>-----Message d'origine-----
>De : xmail-boun...@xmailserver.org
>[mailto:xmail-boun...@xmailserver.org]de la part de Davide Libenzi
>Envoye : mercredi 3 novembre 2010 03:46
>A : XMail Users Mailing List
>Objet : Re: [xmail] problem with mx ip selection on retries
>
>
>On Tue, 2 Nov 2010, fcxm...@aquinet.net wrote:
>
>>
>> Hello Davide
>>
>> I found an problem in xmail when re-trying to connect to mx
>with multiple
>> ips
>>
>> Here is a sample :
>> Assuming domain XX.com have this dns setup
>>
>> xx.com mx 10 mx10.xx.com
>> xx.com mx 20 mx20.xx.com
>>
>> mx10.xx.com A 10.10.10.1
>> mx10.xx.com A 10.10.10.2
>> mx10.xx.com A 10.10.10.3
>>
>> mx20.xx.com A 20.20.20.1
>> mx20.xx.com A 20.20.20.2
>>
>> supposing xmail have now to send a mail @xx.com
>> on first try it use mx10.xx.com at 10.10.10.1 : now the tcp
>connection don't
>> work
>> then os same first try xmail use mx20 at 20.20.20.2 :
>suppose tcp connection
>> don't work too !
>>
>> What i see in a trace is that for ALL the others retries for
>this mail,
>> xmail retries ONLY on SAME ips, 10.10.10.1 and 20.20.20.2
>> It never retry on others mx's ips !! And because there was
>no response from
>> these two ips, mail bounced back to sender after all
>possible retries :-/
>> (i checked the others ips, they responded correctly :-/ but
>xmail never
>> tried them ...)
>>
>> I think this is a major bug :(
>
>Does not look like. XMail would cache (in the MX cache) the *names*,
>which are mx10.xx.com and mx20.xx.com (and, for the duration
>of the TTL).
>Then the names are resolved to IP addresses using OS specific library
>calls (getaddrinfo()).
>
So, I don't understand why using nslookup on the xmail server itself
resolving mx10.xx.com i get all the mx10 ips values round robined :
nslookup mx10.xx.com
10.10.10.2 10.10.10.3 10.10.10.1
another immediate nslookup mx10.xx.com
10.10.10.3 10.10.10.1 10.10.10.2
another
10.10.10.1 10.10.10.2 10.10.10.3
Notice that in the real domain case the dns records default ttl was 2 hours,
no ttl specified in the mx records (so default 2 hours) and none in the A
records too (so default 2 hours)
With xmail retry schedule configured with Qt 300 Qi 1 Qr 10 the retry
schedule was :
01 send-time = 0 (00:00:00) next-try = 300 (00:05:00)
02 send-time = 300 (00:05:00) next-try = 600 (00:10:00)
03 send-time = 900 (00:15:00) next-try = 1200 (00:20:00)
04 send-time = 2100 (00:35:00) next-try = 2400 (00:40:00)
05 send-time = 4500 (01:15:00) next-try = 4800 (01:20:00)
06 send-time = 9300 (02:35:00) next-try = 9600 (02:40:00)
07 send-time = 18900 (05:15:00) next-try = 19200 (05:20:00)
08 send-time = 38100 (10:35:00) next-try = 38400 (10:40:00)
09 send-time = 76500 (21:15:00) next-try = 76800 (21:20:00)
10 send-time = 153300 (42:35:00) next-try = 153600 (42:40:00)
So after retry 05 the next retry is more than 2 hours later, so chance to
get same lookups in same order for mx10 and simutanenously the same ip for
mx20 seems minimal or very 'bad' coincidence.
And notice that exact same think occured for all mails for this domain. One
day more than 20 mails was in xmail queue for retries to this domain, and
all was blocked by same mx's not responding 'bad' ip ! very bad 'chance' to
get same ips :/
The dns server is a bind 9 server on same machine, the xmail use it with
smartdnshost entry in server.tab
Trying with no smartdnshost didn't change anythink, nor changing local dns
address to another 'external' dns server with or without smartdnshost entry
in xmail.
In all configurations, nslookups allways returned the mx ips in round robin
manner even if done at less than the dns entry ttl (here 2 hours) so how to
explain xmail 'use' the same IP ?
Do you think OS getaddrinfo (here win32 windows 2000 sp4 patched) return the
same think in same order (sorting them and returning only the first ip) ?
Supposing nslookup and dig don't use getaddrinfo but use direct dns
connections (and i think it is), how to test OS getaddrinfo ?
Any help to find were is the problem will be appreciated :)
Francis
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