> # Autosensing

> Autosensing speed is enabled on all 4-Gbps and 8-Gbps switching module interfaces by default. This configuration enables the interfaces to operate at speeds of 1 Gbps, 2 Gbps, or 4 Gbps on the 4-Gbps switching modules, and 8 Gbps on the 8-Gbps switching modules. When autosensing is enabled for an interface operating in dedicated rate mode, 4 Gbps of bandwidth is reserved, even if the port negotiates at an operating speed of 1 Gbps or 2 Gbps.

> To avoid wasting unused bandwidth on 48-port and 24-port 4-Gbps and 8-Gbps Fibre Channel switching modules, you can specify that only 2 Gbps of required bandwidth be reserved, not the default of 4 Gbps or 8 Gbps. This feature shares the unused bandwidth within the port group provided that it does not exceed the rate limit configuration for the port. You can also use this feature for shared rate ports that are configured for autosensing.

> Tip When migrating a host that supports up to 2-Gbps traffic (that is, not 4 Gbps with autosensing capabilities) to the 4-Gbps switching modules, use autosensing with a maximum bandwidth of 2 Gbps. When migrating a host that supports up to 4-Gbps traffic (that is, not 8 Gbps with autosensing capabilities) to the 8-Gbps switching modules, use autosensing with a maximum bandwidth of 4 Gbps.

> You can set the frame format to EISL for all frames transmitted by the interface in SD port mode. If you sent the frame encapsulation to EISL, all outgoing frames are transmitted in the EISL frame format, regardless of the SPAN sources. See the Cisco MDS 9000 Family NX-OS System Management Configuration Guide.

> Refer to the Cisco MDS 9000 Family NX-OS Interfaces Configuration Guide to configure frame encapsulation on an interface.

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