Asset ID:	1-71-1009240.1
Update Date:	2009-07-27
Keywords:

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Solution Type  Technical Instruction Sure

Solution  1009240.1 :   Ethernet MDI/MDI-X auto-sensing  


PreviouslyPublishedAs
212785

Description
Many newer Ethernet switches and NICs support auto-sensing of MDI/MDI-X.
This eliminates the need for a crossover network cable when connecting one
system directly to another system without a switch, or when connecting a
switch to a switch not using a "up-link" port.

Steps to Follow
When using copper (UTP, RJ45) interfaces, a standard network cable is used
when connecting a system to a switch.
Such a cable uses one-to-one wiring. Historically, a crossover or MDI-X cable would need to be used when directly connecting a system to another system or switch to another switch.

MDI (medium dependent interface)
MDI-X (MDI crossover)
UTP (Unshielded Twisted Pair copper cable standard)
RJ45 ("Western" type ethernet connector)

Some switches have the ability to configure a port as a "up-link" or MDI-X
port for connecting to another switch using a standard network cable. Some
have a dedicated port for this purpose.

Interface cards in system historically needed to use a crossover or MDI-X
cable to link directly to another system.

New generation Ethernet cards and switches use auto-sensing to accomplish
this, making the establishment of these links  more convenient. Namely,
Gigabit Ethernet interfaces have this feature.

Current Sun[TM] devices that support auto-sensing of MDI/MDI-X are:

ce (GigaSwift) and bge Ethernet Interfaces
and
B1600 Switch, NETP ports


IMPORTANT:
MDI/MDI-X cable detection will not work unless auto-negotiation is on or
enabled.

If auto-negotiation is disabled, auto-MDI/MDI-X pin signal configuration
will also be disabled. This means that you will have to use a cross-over
cable to connect two systems back to back. If you are connecting to a switch,
and the switch doesn't have the ability to configure an up-link port
or have a hard wired up-link port, you will also need to use a MDI-X cable.

An alternative is to leave auto-negotiation enabled (this is the default
setting) but reduce the subset of permitted modes to the single mode that
you want to use.

For example, to force an uplink to 1000BASE-T and retain MDI/MDI-X auto-
sensing, have the port set to
negotiate but with "1000full" as the only capability.

See also:
Technical Instruction <Document: 1005843.1> - Sun[TM] GigaSwift Gigabit Ethernet Adapters First Checks
Technical instruction <Document: 1001843.1>- bge Gigabit Ethernet First Checks

Product
Sun Quad GigaSwift Ethernet UTP Adapter
Sun GigaSwift Ethernet PCI Adapter
Sun Fire V480 Server
Sun Fire V440R Server
Sun Fire V440 Server
Sun Fire V240 Server
Sun Fire V210 Server
Sun Fire B1600 Blade System Chassis

Internal Comments
For the internal use of Sun Employee's.

See also TSC Network Product Pages at

http://panacea.central.sun.com/net/ce
http://panacea.central.sun.com/net/bge
http://panacea.central.sun.com/net/ethernet

MDI, MDI-X, crossover, uplink, up-link, up, link, auto, negotiation, back, gigabit, ethernet, utp, rj45, down, cable
Previously Published As
77124

Change History
Date: 2004-07-05
User Name: 25440
Action: Approved
Comment: Minor edits ("Ethernet" throughout instead of randomly "Ethernet" and "ethernet", "auto-negotiation" rather than "auto-negotiation", "autonegotiation" and "autoneg", and so on). Publishing.
Version: 0
Date: 2004-07-05
User Name: 25440
Action: Accepted
Comment:
Version: 0

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