Linux iptables Dropping Packets — Firewall Troubleshooting
Warninglinux network
Overview
Troubleshoot iptables dropping packets on Linux. Diagnose and fix firewall rules blocking traffic.
Key Details
- Issue: iptables dropping network packets
- Category: Linux Network/Firewall
- Unexpected packet drops causing connection failures
- May affect incoming, outgoing, or forwarded traffic
Common Causes
- Restrictive default DROP policy
- Missing ACCEPT rule for desired traffic
- Rule order wrong — DROP before ACCEPT
- Docker or container rules interfering
Steps
- 1List rules: sudo iptables -L -n -v
- 2Check for drops: sudo iptables -L -n -v | grep DROP
- 3Add accept rule: sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT
- 4Log drops for debugging: sudo iptables -A INPUT -j LOG --log-prefix "IPT-DROP: "
- 5Save rules: sudo iptables-save > /etc/iptables/rules.v4
Tags
linuxlinux-networklinux iptables droppedubuntuterminal
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Frequently Asked Questions
sudo iptables -P INPUT ACCEPT && sudo iptables -F (flushes all rules)