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
Extended BB_credits on Generation 1 Switching Modules
The BB_credits feature allows you to configure up to 255 receive buffers on Generation 1 switching
modules. To facilitate BB_credits for long haul links, you can configure up to 3,500 receive BB_credits
on a Fibre Channel port on a Generation 1 switching module.
To use this feature on Generation 1 switching modules, you must meet the following requirements:
OL-16184-01, Cisco MDS SAN-OS Release 3.x
Obtain the ENTERPRISE_PKG license (see
Configure this feature in any port of the full-rate 4-port group in either the Cisco MDS 9216i Switch
or in the MPS-14/2 module (see
Port Group Support for the Extended BB_Credits Feature
The port groups that support extended credit configurations are as follows.
Any one port in ports 1 to 4 (identified as Group 1 in
Any one port in ports 5 to 8 (identified as Group 2 in
Any one port in ports 9 to 12 (identified as Group 3 in
The last two Fibre Channel ports (port 13 and port 14) and the two Gigabit Ethernet ports
do not support the extended BB_credits feature (see
Explicitly enable this feature in the required Cisco MDS switch.
Disable the remaining three ports in the 4-port group if you need to assign more than 2,400
BB_credits to the first port in the port group.
If you assign less than 2,400 extended BB_credits to any one port in a port group, the remaining
three ports in that port group can retain up to 255 BB_credits based on the port mode.
The receive BB_credit value for the remaining three ports depends on the port mode.
The default value is 16 for the Fx mode and 255 for E or TE modes. The maximum value
is 255 in all modes. This value can be changed as required without exceeding the
maximum value of 255 BB_credits.
If you assign more than 2,400 (up to a maximum of 3,500) extended BB_credits to the port in
a port group, you must disable the other three ports.
Be aware that changing the BB_credit value results in the port being disabled and then reenabled.
Disable (explicitly) this feature if you need to nondisruptively downgrade to Cisco SAN-OS Release
1.3 or earlier. When you disable this feature, the existing extended BB_credit configuration is
Chapter 3, "Obtaining and Installing
Cisco MDS 9000 Family CLI Configuration Guide
GIGABIT E THERNET