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CHAPTER
4-1
Cisco MDS 9000 Family NX-OS Interfaces Configuration Guide
OL-29284-01, Release 6.x
4
Configuring Interface Buffers
• Information About Interface Buffers, page 4-1
• Configuring Interface Buffers, page 4-21
• Verifying BB_Credit Configuration, page 4-25
Information About Interface Buffers
Fibre Channel interfaces use buffer credits to ensure all packets are delivered to their destination.
This section includes the following topics:
• Buffer-to-Buffer Credits, page 4-1
• Performance Buffers, page 4-2
• Buffer Pools, page 4-2
• BB_Credit Buffers for Switching Modules, page 4-5
• BB_Credit Buffers for Fabric Switches, page 4-16
• Extended BB_Credits, page 4-17
• Buffer-to-Buffer Credit Recovery, page 4-20
• Buffer-to-Buffer State Change Number, page 4-20
• Receive Data Field Size, page 4-21
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:
• 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.