Anilrgowda

As I was responding to a post about Gigabit Ethernet networking here on Geekzone, I did some testing using a tool called iperf from NLANR or National Laboratory for Applied Network Research. Iperf is simple to use yet feature rich, and is very useful when it comes to figuring out network issues, providing consistent results during testing.

First, I tested with Windows XP SP2 against an instance of iperf listening on a Windows Server 2003 box:

C:\iperf>iperf -c [server] -w64k -t60

------------------------------------------------------------
Client connecting to [server], TCP port 5001
TCP window size: 64.0 KByte
------------------------------------------------------------
[1884] local [client] port 4885 connected with [server] port 5001
[ ID] Interval Transfer Bandwidth
[1884] 0.0-60.0 sec 5.17 GBytes 740 Mbits/sec

That's pretty good for a Gigabit Ethernet network I thought: I'm using an inexpensive Cnet switch, Cat 5 cabling and both machines use the built-in Intel PRO1000 LAN interface, with the server having an older variant than the client.

As I've noticed networking in Windows Vista seems snappier and it's meant to have some performance enhancing improvements built into the TCP/IP stack compared to XP, I ran a few tests on that OS as well:

D:\iperf>iperf -c devbox -w64k -t60 ------------------------------------------------------------
Client connecting to [server], TCP port 5001
TCP window size: 64.0 KByte
------------------------------------------------------------
[304] local [client] port 50455 connected with [server] port 5001
[ ID] Interval Transfer Bandwidth
[304] 0.0-60.0 sec 6.38 GBytes 913 Mbits/sec

Very close to wire speed, and an improvement of 23.4% in Vista compared to XP.

The above is a simple test sending TCP in one direction, using a 64kbyte window. I expected Vista to increase the window to a large value, but without specifying the -w parameter, only an 8kbyte buffer was used - and iperf only managed around 510Mbit/s throughput.