How to list all network connections Centos 7 (Connection tracking)

Question

I have a box with Centos 7 installed.

I am trying to configure some iptables rules and playing with the mangle table and markings

For example on my router I am able to see established network connections with the following command in memory mapped fs (proc).

cat /proc/net/nf_conntrack

But in my current centos installation I don't have any of similar files mapped to the proc fs.

Here is the output of grepping kernel modules

[root@testenv crosp]# lsmod | grep nf_conntrack
nf_conntrack_netlink    36864  0 
nf_conntrack          106496  1 nf_conntrack_netlink
nfnetlink              16384  4 nfnetlink_log,ip_set,nf_conntrack_netlink

I have found the ss utility, but didn't found any information how to see packets marks.

How can I get information about established connections and about marked packages ?

Thanks

Solution

Following are some ways to extract established connection information:

1. cat /proc/net/ip_conntrack -> using proc filesystem

2. conntrack -L -> command line interface for netfilter connection tracking. You can yum install it.

3. Another way is to write an iptable rule to LOG messages (use -j LOG) after your marking rule. Since marking rule is non terminating LOG rule will hit and it can be seen using dmesg.

For options 1 & 2 refer this link section "Chapter 3. Requirements" in order to get the conntrack-tools working if they doesn't work.