> # Extended BB_Credits

> To facilitate BB_credits for long-haul links, the extended BB_credits feature allows you to configure the receive buffers above the maximum value on all Generation 2, Generation 3 and Generation 4 switching modules. When necessary, you can reduce the buffers on one port and assign them to another port, exceeding the default maximum. The minimum extended BB_credits per port is 256 and the maximum is 4095.

> Note Extended BB_credits are not supported on the Cisco MDS 9148 Fabric Switch, Cisco MDS 9134 Fabric Switch, Cisco MDS 9124 Fabric Switch, the Cisco Fabric Switch for HP c-Class BladeSystem, and the Cisco Fabric Switch for IBM BladeCenter.

> In general, you can configure any port in a port group to dedicated rate mode. To do this, you must first release the buffers from the other ports before configuring larger extended BB_credits for a port.

> Note The ENTERPRISE_PKG license is required to use extended BB_credits on Generation 2, Generation 3 and Generation 4 switching modules. Also, extended BB_credits are not supported by ports in shared rate mode.
> All ports on the Generation 2 and Generation 3 switching modules support extended BB_credits. There are no limitations for how many extended BB_credits you can assign to a port (except for the maximum and minimum limits). If necessary, you can take interfaces out of service to make more extended BB_credits available to other ports.

> You can use the extended BB_credits flow control mechanism in addition to BB_credits for long-haul links.

> This section includes the following topics:

> - Extended BB_credits on Generation 1 Switching Modules
> - Extended BB_credits on Generation 2 and Generation 3 Switching Modules

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