If you still have trouble getting high throughput, the problem may well be in the network. First, use netstat -s to see if there are a lot of TCP retransmissions. TCP retransmits usually indicate network congestion, but can also happen with bad network hardware, or misconfigured networks. You may also see some TCP retransmissions if the sending host is much faster than the receiving host, but TCP flow control should make the number of retransmits relatively low.

pathrate can both be used to get an estimate of the link capacity. If the the capcacity is much lower than expected, this may indicate a network problem or unusually high congestion. Contact your network administrator in this case.

Check the Duplex Mode A common source of LAN trouble with 100BT networks is that the host is set to full duplex, but the ethernet switch is set to half-duplex, or visa versa. Most newer hardware will auto-negotiate this, but with some older hardware, auto-negotiation will sometimes fail, with the result being a working but very slow network (typically only 1-2 Mbps). Its best for both to be in full duplex if possible, but some older 100BT equipment only supports half-duplex. See the duplex checking instructions for some ways to check what your systems are set to.

tcptrace: You can also try using tcpdump to try to see exactly what TCP is doing. tcptrace is a very nice tool for formatting tcpdump output.

Sample Use:

tcpdump -s 100 -w /tmp/tcpdump.out host
hostname
(or on solaris: snoop -s 100 -o /tmp/tcpdump.out dest host hostname )
tcptrace -Sl /tmp/tcpdump.out
xplot /tmp/a2b_tsg.xpl