lost connections

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lost connections

Sonic
We're getting many lost connections from our new phone systems
voicemail to email service. The actual voicemails and other emails
send OK but we also see constant hits anywhere from every minute to 8
minutes on the mail server from the phone system that are lost
connections. The phone system is an NEC SV9100. Sender and Postfix are
on the same local vlan.
A snippet from the logs:
===============================================
Sep 11 09:41:46 example00 postfix/smtpd[10259]: connect from
sv9100.example.com[10.6.600.11]
Sep 11 09:41:46 example00 postfix/smtpd[10259]: 8AF0A403E24:
client=sv9100.example.com[10.6.600.11]
Sep 11 09:41:46 example00 postfix/cleanup[10262]: 8AF0A403E24: message-id=<>
Sep 11 09:42:03 example00 postfix/smtpd[10259]: lost connection after
DATA (66836 bytes) from sv9100.example.com[10.6.600.11]
Sep 11 09:42:03 example00 postfix/smtpd[10259]: disconnect from
sv9100.example.com[10.6.600.11] helo=1 mail=1 rcpt=1 data=0/1
commands=3/4
Sep 11 09:43:11 example00 postfix/smtpd[10259]: connect from
sv9100.example.com[10.6.600.11]
Sep 11 09:43:11 example00 postfix/smtpd[10259]: 519CA403E24:
client=sv9100.example.com[10.6.600.11]
Sep 11 09:43:11 example00 postfix/cleanup[10262]: 519CA403E24: message-id=<>
Sep 11 09:43:28 example00 postfix/smtpd[10259]: lost connection after
DATA (66621 bytes) from sv9100.example.com[10.6.600.11]
Sep 11 09:43:28 example00 postfix/smtpd[10259]: disconnect from
sv9100.example.com[10.6.600.11] helo=1 mail=1 rcpt=1 data=0/1
commands=3/4
Sep 11 09:50:06 example00 postfix/smtpd[10321]: connect from
sv9100.example.com[10.6.600.11]
Sep 11 09:50:06 example00 postfix/smtpd[10321]: 58CD6403E24:
client=sv9100.example.com[10.6.600.11]
Sep 11 09:50:06 example00 postfix/cleanup[10324]: 58CD6403E24: message-id=<>
Sep 11 09:50:23 example00 postfix/smtpd[10321]: lost connection after
DATA (66767 bytes) from sv9100.example.com[10.6.600.11]
Sep 11 09:50:23 example00 postfix/smtpd[10321]: disconnect from
sv9100.example.com[10.6.600.11] helo=1 mail=1 rcpt=1 data=0/1
commands=3/4
Sep 11 09:50:34 example00 postfix/smtpd[10321]: connect from
sv9100.example.com[10.6.600.11]
Sep 11 09:50:34 example00 postfix/smtpd[10321]: 4E943403E24:
client=sv9100.example.com[10.6.600.11]
Sep 11 09:50:34 example00 postfix/cleanup[10324]: 4E943403E24: message-id=<>
Sep 11 09:50:52 example00 postfix/smtpd[10321]: lost connection after
DATA (66828 bytes) from sv9100.example.com[10.6.600.11]
Sep 11 09:50:52 example00 postfix/smtpd[10321]: disconnect from
sv9100.example.com[10.6.600.11] helo=1 mail=1 rcpt=1 data=0/1
commands=3/4
===============================================
Could this be some configuration in Postfix? Or is it entirely the
senders doing?
Anything I should be looking at?

Thank you,
Chris
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Re: lost connections

Wietse Venema
Sonic:

> We're getting many lost connections from our new phone systems
> voicemail to email service. The actual voicemails and other emails
> send OK but we also see constant hits anywhere from every minute to 8
> minutes on the mail server from the phone system that are lost
> connections. The phone system is an NEC SV9100. Sender and Postfix are
> on the same local vlan.
> A snippet from the logs:
> ===============================================
> Sep 11 09:41:46 example00 postfix/smtpd[10259]: connect from
> sv9100.example.com[10.6.600.11]
> Sep 11 09:41:46 example00 postfix/smtpd[10259]: 8AF0A403E24:
> client=sv9100.example.com[10.6.600.11]
> Sep 11 09:41:46 example00 postfix/cleanup[10262]: 8AF0A403E24: message-id=<>
> Sep 11 09:42:03 example00 postfix/smtpd[10259]: lost connection after
> DATA (66836 bytes) from sv9100.example.com[10.6.600.11]

Also:

> DATA (66621 bytes) from sv9100.example.com[10.6.600.11]
> DATA (66767 bytes) from sv9100.example.com[10.6.600.11]
> DATA (66828 bytes) from sv9100.example.com[10.6.600.11]

Note that:

66836 = 65536 + 1300
66621 = 65536 + 1085
66767 = 65536 + 1231
66828 = 65536 + 1292

All of these are less than 65536 plus 1460 (one ethernet TCP payload).

You need to find someone who can debug TCP-level problems
with a network skiffer. I do not have time for that anymore.

Random suggestions:

- Disable TCP selective ack (sack) in the kernel.

- Disable TCP window scaling (wscale) in the kernel.

Usually, network-level trouble is caused by in-between boxes
(firewalls, traffic shapers) that mis-handle TCP.

        Wietse
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Re: lost connections

Sonic
Thank you!

I think I found the issue - the new phone system was installed
configured on vlan 200, but the smtp settings were copied over from
the old system which was on the default vlan 1 so what was happening
was that the voicemail system was contacting the smtp server via the
vlan 1 address (routed through the gateway) yet the server was also
listening on vlan 200, and although the replies from the server seemed
to go out on the vlan 1 interface there was some issue, either timing
or routing or route confusion. Switching the voicemail system to
contact the smtp server directly on vlan 200 seems to have resolved
the issue (as usual, time will tell).

Chris