> # 12-Port 4-Gbps Switching Module BB_Credit Buffers

> Table 14-8 lists the BB_credit buffer allocation for 12-port 4-Gbps switching modules.

> Table 14-8 12-Port 4-Gbps Switching Module BB_Credit Buffer Allocation
> BB_Credit Buffer Allocation Type | BB_Credit Buffers Per Port
> --- | ---
> Dedicated Rate Mode 4-Gbps Speed
> ISL 1 | Fx Port
> Default BB_credit buffers | 250 | 16
> Maximum BB_credit buffers | 250 | 16
> Default Performance buffers | 145 | 12
> Total number of BB_credit buffers per module | 5488
> Total number of performance buffers per module | 512 (shared)

> 1ISL = E port or TE port.

> The following considerations apply to BB_credit buffers on 12-port 4-Gbps switching modules:

> - BB_credit buffers for ISL connections can be configured from a minimum of 2 buffers to a maximum of 250 buffers.
> - BB_credit buffers for Fx port mode connections can be configured from a minimum of 2 buffers to a maximum of 250 buffers.
> - By default, 512 performance buffers are preallocated and are shared by all the ports. These buffers are configurable and the buffers are assigned to the port based on the availability of the buffers in the shared pool.
> - There are 2488 extra buffers available as extended BB_credit buffers after allocating all the default BB_credit buffers for all the ports in ISL mode (5488 - (250 * 12)).

> Note Extended BB_credits are allocated across all ports on the switch. That is, they are not allocated by port group.

> Note By default, the ports in the 12-port 4-Gbps switching modules come up in 4-Gbps dedicated rate mode but can be configured as 1-Gbps and 2-Gbps dedicated rate mode. Shared mode is not supported.

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