| 1 |
Can't sleep much last night due to the baby's quirky sleep pattern, so |
| 2 |
been spending the night reading about TCP congestion avoidance |
| 3 |
algorithms [1] -- and bufferbloat [2]. |
| 4 |
|
| 5 |
So, here's a spark of what (I hope) could be a starter for a deep |
| 6 |
discussion for us sysadmins/netadmins. (Which is why I decided to post |
| 7 |
in the -Server list). |
| 8 |
|
| 9 |
I've been, um, enjoying bandwidth beyond what I should be |
| 10 |
experiencing, by extensively tuning the TCP buffers (among others, |
| 11 |
increasing its max-size to, like, um, 16MB) and using a non-default |
| 12 |
congestion avoidance algo (namely, H-TCP). However, reading the |
| 13 |
article from Jim Getty about bufferbloat made me re-think my setup. |
| 14 |
|
| 15 |
Another factor that made me re-think my setup is the 'strange' |
| 16 |
characteristics of traffic between my office and our |
| 17 |
brand-spankin'-new subsidiary office 14 floors below us: SSH is very |
| 18 |
nice, but any big file transfers (sftp, http, ftp, cifs, *anything* |
| 19 |
biggish) will run well only for the first 10 seconds or so, before |
| 20 |
slowing to a crawl (and even managed to make WinSCP complaining of 'no |
| 21 |
response for 15 seconds'). But the ping's have no dropped packets at |
| 22 |
all. |
| 23 |
|
| 24 |
Oh, and this slowdownishness also affects some app in the sub office |
| 25 |
which connects to the MS SQL Server @ HQ. |
| 26 |
|
| 27 |
I'm in a bit of quandary; my bandwidth may be ill-gotten, but |
| 28 |
employees (and the Management) enjoy the current performance. But, |
| 29 |
then again, connection between HQ and Sub is flakey. |
| 30 |
|
| 31 |
Reading more on the comments given in [2], I had thought that traffic |
| 32 |
shaping -- at least between HQ and Sub -- may be the solution. And I |
| 33 |
might alleviate the interconnection pressure somewhat by changing to a |
| 34 |
different algo. |
| 35 |
|
| 36 |
Unfortunately, howto's and guides re: traffic shaping and TCP |
| 37 |
cong-algo that I can find using GooBing seems... outdated. |
| 38 |
|
| 39 |
So, some questions popped into my head: |
| 40 |
|
| 41 |
1. Is there a quite-recent and near-up-to-date guide to traffic |
| 42 |
shaping and/or TCP cong-algo? |
| 43 |
|
| 44 |
1a. Any analisis on the pro's/con's of H-TCP vs CUBIC vs Westwood+ vs |
| 45 |
(insert some exotic-but-available cong-algo here)? |
| 46 |
|
| 47 |
2. Am I experiencing and/or causing and/or contributing bufferbloat? |
| 48 |
|
| 49 |
3. What else could explain the peculiar traffic characteristics |
| 50 |
between my HQ and my sub-office? |
| 51 |
|
| 52 |
3a. Will egress traffic shaping help? |
| 53 |
|
| 54 |
Any thoughts are welcome. This thread is open for discussion. |
| 55 |
|
| 56 |
And forgive me if I write somewhat incoherently; I'm yet to finish my |
| 57 |
first cup of coffee. |
| 58 |
|
| 59 |
[1] http://www.google.com/m?client=ms-opera-mini&channel=new&q=linux+tcp+congestion+avoidance+algorithm&spell=1&ei=wxYNTpjZM6eViAKkpfSCAg&ved=0CAQQvwUoAA |
| 60 |
|
| 61 |
[2] http://gettys.wordpress.com/2010/12/06/whose-house-is-of-glasse-must-not-throw-stones-at-another/ |
| 62 |
|
| 63 |
Rgds, |
| 64 |
|
| 65 |
|
| 66 |
-- |
| 67 |
-- |
| 68 |
Pandu E Poluan - IT Optimizer |
| 69 |
My website: http://pandu.poluan.info/ |
Archives