Can two networking device communicate with each other by not following color coding ?

[pankajdav]

Can two networking device communicate with each other by not following proper color codding  ?

[Peter Paluch · Accepted solution]

Hi,

I suppose you mean to say: "Can two networking devices using Ethernet network cards communicate with each other if the cable interconnecting them does not use the correct pinout?"

This strongly depends on how the cable is truly connected. If at least the Rx/Tx pins are connected correctly (even if the colors have not been used properly or the wire pairs have been split) then the Ethernet cards would probably be able to talk 10Mbps; whether they would be able to talk 100Mbps or faster is not certain. If the Rx/Tx pins are not connected correctly then the show's off.

Best regards,
Peter

[Joseph W. Doherty]

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Posting

As Peter has noted, it depends on how incorrectly the pins are wired.

However, with Ethernet, we have MDI and MDI-X interfaces.  Basically, Ethernet requires certain pins to cross-over between the two devices, e.g. one device's transmit should be connected to the other device's receive pin.

This necessary cross-over can be done either by having one device with a MDI interface and the other with a MDI-X interface and using a "straight-thru" cable, or by using a "cross-over" cable with either MDI to MDI or MDI-X to MDI-X.

If you don't have the correct combination of Ethernet ports and connecting cable, the link won't come "up" (i.e. it won't work).

However, many modern switches have auto-MDI ports, which means they will work with the other side having either a MDI or MDI-X port and with either a straight-thru or cross-over cable.

Some older switches, either have two ports that are the same physical port (you only use one, not both), one MDI and one MDI-X, or some switches have some way to configure a port as either MDI or MDI-X.  The dual ports or configuration capable port, is often a switch's "uplink" port.

So, to your original question, actual color coding, itself, means nothing.  What's relevant is what pins are connected to what pins on both ends of a cable, and, if Ethernet, how the port itself is wired.  The color coding is really to just allow us to visually determine what cable strand connects to each pin on both ends of a cable.  (BTW, for straight-thru cables, the two ends color coding should match for the same pins.  For cross-over cables, some of the pins, not all, will be reversed, again, for example, pins 2 and 3. [edit- NB: for pins 2 and 3, I confused with RS232 - for Ethernet, other posts have the correct pins noted for cross-over ])

[casanavep]

the truth is yes, it is most often possible to make devices establish a link with cabling that has been miss-pinned outside of spec.  The issue becomes reliability, ability to hit the full length of the cabling, and ability to establish the highest shared speed capability of both endpoints.  If I making a one meter (3ft) cable between two devices on a table that have little external interference from power or other cabling in immediate proximity, 99% of the time I can make a cable using the wrong color coding and it work, establish a network connection, between the two devices, as long as both ends match (for a DCE to DTE device - clocker to needs clock device, or a device doing MDI to auto-crossover if needed).  Now you do the same color coding that just worked, but was not really a correct pinout and add significant cable length (i.e. longer than 50'), external noise from power cabling or other dense Category cabling, or local noise from PoE (power over Ethernet for things like IP phones) and all the sudden the same pinout has issues, such as: doesn't link up at all, negotiates poorly (i.e. half-duplex or low speed than both ends can actually establish - 10Mbps negotiated even though both ends can do gigabit). Another symptom even when it works is lots of errors on the interface. 

It's like running your car a quart low on oil.  Will it run, yes.  Will you have immediate or eventual problems and will it not perform like it should, absolutely!

Another caveat not known by many, but all seasoned Cisco engineers will have been caught by it at least once in their lifetime, manually setting speed and duplex on most Cisco hardware disabled MDI/MDX.  That means that even is you used an appropriately pinned out straight or cross-pinned (crossover) cable, the port will not come up when one or both ends has been manually set (should never manually set one side as the other will nearly always negotiate half-duplex due to a lack of negotiation response from the remote device). 

[m.agostinelli1]

In ethernet stantard, the transmission uses only 4 of the 8 pins available (the 4 unused pins are needed for power supply in PoE).

1-2 for the tx and 3-6 for the rx on both sides.

If you want a crossover cable you need to invert 1-2 with 3-6 on one side only.

So, for an ethernet connection without PoE, pins 4 5 7 8 are totally ininfluent.

Consider that the standard suggests using a certain sequence to avoid the mutual interference. The current passing through a wire generates an electromagnetic field. The twisting tries to reduce it.

[Peter Paluch]

Hi,

In ethernet stantard, the transmission uses only 4 of the 8 pins available (the 4 unused pins are needed for power supply in PoE).

This was true only for 10Mbps and 100Mbps versions of Ethernet. 1Gbps variant of Ethernet, however, uses all 4 pair (8 wires) simultaneously in both directions. Therefore, for 1Gbps Ethernet to work, all 8 wires must be connected properly and according to the standard.

If you want a crossover cable you need to invert 1-2 with 3-6 on one side only.

Again, this was valid only for 10/100 Mbps versions. With 1Gbps Ethernet, the proper crossover cable is the one that exchanges all four pairs - check out the following page for a nice diagram:

https://www.computercablestore.com/straight-through-crossover-and-rollover-wiring

In fact, 1Gbps Ethernet cards may be unable to operate over a partially-crossed cable. With 1Gbps Ethernet cards, only full crossover cable should be used. It is also noteworthy that most today's 1Gbps Ethernet cards support the auto-cross (Auto-MDIX) function that is capable of "crossing over" a straight-through cable whenever needed, so with these cards, straight-through cables are usually sufficient.

Best regards,
Peter

[pankajdav]

Thanks Mr.Peter..........