14 Jul
2017
14 Jul
'17
12:52 a.m.
The strange thing is that ping works ok when TCP doesn't connect.
My first suspicion would be a stateful firewall, but I'm sure you
checked that. Could it be a TTL problem? I'm just guessing here.
- Brian
On Thu, Jul 13, 2017 at 07:07:21PM +0200, Rob Janssen wrote:
I'm curious
as to how long you waited when trying port 25. There
is a five-second delay after the connection is established before
it issues the 220 greeting
I noticed that. But on 44.137.40.2 the TCP connection does not even
establish.
I tried from home (44.137.41.97) and from the gw-44-137 (44.137.0.1)
and both were able to connect:
telnet 44.0.0.1 25
Trying 44.0.0.1...
Connected to 44.0.0.1.
Escape character is '^]'.
220 gw.ampr.org ESMTP Sendmail 8.15.2/8.15.2; Thu, 13 Jul 2017 09:20:58 -0700 (PDT)
quit
221 2.0.0 gw.ampr.org closing connection
Connection closed by foreign host.
However, on 44.137.40.2:
telnet 44.0.0.1 25
Trying 44.0.0.1...
(and nothing more. probably an error when I wait a minute or so)
When running tshark on tunl0 I see the SYN+ACK packets from 44.0.0.1 to 44.137.40.2
and when I do an insert of a rule matching source address 44.0.0.1 before all
other firewall rules I see it matching, but still no ACK is going back.
I have no idea what is going on there. Ping works OK.
Rob
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