We did some work on this a few years back and got reasonable performance with 35000 tcp connections open at one time. I think our enhancements made their way into the standard linux kernel. It's all in here: N. Provos, C. Lever, "Scalable Network I/O in Linux," May 2000. [FREENIX track, USENIX Technical Conference, San Diego (June 2000).] http://www.citi.umich.edu/techreports/