Network traffic

Real time each connection tracking

In freebsd, session table provides real time rx/tx information for each connection. InLinux netfilter router, connections table only includes information on end of connections by default.

from Linux kernel version >= 2.6.18, we can use contract, conntrack provides a full featured command line utility to interact with the connection tracking system

setup conntrack

Set nf_contrack_acct

$ sysctl -w net.netfilter.nf_conntrack_acct=1

Install contrack utility, if you do not have yet

$sudo apt-get install conntrack

List the existing flows

# conntrack -L

Filter out the listing

#conntrack -L -p tcp --dport 22

Update the ct mark

#conntrack -U -p tcp --dport 22 --mark 10

delete entries,

it can also block TCP traffic when

• stateful rule-set that drops traffic in INVALID state
• /proc/sys/net/netfilter/nf_conntrack_tcp_loose to zero.
• # conntrack -D -p tcp --dport 22

Listen to the connection tracking events

#conntrack -E