Re: SMTP Bind Address/Virtual Interfaces

[Carlos G Mendioroz <tron@huapi.ba.ar>]

I really don't know if you can "bind" a socket you are using for
"connecting", i.e., for outgoing tcp connections.
But since you are obviously using linux + iptables, why don't you
just source nat your smtp traffic to whatever interface you want ?

-Carlos

Neal Morgan @ 10/07/2006 04:00 -0300 dixit:
> Greetings all:
> 
> I have experimented some with the suggested scheduler.conf changes to
> specify a bind address for outbound smtp connections.  I find it doesn't
> work as expected when:
> 
> 1) the IP is assigned to a virtual interface
> 2) there are other virtual interfaces on that physical interface in the
> same network
> 3) the IP either has no default gateway assigned in the main table (per
> "ip route show table main"), or has a default gateway but it is not the
> first listed for this network as reported in the main table
> 
> Iptables (output/mangle) logging shows zmailer's first outbound packet
> specifying the wrong IP address (first IP of default route for the
> desired interface).  For example:
> 
> Scheduler.conf has this:
> 
> smtp/*.com
> 	maxchannel=199
> 	maxring=8
> 	command="smtp -s -L [1.2.3.8] -l ${LOGDIR}/smtpout"
> 
> 
> ip route show table main reports:
> default via 1.2.3.1 dev eth4  src 1.2.3.2
> default via 1.2.3.1 dev eth4  src 1.2.3.8
> ...
> 
> Scheduler/SMTP will always use 1.2.3.2 as the bind address even though
> 1.2.3.8 was requested.
> 
> I can supply additional details, but in short it seems zmailer finds the
> first match on the network address and accepts the src address attached
> to it - whether this address is my requested one or not, all scheduler
> smtp connections matching my "-L" use it.  Further, it doesn't seem to
> renegotiate that choice again until after the scheduler has been
> restarted - e.g. a change to the routes doesn't get noticed until the
> next zmailer restart.
> 
> Seems the issue is somewhere in zgetbindaddr or zgetifaddress but I'm a
> little too tired and slow to figure it out now.  Any suggestions on the
> best fix/method to troubleshoot would be appreciated.
> 
> As a side note, smtpserver is perfectly happy binding to my virtual
> interfaces...
> 
> 
> 
> Thanks,
> 
> Neal Morgan
> 
> 
> 
> 
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-- 
Carlos G Mendioroz  <tron@huapi.ba.ar>  LW7 EQI  Argentina
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