Cisco N5K-M1600 - Expansion Module - 6 Ports Troubleshooting Manual page 66

PFC
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 .
switch#
PFC
Link pause (flow control) not enabled on back to back Nexus 5000 switch links
When link pause (flow control) is not enabled on back-to-back Nexus 5000 switch links, packets are
dropped while sending traffic on a no-drop class.
Possible Cause
If the peer Nexus 5000 switch supports PFC TLV with DCBX, then configuring flowcontrol send on
and flowcontrol receive on will not enable the link pause. You have to disable the PFC TLV sent by
DCBX on that interface.
Use one of the following commands to verify:
•
•
Solution
Configure the following commands under interface ethx/y to enable link pause instead of PFC on back-
to-back switch links.
•
•
•
Cannot enable "pause no-drop" on more than one ethernet class
Cannot enable pause no-drop on more than one Ethernet class.
CLI commands fail with the following error when trying to enable pause no-drop.
ERROR:
configuration and re-apply"
Possible Cause
Nexus 5000 supports a maximum of three no drop classes (including FCoE). If five Ethernet classes are
created, then there will be insufficient buffers to enable twoof the five Ethernet no-drop classes.
You will get an error if not enough buffers exist to enable the no-drop.
Example:
class type network-qos s4
pause no-drop
ERROR:
configuration and re-apply"
Solution
Cisco Nexus 5000 Series Troubleshooting Guide
4-8
Use the show interface ethx/y flowcontrol command and check to see if the operating state is off.
Use the show interface ethx/y priority-flow-control command and check to see if the operating
state is on.
no priority-flow-control mode on
flowcontrol receive on
flowcontrol send on
Module 1 returned status "Not enough buffer space available. Please change your
Module 1 returned status "Not enough buffer space available. Please change your
Chapter 4 Troubleshooting QoS Issues
OL-25300-01