Hi all,
We use several mimedefang milter servers in parallel. Sendmail makes it easy, and bind helps us with round robin host milter defines. But after one of the milters have been shut down, we found out that DNS round robin with bind sucks. I'll explain why it sucks. Let's say we have three milters, then bind answers us only three possible results: 1) milter. 172800 IN A 10.0.0.1 milter. 172800 IN A 10.0.0.2 milter. 172800 IN A 10.0.0.3 2) milter. 172800 IN A 10.0.0.2 milter. 172800 IN A 10.0.0.3 milter. 172800 IN A 10.0.0.1 3) milter. 172800 IN A 10.0.0.3 milter. 172800 IN A 10.0.0.1 milter. 172800 IN A 10.0.0.2 Do you see whats wrong ? The first entry is always randomized, but the following entries are not, they are sorted ascending. So let's imagine milter 10.0.0.3 has crashed. Then all requests to 157.161.9.21 are beeing redirected to filter 10.0.0.1 since sendmail just takes the next ip following 10.0.0.3. Filter 10.0.0.1 ends then with 2/3 of all connections, 10.0.0.2 with 1/3. This is IMHO unusable and may lead to tempfails and long delay on filtered emails. There are also DNS implementations which behave totally static, like one famous from Microsoft. The order it uses is always the same. Of course, there are also different implementations which behave more random-friendly and would make that patch unneccessary. But the patch is written for bind users in the first place :-) Anyway, I've made a patch to sendmail to fix this problem independent from DNS: http://antispam.imp.ch/patches/patch-sendmail-milterrandom If you find any bugs just tell me :-) Martin Martin Blapp, <[EMAIL PROTECTED]> <[EMAIL PROTECTED]> ------------------------------------------------------------------ ImproWare AG, UNIXSP & ISP, Zurlindenstrasse 29, 4133 Pratteln, CH Phone: +41 61 826 93 00 Fax: +41 61 826 93 01 PGP: <finger -l [EMAIL PROTECTED]> PGP Fingerprint: B434 53FC C87C FE7B 0A18 B84C 8686 EF22 D300 551E ------------------------------------------------------------------ _______________________________________________ NOTE: If there is a disclaimer or other legal boilerplate in the above message, it is NULL AND VOID. You may ignore it. Visit http://www.mimedefang.org and http://www.roaringpenguin.com MIMEDefang mailing list [email protected] http://lists.roaringpenguin.com/mailman/listinfo/mimedefang
