About Buffer-To-Buffer Credits - Cisco MDS 9000 Series Configuration Manual

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
Configuring Interface Buffers
Fibre Channel interfaces use buffer credits to ensure all packets are delivered to their destination. This
chapter describes the different buffer credits available on the Cisco MDS Family switches and modules,
and includes the following topics:
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About Buffer-to-Buffer Credits

Buffer-to-buffer credits (BB_credits) are a flow-control mechanism to ensure that Fibre Channel
switches do not run out of buffers, so that switches do not drop frames. BB_credits are negotiated on a
per-hop basis.
The receive BB_credit (fcrxbbcredit) value may be configured for each Fibre Channel interface. In most
cases, you do not need to modify the default configuration.
The receive BB_credit values depend on the module type and the port mode, as follows:
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OL-19445-02, Cisco MDS NX-OS Release 4.2(x)
About Buffer-to-Buffer Credits, page 4-1
Configuring Buffer-to-Buffer Credits, page 4-2
About Performance Buffers, page 4-2
Configuring Performance Buffers, page 4-3
Buffer Pools, page 4-3
BB_Credit Buffers for Switching Modules, page 4-6
BB_Credit Buffers for Fabric Switches, page 4-16
About Extended BB_Credits, page 4-17
Configuring Extended BB_credits, page 4-19
Enabling Buffer-to-Buffer State Change Number, page 4-19
.About Receive Data Field Size, page 4-20
Configuring Receive Data Field Size, page 4-20
Displaying BB_Credit Information, page 4-21
For 16-port switching modules and full rate ports, the default value is 16 for Fx mode and 255 for
E or TE modes. The maximum value is 255 in all modes. This value can be changed as required.
For 32-port switching modules and host-optimized ports, the default value is 12 for Fx, E, and TE
modes. These values cannot be changed.
For Generation 2 and Generation 3 switching modules, see the
C H A P T E R
Cisco MDS 9000 Family NX-OS Interfaces Configuration Guide
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"Buffer Pools" section on page 4-3.
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