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[FW-1] FP3, smtp & Unexpected SYN response
- To: [email protected]
- Subject: [FW-1] FP3, smtp & Unexpected SYN response
- From: "Covington, Chris" <[email protected]>
- Date: Sat, 8 Mar 2003 13:26:01 -0500
- Reply-to: Mailing list for discussion of Firewall-1 <[email protected]>
- Sender: Mailing list for discussion of Firewall-1 <[email protected]>
- Thread-index: AcLloCuKgA7oOpURQA2m1vCC4juMgQ==
- Thread-topic: FP3, smtp & Unexpected SYN response
Hi all,
Since switching to SecurePlatform FP3 Edition 2, I've noticed that I get
a few smtp "Unexpected SYN responses" from outside email servers (I
assume) communicating to my mail servers. One in particular seems to be
trying to connect to both of my MX record IPs, but it can't seem to
successfully connect because it keeps retrying periodically (though it
could be some kind of malicious activity, because I do not recognize the
sender, which is from a US government Department of Defense IP block?).
Perhaps FW-1 does not like TLS-encryption & smtp? I am not using the
SMTP security server.
Other instances seem to be from spammers, so fine.
I also see this error messages with other ports when it looks like
obvious attacks, so I assume this FW-1 behavior is helpful in some way.
What exactly is an "Unexpected SYN response"? It sort of reminds me of
the old "unknown established TCP packet" days.
thanks,
Chris
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