Sat, 18 Sep 2010 09:34:55 +0000 nanog-request@nanog.org fuream loqour :

From: "Abel Alejandro" <aalejandro@worldnetpr.com> Subject: Troubleshooting TCP performance tutorial

This past week I have been trying to find the root cause of tcp performance problems of a few clients that are using a third party metro Ethernet for transport. RFC2544 tests (Layer 2) and iperf using UDP give good symmetric performance almost 100% the speed of the circuit. However all kind of TCP tests result in some kind of asymmetrical deficiency,

Walking through the layers, if L2 checks out, & UDP checks out, but TCP does not, you might have a problem "up the stack", @ L4 with TCP. I don't know your test rig / setup, but a few ideas come to mind: - Mismatch in the TCP personality between the hosts - mixing Windows & some UNIX OS flavors, like Sun Solaris 2.8 or others can produce incredible degradation in streaming TCP performance either due to buggy TCP behavior, or one TCP stack supports options the other doesn't, like one side is doing Classic Reno TCP (max 64K) window, doesn't respect or process RFC1323 window-sizing options, but the other side does. It happens UNIX-to-UNIX too, and embedded devices usually don't have robust TCP/IP stacks as well (like hand-held barcode readers, etc.). Any client patch an OS recently? - Someone is doing QoS of some type either expressly or indirectly by effect. Stream / test TCP on multiple ports / sockets to multiple hosts, different OS combinations, or a known good combination - Knoppix Linux boot CD's are great for this kind of thing - send them to a client, pop 'em in, do some testing - once built a test CD for this, fun, gets rid of that long "troubleshoot loop". - MTU / other issue? Did your UDP stream pack full-size payloads? If not, walk up the size of the test packets to the maximum, see what happens. If it breaks somewhere, you have the beginning of an answer, etc. - Not thinking it's the client app since you mentioned you've run a whole set of TCP-based tests. /dmfh -- __| |_ __ / _| |_ 01100100 01101101 / _` | ' \| _| ' \ 01100110 01101000 \__,_|_|_|_|_| |_||_| dmfh(-2)dmfh.cx