Cisco Systems DSC9148D8G48PK9 manual Information About Interface Buffers, Buffer-to-Buffer Credits

C H A P T E R 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.

	Cisco MDS 9000 Family NX-OS Interfaces Configuration Guide
OL-29284-01, Release 6.x		4-1