Re: OpenBSD's spamd.

On Tue, 19 Dec 2006, Christopher Hilton wrote:

Oliver Fromme wrote:
Dimitry Andric wrote:
> Oliver Fromme wrote:
> > What does stuttering mean? Is it similar to sendmail's
> > "greet_pause" feature?
> > See here:
> http://www.ualberta.ca/~beck/nycbug06/spamd/mgp00014.html

OK, so the answer to my question seems to be "yes". :-)


Actually I'd say it's similar. If you telnet to port 25 on a server that's using sendmail's greet_pause option I'm assuming that you get nothing for 5 seconds. OpenSD's Spamd sends the initial greeting at a rate of one character per second and only accepts data from you at the same rate.

It also sets the window size to something like 1 byte. :)

Someone had mentioned that this would consume many threads/processes, but that is not the case. Bob explained that spamd runs in a select() loop. I don't totally understand that, but to me it sounds like the same methodology that thttpd used, and that sure scaled up nice.

Here's what I think is the latest version of Bob's talk. It's quite good.

http://www.ualberta.ca/~beck/nycbug06/spamd/

There's audio available here:

http://www.nycbsdcon.org/slides

Was the original question "when will the FreeBSD port be updated"?? :)

Charles

Through experimentation Bob Beck determined that many spammers were dropping the connection and forgetting about delivering the mail completely after short and shorter intervals if the connection was rate limited to 1 character / sec. When the spammers got down to 3 seconds he modified spamd to stutter for 10 seconds on any connection. That feature came in on OpenBSD 3.8

-- Chris
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