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I am writing a utility which will use Conntrack commands to show the connection states. I am a beginner and I wanted to play with the Conntrack before I could start my work. So, when I tried conntrack -L conntrack, I get the output which says there are no flows. But, I do have a telnet and one ssh connection to the machine, which is seen in netstat as in ESTABLISHED state.

I also did tail -f /proc/net/ip_conntrack but didn't see any output.

Am I missing something?

3 Answers 3

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If /proc/net/ip_conntrack is empty, you may have conntrack modules not loaded. Try

modprobe nf_conntrack
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  • I did lsmod | grep nf_conntrack. It shows that conntrack is loaded already. Do I need to configure firewall or something for this to work? As per my understanding, it is not needed for basic testing. Oct 19, 2011 at 23:29
  • I dont know how but it started to work, thanks!! Oct 19, 2011 at 23:52
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You can use iptables module 'conntrack' to do something, then conntrack -L will have output.

iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
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You'll have to modprobe nf_conntrack and it's ipv4/ipv6 modules.

  • modprobe nf_conntrack
  • modprobe nf_conntrack_ipv4
  • modprobe nf_conntrack_ipv6
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  • It seems there's no nf_conntrack_ipv4 nor nf_conntrack_ipv6 modules in Fedora 31 stock kernel (I have installed conntrack-tools and libnetfilter-conntrack packages). I have exactly the same problem but I just have nf_conntrack and nf_conntrack_netlink loaded. I don't know what can be...My Nftables version (0.9.1) or Kernel (5.5.9) isn't compatible?
    – Osqui
    Mar 22, 2020 at 15:08

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