Configuring the MDI Type of an Electrical Interface

Context

Two types of twisted pair cables can be used to connect Ethernet devices:

Straight-through cable: connects different types of devices, such as a switch and a PC, or a switch and a router.
Crossover cable: connects the same type of devices, such as two switches, two routers, or two PCs.

Generally, if two interfaces are connected using a twisted pair cable, the transmit and receive pins of one interface are respectively connected to the receive and transmit pins of the other interface so that the link can be Up. Straight-through and crossover cables have different pin assignments. Ethernet interfaces must support negotiation and crossover of receive and transmit pins to adapt to the cables connected to them. The device supports three medium dependent interface (MDI) types: auto, normal, and across.

Generally, when two interfaces at both ends of a link use the auto type, they can communicate regardless of whether a straight-through or crossover cable is used. You need to manually set the MDI type to normal or across only when the device cannot identify the network cable type. When configuring the MDI type on an interface, pay attention to the following points:

When a straight-through cable is used, configure different MDI types for the local and remote interfaces. For example, configure the across type for one interface and normal type for the other interface.
When a crossover cable is used, configure the same MDI type for the local and remote interfaces. For example, configure the across or normal type for both interfaces or auto type for one interface.

Electrical interfaces support the MDI type configuration.

The XGE electrical interfaces on the ES5D21X02T01 card of the S5720-EI, and ES5D21X08T00 card of the S5730-HI, S5731-H, and S5731S-H can only use the auto MDI type.

The MDI type can be configured on an optical interface that has a GE copper module installed. Before installing a GE copper module on a 25GE optical interface, you need to run the port mode ge command to configure the interface to work at the rate of 1 Gbit/s.

Procedure

Run system-view
The system view is displayed.
Run interface interface-type interface-number
The Ethernet interface view is displayed.
Run mdi { across | auto | normal }
The MDI type is set for the Ethernet interface.

By default, an Ethernet interface uses the auto type and automatically identifies the network cable type.

Verifying the Configuration

Run the display interface [ interface-type [ interface-number ] ] command in any view or the display this interface command in the interface view to check the current interface status. Check the Mdi field in the command output.