SYN flood on [2.0.33]

Pawel S. Veselov (
Sun, 1 Mar 1998 20:38:07 +0300 (MSK)

Hello, All !

There was recently a following problem :

Kernel stop responding on 25th port, believing all income connections
are flood. There are a lot "Warning: possible SYN flood from ..." messages.
All of them came from mail relays, e.g.,,
etc, including our local mail relays. I don't believe this was a real attack.

There are also a lot of "validated probe" messages , but I never could
reach 25th port telnetting on it. I got "connected" once, but nothing followed.
In other cases connection failed on timeout.

reboot healed this, of course.

So the question is what made such things to happen, how I can prevent this
or correct the problem without reboot()ing.

Thanx beforehand.


Man is the measure of all things.
		-- Protagoras

    With best of best regards, Pawel S. Veselov (aka Black Angel)
                   Internet e-mail :
    Web page : | ICQ UIN : 5252265

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