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I'm figuring out the best router for me based on their performance.

When you have a 1 Gbit/s port in full-duplex, does that mean you can send 1 Gbit/s and receive 1 Gbit/s at the same time? Or is it 512 Mbit/s in each direction to sum 1 Gbit/s?

For example, I got a router with 4 Gbit/s ports connected to 4 hosts (all of them with 1 Gbit/s ports as well). How much throughput would I need in order to allow full-duplex connectivity between them?

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This is why and other sites sometimes confusing list 20/200/2000 speeds, examples – Steve-o Sep 15 '11 at 15:08
They should punched for such atrocities. . . – surfasb Sep 15 '11 at 16:59
up vote 16 down vote accepted

A one gigabit port in full duplex means that it can send and receive one gigabit per second in both directions. The back plane of your switch / router / whatever is what controls how many of your ports can be used concurrently.

If your back plane supports 1 gigabit per second you can have computer A copying a file to computer B at 1 gigabit per second but nothing else active (not copying from computer B to computer A or anything at all between computers C or D). If your back plane is 8 gigabits per second all four of your ports can go in both directions full blast all the time. The more capacity in the back plane the more expensive the switch / router becomes.

Please note that this is probably overkill for your network - if you aren't familiar with the duplex and back plane theory you likely will not produce enough load on your network to require it. If you only occasionally want to copy large files pretty much any gigabit switch / router would do the trick.

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Even for small network sysadmins this can be important. With a limited cheap switch doing a large file copy up to a server can kill its download performance. – Zan Lynx Sep 15 '11 at 16:14
Of course, doing a large file copy to a small server's RAID-5 array will also kill its read performance so it may be a wash. – Zan Lynx Sep 15 '11 at 16:14
@Zan Lynx - if this question had been posed on serverfault I would have responded a bit differently. I didn't see a reason to get into the specifics of drive limitations for the scope of the question. :) – Tim Brigham Sep 15 '11 at 16:22
@timbrigham: Exactly. – surfasb Sep 15 '11 at 16:58

Full-duplex Ethernet connections work by making simultaneous use of two physical pairs of twisted cable (which are inside the jacket), wherein one pair is used for receiving packets and one pair is used for sending packets (two pairs per direction for some types of Ethernet), to a directly connected device. This effectively makes the cable itself a collision-free environment and doubles the maximum data capacity that can be supported by the connection.

On Full-Duplex you can send 1gbps and receive 1gbps. In your case you will have 4gbps over 4 ports, if just one of them are using the link it will receive 4gbps of throughput, if all 4 are sharing a high trafic, the 4gbps link will be shared between them and each one will have 1gbps.

You can find more technical information here.

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