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Special Forums IP Networking Capture packets (TcpDump) and forwarding them Post 302409942 by ziedf on Saturday 3rd of April 2010 08:12:02 AM
Old 04-03-2010
Question Capture packets (TcpDump) and forwarding them

Hi,

I want to capture a certain type of packets (selected according to the protocol) coming to my PC and then transmit them to another PC. I had the idea to use tcpdump to filter input packets and extract those chosen. Well my questions are:
1- after filtering input packets, those that have not been chosen, are they rejected and lost?
2- now that I have the packets that I want to forward, how can I call the forward operations in Linux Network API ?Smilie

Thank you in advance.
 

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Firewall mark classifier in tc(8)				       Linux					 Firewall mark classifier in tc(8)

NAME
fw - fwmark traffic control filter SYNOPSIS
tc filter ... fw [ classid CLASSID ] [ action ACTION_SPEC ] DESCRIPTION
the fw filter allows to classify packets based on a previously set fwmark by iptables. If it is identical to the filter's handle, the fil- ter matches. iptables allows to mark single packets with the MARK target, or whole connections using CONNMARK. The benefit of using this filter instead of doing the heavy-lifting with tc itself is that on one hand it might be convenient to keep packet filtering and classifi- cation in one place, possibly having to match a packet just once, and on the other users familiar with iptables but not tc will have a less hard time adding QoS to their setups. OPTIONS
classid CLASSID Push matching packets to the class identified by CLASSID. action ACTION_SPEC Apply an action from the generic actions framework on matching packets. EXAMPLES
Take e.g. the following tc filter statement: tc filter add ... handle 6 fw classid 1:1 will match if the packet's fwmark value is 6. This is a sample iptables statement marking packets coming in on eth0: iptables -t mangle -A PREROUTING -i eth0 -j MARK --set-mark 6 SEE ALSO
tc(8), iptables(8), iptables-extensions(8) iproute2 21 Oct 2015 Firewall mark classifier in tc(8)
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