Can't sleep much last night due to the baby's quirky sleep pattern, so been spending the night reading about TCP congestion avoidance algorithms [1] -- and bufferbloat [2].
So, here's a spark of what (I hope) could be a starter for a deep discussion for us sysadmins/netadmins. (Which is why I decided to post in the -Server list). I've been, um, enjoying bandwidth beyond what I should be experiencing, by extensively tuning the TCP buffers (among others, increasing its max-size to, like, um, 16MB) and using a non-default congestion avoidance algo (namely, H-TCP). However, reading the article from Jim Getty about bufferbloat made me re-think my setup. Another factor that made me re-think my setup is the 'strange' characteristics of traffic between my office and our brand-spankin'-new subsidiary office 14 floors below us: SSH is very nice, but any big file transfers (sftp, http, ftp, cifs, *anything* biggish) will run well only for the first 10 seconds or so, before slowing to a crawl (and even managed to make WinSCP complaining of 'no response for 15 seconds'). But the ping's have no dropped packets at all. Oh, and this slowdownishness also affects some app in the sub office which connects to the MS SQL Server @ HQ. I'm in a bit of quandary; my bandwidth may be ill-gotten, but employees (and the Management) enjoy the current performance. But, then again, connection between HQ and Sub is flakey. Reading more on the comments given in [2], I had thought that traffic shaping -- at least between HQ and Sub -- may be the solution. And I might alleviate the interconnection pressure somewhat by changing to a different algo. Unfortunately, howto's and guides re: traffic shaping and TCP cong-algo that I can find using GooBing seems... outdated. So, some questions popped into my head: 1. Is there a quite-recent and near-up-to-date guide to traffic shaping and/or TCP cong-algo? 1a. Any analisis on the pro's/con's of H-TCP vs CUBIC vs Westwood+ vs (insert some exotic-but-available cong-algo here)? 2. Am I experiencing and/or causing and/or contributing bufferbloat? 3. What else could explain the peculiar traffic characteristics between my HQ and my sub-office? 3a. Will egress traffic shaping help? Any thoughts are welcome. This thread is open for discussion. And forgive me if I write somewhat incoherently; I'm yet to finish my first cup of coffee. [1] http://www.google.com/m?client=ms-opera-mini&channel=new&q=linux+tcp+congestion+avoidance+algorithm&spell=1&ei=wxYNTpjZM6eViAKkpfSCAg&ved=0CAQQvwUoAA [2] http://gettys.wordpress.com/2010/12/06/whose-house-is-of-glasse-must-not-throw-stones-at-another/ Rgds, -- -- Pandu E Poluan - IT Optimizer My website: http://pandu.poluan.info/
