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Can netfilter manage/filter packets generated by raw sockets

+4 votes
Can netfilter manage/filter packets generated by raw sockets
posted Jan 16, 2014 by Tarun Singhal

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1 Answer

+1 vote

No it can not...

answer Jan 16, 2014 by Sanketi Garg
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+2 votes

I’m recently developing a simple program using netfilter and I’m having a tricky problem. My program is mainly to log the src and dst ip address of all the packets. This program is run in the host machine. I have several virtual machines on that host machine.

The problem is, I can not capture the packets generated or destined at the VMs. All the VMs use bridging network to connect.

Can anyone help me?

+1 vote

Is there a way to find out if there any iptables rules set on a machine ?

There are some indirect ways which will not always work; for example, I know that on most hosts, iptables -S will return the following output (when no iptable rules are set)

So you can check whether or not the number of output lines is greater than 3 (as an indication of whether or not iptables rules are set). But there are hosts on which there are more chains then these 3; these chains are set by application/services, even without any iptable rules which are set. And after running iptables -F on these machines, iptables -S will still show more than 3 chains, even that there are no iptables rules set in these chains.

So the question is - is there a way to know whether or not netfilter rules are set on a host, regardless of the number of chains ?

0 votes

Is it possible to bind multiple address families in netfilter queue? I see IPv4 show up in my queue, but not ARP. With error code removed, here is how I'm calling nfq_bind:

netfilterqueue_handle = nfq_open();
netfilterqueue_queue = nfq_create_queue( netfilterqueue_handle, 0,

nfq_bind_pf( netfilterqueue_handle, AF_INET );
nfq_bind_pf( netfilterqueue_handle, NF_ARP );

I'm thinking the more likely possibility is the iptable rules I'm using to send traffic to the queue are too restrictive. Here are the rules I have:

# Generated by iptables-save v1.4.21 on Sat Feb 14 10:40:46 2015
:INPUT ACCEPT [56:4995]
:OUTPUT ACCEPT [56:4496]
# Completed on Sat Feb 14 10:40:46 2015
# Generated by iptables-save v1.4.21 on Sat Feb 14 10:40:46 2015
:INPUT ACCEPT [1017:217421]
:FORWARD DROP [53:2307]
:OUTPUT ACCEPT [934:211104]
:MYRA - [0:0]
-A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j MYRA
-A FORWARD -s -o eth0 -m conntrack --ctstate NEW -j MYRA
-A MYRA -j NFQUEUE --queue-num 0 --queue-bypass
# Completed on Sat Feb 14 10:40:46 2015

Do I have to add another FORWARD line to get ARP to jump to MYRA? What would it look like?

+1 vote

I know that packet traverses through the Net Filter hooks but how to practically realize that, any suggestions...

+1 vote

Is there a way to bypass nat ftp helper for a few connections and allow the rest of the FTP connections to NAT with the FTP helper module ?

The need is to NAT the FTP control and data connections without conntrack-helpers .

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