S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m
Edge quench congestion control provides feedback to the source about the rate at which frames should
be injected into the network (frame intervals).
FCC is not supported on the Cisco Fabric Switch for HP c-Class BladeSystem and Cisco Fabric Switch
for IBM BladeCenter.
When a node in the network detects congestion for an output port, it generates an edge quench message.
These frames are identified by the Fibre Channel destination ID (DID) and the source ID. A switch from
other vendors simply forwards these frames.
Any receiving switch in the Cisco MDS 9000 Family handles frames in one of these ways:
The behavior of the flow control mechanism differs based on the Fibre Channel DID:
All switches (including the edge switch) along the congested path process path quench frames. However,
only the edge switch processes edge quench frames.
By default, the FCC protocol is disabled. FCC can only be enabled for the entire switch.
If you enable FCC, be sure to enable it in all switches in the fabric.
Cisco MDS 9000 Family CLI Configuration Guide
Switch 1 sends
regular traffic to
It forwards the frame.
It limits the rate of the frame flow in the congested port.
If the Fibre Channel DID is directly connected to one of the switch ports, the input rate limit is
applied to that port.
If the destination of the edge quench frame is a Cisco domain or the next hop is a Cisco MDS 9000
Family switch, the frame is forwarded.
If neither of these mechanisms is true, then the frame is processed in the port going towards the FC
Switch 2 sends
to Switch 3
Configuring Fabric Congestion Control and QoS
Switch 3 sends
message to Switch 1
to slow down the
OL-16184-01, Cisco MDS SAN-OS Release 3.x