.
For a few iterations, use the show queuing interface ethx/x command and check the pause status.
Example:
Per-priority-pause status
For a few iterations, check using the show interface ethx/x |grep - i pause command and ensure
that the pause frame count (Rx/TX) is incrementing.
For a few iterations, check using the show interface ethx/x priority-flow-control command and
ensure that the PFC frame count (RX/TX) is incrementing.
For a few iterations, check using the show queuing interface ethx/x command to check the pause
status.
: Rx (Active), Tx (Inactive)
Cisco Nexus 5000 Series Troubleshooting Guide
PFC
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