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Why cant you just eliminate the need for a switch?

The Manley Man
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Why cant you just eliminate the need for a switch and plug two computers directly with one Ethernet wire?

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4 minutes ago, The Manley Man said:

Why cant you just eliminate the need for a switch and plug two computers directly with one Ethernet wire?

you can

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You can.

 

It's just that back in the day, there was an issue with computers using the reverse pinout compared to switches and routers. So you couldn't with a regular Ethernet cable, you needed a loopback cable. Now, Ethernet ports on computers should be smart enough to figure which pin layout to use. No guarantees if this is universal, so you should get a loopback cable or a coupler that does the job.

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5 minutes ago, The Manley Man said:

Why cant you just eliminate the need for a switch and plug two computers directly with one Ethernet wire?

So packet data goes to the destined system rather than both.

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In the 10 mbps and 100 mbps network card days, in order to connect two computers together you needed to create a crossover cable. Basically, the pairs of wires that transmit data and the pairs of wires that receive data are switched at one connector:

 

crossover.png.5a2ef5af40067fa4e8ae19c21f2207a2.png

 

The above is for 100mbps or lower only, 1gbps and higher cards use all four pairs, so in theory all four pairs of wires must be switched on one connector, not just two.

 

Modern 1 gbps and 10 gbps network cards have circuitry inside them which auto detects how the cable is constructed, if it's pass through (regular, like you find in stores)  or cross over so if you're connecting the other end of the cable into a computer and you're not using a cross-over cable, the network card will automatically correct itself  and will switch the pairs of wires by itself in order to create the crossover cable.

 

So a plain ethernet cable is enough to create connection between computers. All you have to do is make sure each computer has an unique IP (there are IP classes which can be used for this, like 192.168.0.x  where x is from 1 to 254)  and the same subnet mask ( 255.255.255.0 is the classic)

 

PS. And before RJ45 (the jacks you see in the picture), there were 10 mbps network cards with BNC connectors.  With those, you would install a T on each card and you'd have coaxial cable between the cards and a 50 ohm "terminator" at the other end of each "T" :

 

440px-BNC-Technik.jpg.aea64945d75a4c981262f4aa4d61b432.jpg10base5_bnc_connector_aiu_dix.jpg.37115586b45e30e57b8e16210f8c4025.jpg

 

Those days were fun, if one connector was loose, or someone pulled out the terminator from one end, then the whole network would fail... and everyone shared the 10mbps of bandwidth

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You can... There is no need for a switch if you're just going to connect two computers.

 

On 2017-10-18 at 7:30 AM, .spider. said:

The main reason for a switch is the elimination of collision domains.

 

https://en.wikipedia.org/wiki/Collision_domain

If we're going to be pedantic, a switch actually increases the number of collision domains compared to for example a hub (in a sub 1Gbps network). More domains, but smaller.

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