Buffer-To-Buffer Credits - Cisco Nexus 5500 Series NX-OS Configuration Manual

Information About Fibre Channel Interfaces
Reason Code (long version)
Suspended due to incompatible
speed
Suspended due to incompatible
mode
Suspended due to incompatible
remote switch WWN
Bound physical interface down
STP not forwarding in FCoE
mapped VLAN

Buffer-to-Buffer Credits

Buffer-to-buffer credits (BB_credits) are a flow-control mechanism to ensure that Fibre Channel interfaces
do not drop frames. BB_credits are negotiated on a per-hop basis.
In Cisco Nexus devices, the BB_credit mechanism is used on Fibre Channel interfaces but not on virtual Fibre
Channel interfaces. The receive BB_credit determines the receive buffering capability on the receive side
without having to acknowledge the peer. This is important for links with large bandwidth-delays (long links
with large latency) to be able to sustain line-rate traffic with increased latency.
The receive BB_credit value (fcrxbbcredit) may be configured for each Fibre Channel interface. In most cases,
you do not need to modify the default configuration.
For virtual Fibre Channel interfaces, BB_credits are not used. Virtual Fibre Channel interfaces provide flow
control based on capabilities of the underlying physical Ethernet interface.
The receive BB_credit values depend on the port mode. For physical Fibre Channel interfaces, the default
Note
value is 16 for F mode and E mode interfaces. This value can be changed as required. The maximum value
is 240 .
Cisco Nexus 5500 Series NX-OS SAN Switching Configuration Guide, Release 7.x
14
Description
The interfaces belonging to the
SAN port channel have
incompatible speeds.
The interfaces belonging to the
SAN port channel have
incompatible modes.
An improper connection is
detected. All interfaces in a SAN
port channel must be connected to
the same pair of switches.
The Ethernet interface bound to a
virtual Fibre Channel interface is
not operational.
The Ethernet interface bound to a
virtual Fibre Channel interface is
not in an STP forwarding state for
the VLAN associated with the
virtual Fibre Channel interface
Configuring Fibre Channel Interfaces
Applicable Modes
Only virtual Fibre Channel
interfaces
Only virtual Fibre Channel
interfaces
OL-30895-01