Re: Connection with SMTP fails
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From: "Hostmaster methusalix.net" <root@methusalix.net>
Hostmaster methusalix.net wrote:
> Hi there,
>
> since the last days I am examining a strange problem while connecting to a
> SMTP server which does not show the banner. At first I thought it is a
> problem with exim from testing but after testing with telnet from several
> different boxes, I noticed that the problem seems to be more deeper. And
> by the way it has nothing to do with DNS oder ident problems. It is only
> this single server to now, which makes trouble.
> Telneting from non-debian boxes works. If trying to connect from a
> debian box, tcpdump output looks like this:
>
> 15:36:18.330348 me.1413 > them.smtp: S 227803692:227803692(0) win 16060 <mss 1460,sackOK,timestamp 69383157 0,nop,wscale 0> (DF) [tos 0x10]
> 15:36:18.380285 them.smtp > me.1413: S 905637469:905637469(0) ack 227803693 win 30660 <mss 1460,sackOK,timestamp 140675877 69383157,nop,wscale 0> [tos 0x60]
> 15:36:18.380326 me.1413 > them.smtp: . ack 1 win 16060 <nop,nop,timestamp 69383162 140675877> (DF) [tos 0x10]
> 15:36:21.795097 them.smtp > me.1413: S 905637469:905637469(0) ack 227803693 win 30660 <mss 1460,sackOK,timestamp 140676220 69383157,nop,wscale 0> [tos 0x60]
> 15:36:28.231108 me.1413 > them.smtp: P 1:7(6) ack 1 win 16060 <nop,nop,timestamp 69384147 140676220> (DF) [tos 0x10]
> 15:36:28.257714 them.smtp > me.1413: . ack 7 win 30660 <nop,nop,timestamp 140676867 69384147> [tos 0x60]
>
> while the last lines repeats after some time.
>
> Comparing the dump with a non-debian box shows, that the second to last line
> is repeated after a short time and then the communication works. I'm not a
> tcp expert, but for me it looks like the other SMTP server is waiting for
> something and repeats its requests. Sending HELO without waiting for the
> banner works by the way and I can send mail by hand via telnet.
>
> My current guess is, that it maybe has something to do with the kernel or
> with its configuration. Until now, there are no ipchains rules and all
> /proc/sys/net/ipv4 settings are the default from potato.
> I'm using 2.2.19 and the other side runs straight-out-the box SuSe 7.0.
> They said, they had already some SMTP problems with other hosts, but they
> fixed it with a newer Sendmail version which is now at 8.10.
>
> Hope someone understands this :o)
>
> jps
--
Crap can work.
Given enough thrust pigs will fly, but it's not necessary a good idea.
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