Iptables rule on span traffic

Martijn Lievaart m at rtij.nl
Mon Apr 23 07:25:11 CEST 2007

Krishnamoorthy (Siva) Sivakumar wrote:
> -----Original Message-----
> From: netfilter-bounces at lists.netfilter.org [mailto:netfilter-bounces at lists.netfilter.org] On Behalf Of Pascal Hambourg
> Sent: Saturday, April 21, 2007 2:20 PM
> To: netfilter at lists.netfilter.org
> Subject: Re: Iptables rule on span traffic
> Hello,
> Krishnamoorthy (Siva) Sivakumar a écrit :
>> When I run this rule, and try to access a .txt file (with a web
>> browser on a different machine) on the machine running the iptables, I
>> get a log message and the file access is blocked. However, if I try to
>> do the same but for a .txt file residing on a third machine (machine
>> running iptables is able to see the related packets on its interface
>> connected to the span port), I see no log or blocking. 
> As Cédric said, packets which are not destined to the box do not go 
> through the INPUT chains. And since the box is not forwarding traffic, 
> these packets are dropped at the input routing decision stage and do not 
> go through the FORWARD chains either.
> [Siva:] 
> Then is it true that for iptables rules to be effective (fwsnort generated or otherwise), the machine must be "inline". Is there no way to implement iptables rules on "mirrored" traffic. 
> Siva

You could try to turn on forwarding and block all traffic that makes it 
through the snort rules.


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