```dv dv.paragraph(("https://jimr.fyi/" + dv.currentFilePath.replace(/\.md$/, "").replace(/ /g, "+"))) ``` ## 📦 Tracking Traffic with `iptables` on a Router ### 🎯 Goal Measure how much data internal servers send to (and receive from) the internet, using `iptables` — no extra software required. --- ### 🛠️ How It Works `iptables` is the Linux firewall. Besides filtering, it tracks: - **Packet counts** - **Byte totals** We use it to count traffic **per internal IP**, like so: ```bash iptables -A FORWARD -s 192.168.1.10 -j ACCEPT ``` This tracks **all traffic from 192.168.1.10** going out through the router. To see totals: ```bash iptables -L FORWARD -v -n -x ``` You’ll get output like: ``` pkts bytes target prot opt in out source destination 1000 500000 ACCEPT all -- * * 192.168.1.10 0.0.0.0/0 ``` Repeat for each internal server IP. --- ### 🧱 Router Type | Router Type | Supports iptables? | Realistic Use | |-------------|--------------------|----------------| | OpenWRT/DD-WRT | ✅ Yes | Great fit | | pfSense/OPNsense | ❌ (uses pf, not iptables) | Use traffic shapers instead | | Consumer router | ❌ Usually not | Flash OpenWRT if possible | | Linux box as router | ✅ Yes | Ideal setup | ### 🧹 Resetting Counts If you want to measure in time blocks (hourly, daily, etc): ```bash iptables -Z ``` That resets counters without deleting rules. --- ### 🛑 Stopping or Cleaning Up To remove a rule: ```bash iptables -D FORWARD -s 192.168.1.10 -j ACCEPT ``` To flush all rules (be careful!): ```bash iptables -F ``` --- ### ⚠️ Limitations - Tracks IPs, not domain names - Doesn’t split by protocol or app - Won’t see traffic not routed through this device (e.g., same-subnet) --- ### 🔁 Bonus: Persist Across Reboot Add rules to `/etc/rc.local`, `iptables-save`, or a startup script depending on your system. --- Let me know if you want a crontab-compatible script to log this automatically.