I'm trying to maximize my LAN transfer speed. LAN cards and switch are all gigabit on a CAT 6 cable. Modes are set correctly to 1000 full duplex.

CentOS server

Testing with ftp from both windows and fedora, I'm only having the speed around 11MB/s. On windows I notice that the first few seconds of file transfer I'm actually getting around 25MB/s before it drops to 11MB/s

Can anyone please recommend me what my next step should be to increase this performance?

Are there any utilities I can use to test the file transfer speed without taking hard drive speed into consideration?

The only thing I know is the MTU which I will have to wait until the office hour is over before I can play with it. If there are anything else I should be aware of, please please let me know.

Thank you!


Ipref is the easiest way I know to test network speeds.


If you're using FTP, increase your send and receive buffers.

I wouldn't recommend hard-coding 1000/full; gigabit ethernet is recommended to use autodetect as there is more to the negotiation than simple speed duplex discovery. I'm not so sure that would have anything to do with performance, but it is best practice. I've never had issues with autodetect in a gigabit environment. We used to hard code all 100/full devices as autodetection was sketchy there, but gigabit always seems to detect properly.

This article does a decent job of explaining what is going on with auto detection:



To maximize transfer speed, augment your mtu up to 9000 (jumbo frames). With the same size of header, your frame will be carrying more data, thus increasing the throughput. However, note that this is not supported by all equipements.

And to test this throughput, iperf is a great tool and has graphical frontends like jperf.

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