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How to check whether any netfilter rules are set on a host

+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 ?

posted Nov 29, 2016 by anonymous

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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

My network is like this:

GW+DHCP, eth0: eth1:
HOST1+DHCP, eth0: eth1:

There is a double NAT here at both GW and HOST1. The DHCP from GW is only towards the eth1 network and subnet. The DHCP from HOST1 is only towards eth1.
In GW there is a masquerade rule which works fine and allows all forwarded packets.

I do not want packets from clients in the CLIENT1 side of the network to get access using the nat to the local network resources but that they will have access to the internet using GW. So basically I want to allow all forwarded traffic from the network to be allowed to all networks but not the localnet and the local GW resources.

I am a bit in a conflict in it since the next rules should work or at least should do the trick..:

-A FORWARD -s -i eth1 -p tcp -m state --state ESTABLISHED -j ACCEPT
-A FORWARD -i eth1 -p icmp -j ACCEPT
-A FORWARD -s -i eth1 -p tcp -m multiport --dports 53,443,80,21,22,23,110,25,143,995,993,3128,8080 -j ACCEPT
-A FORWARD ! -i eth1 -m state --state NEW -j DROP
-A FORWARD -o eth1 -j ACCEPT

Before I press the "save" button I would like for someone else to take a small look at it.

+1 vote

How do I add a multiport rule

 nft add rule ip filter output tcp dports 99,200 ip daddr
 counter meta oif eth0 fails.

I see that the range works,

 nft add rule ip filter output tcp dport 99-105 ip daddr
 counter meta oif eth0
+5 votes

I want to forward all http traffic coming in from a perticular IP at local port 8080, to 2 particular IP Addresses (port 80). Is it enough to prepend the following in my IPtable

-A PREROUTING -s xx.xx.xx.xx/24 -p tcp --dport 8080 -j DNAT --to-destination
-A PREROUTING -s xx.xx.xx.xx/24 -p tcp --dport 8080 -j DNAT --to-destination yyy.yyy.yyy.yyy:80