Network Security Hacks

Collect Statistics with Firewall Rules

Make your firewall ruleset do the work for you when you want to collect statistics.

If you want to start collecting statistics on your network traffic but dread setting up SNMP, you don’t have to worry. You can use the firewalling code in your operating system to collect statistics for you.

For instance, if you were using Linux, you could use iptables commands similar to the following to keep track of bandwidth consumed by a particular machine that passes traffic through your firewall:

# iptables -N KRYTEN && iptables -A KRYTEN -j ACCEPT
# iptables -N KRYTEN_IN && iptables -A KRYTEN_IN -j KRYTEN
# iptables -N KRYTEN_OUT && iptables -A KRYTEN_OUT -j KRYTEN
# iptables -A FORWARD -s 192.168.0.60 
            -j KRYTEN_OUT
# iptables -A FORWARD -d 192.168.0.60 -j KRYTEN_IN

This leverages the packet and byte counters associated with each iptables rule to provide input and output bandwidth statistics for traffic forwarded through the firewall. It works by first defining a chain named KRYTEN, which is named after the host that the statistics will be collected on. This chain contains an unconditional accept rule and will be used to quickly add up the total bandwidth that kryten consumes. To itemize the downstream bandwidth kryten is using, another chain is created called KRYTEN_IN. This chain contains only one rule, which is to unconditionally jump to the KRYTEN chain in order for the inbound bandwidth to be added with the outbound bandwidth being consumed. Similarly, ...