Question Ethernet switch cannot send simultaneously

Mar 10, 2022
suppose an ethernet switch having three rj45 ports in which 1 and 2 are configured as inputs and 3 as output. Input one sends packets of A1,A2,A3,... and input two sends packets of B1,B2,B3,... The output recieves and sends packets in the form of A1B1,A2B2,A3B3,... Now, suppose I have four rj45 ports and I want to configure them as two inputs and two outputs in which both outputs are exactly the same, that is both have the packets A1B1,A2B2,A3B3,.... Is this possible? I connect all three rj45 connectors into the switch, and I have two machines that send data and one output that is connected to the pc, this case no problem is captured. but when I use the fourth port and mechanically switch between port 3 and 4, the whole network is down ?


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Reactions: gggplaya
This is a strange question modern switches have no real concept of input and output the way you state it.

Almost all switches are what is called non blocking or wire speed. It means every port can send and receive at the maximum rate all at the same time. So a 8 port gigabit switch can be transferring 16gbit of traffic, not that there is a realistic case to actually do that.

There is of course a limit on each port of 1gbit in and 1gbit out, in most cases the end device will hit other limits before you max out the port.


Jul 26, 2012
I want to know how you "configure" a port as input and another one as output. Never seen that option, not even when switches were 10mbps, over $1000/worth their weight in gold. (which meant we just had 10Base-T hubs)
Not really a valid things to be doing. Switches keep mac address table and send the traffic back on the port that they last saw the mac address. This is one of those fundamental things on how a switch functions.
It is critical to a number of function and is done in hardware not software so you can't change it even if you want to.

Now if you get a managed switch that has some very advanced features you might misconfigure stuff say by turning off the mac learning and keying it all the mac addresses on each port yourself. You might also get it to work by misconfiguring port bonding.

But why would you want to do this when every port can send and receive at full port speed simultaneously.