[CentOS] SYD flood dropped on Sendmail (centos 4.x)

Chris Heiner cheiner at networkdesignsinc.net
Thu Nov 20 19:55:34 UTC 2008

What would you like to know about my situation? I have 6 servers running
Centos 4.x and every time I get a SYD flood on port 110 the servers require
a reboot (all of them). Its been going on for a few months.

I have blocked the first few IP's but now its random, every few weeks.

Its only my Centos boxes as I have others that are not affect by it.

Does the help?

Thanks in advance.

-----Original Message-----
From: centos-bounces at centos.org [mailto:centos-bounces at centos.org] On Behalf
Of Kai Schaetzl
Sent: Thursday, November 20, 2008 11:31 AM
To: centos at centos.org
Subject: Re: [CentOS] SYD flood dropped on Sendmail (centos 4.x)

Chris Heiner wrote on Thu, 20 Nov 2008 08:48:50 -0800:

> My firewall seems to block an attack my Centos / Sendmail boxes on port

port 110 is your POP server, probably dovecot.

> These servers require a reboot after each attack.

Because of what?

> My firewall says it's
> blocked?

I don't see this statement in your logs. How/where does it say this?

> Do I need to patch something on sendmail? Or is my firewall not
> doing its job (Sonicwall)? This is not the first time this has happened.

SYN floods are not unusual, even if it is not an attack. 
What or if you want to do something depends on your situation.


Kai Schätzl, Berlin, Germany
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