When managing Linux firewall configurations, there are times when you need to completely reset iptables to a clean state. The standard flushing commands work for most cases, but there are potential edge cases where rules might persist.

Here's the basic sequence most administrators use:

# Flush all rules in filter table (default)
iptables -F

# Flush NAT table rules
iptables -t nat -F

# Flush MANGLE table rules  
iptables -t mangle -F

# Delete all non-default chains
iptables -X

While the above commands handle most cases, some scenarios require additional attention:

• Built-in chains (INPUT, OUTPUT, FORWARD) retain their default policies
• User-defined chains in less common tables (raw, security)
• Persistent rules loaded by services at boot

For thorough cleaning, consider this enhanced approach:

# Set default policies to ACCEPT (temporary)
iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT  
iptables -P OUTPUT ACCEPT

# Flush all tables
for table in filter nat mangle raw security; do
    iptables -t $table -F
    iptables -t $table -X
done

# Zero all counters
iptables -Z

For systems with persistent iptables services:

# On Debian/Ubuntu
systemctl stop netfilter-persistent
# On RHEL/CentOS  
service iptables stop

# Then apply flush commands

After flushing, verify with:

iptables -L -n -v --line-numbers
iptables -t nat -L -n -v --line-numbers
iptables -t mangle -L -n -v --line-numbers

For production systems, consider this pattern:

# Create new rules in a temporary chain
iptables -N TEMP_RULES
# Add your new rules to TEMP_RULES

# Atomic swap (minimizes downtime)
iptables -F
iptables -X
iptables -E TEMP_RULES FILTER_CHAIN

When managing Linux firewall rules, there are times when you need to start from scratch—whether for testing, debugging, or deploying a new ruleset. While the basic `iptables -F` command flushes rules, it may not cover all scenarios. Let's explore a bulletproof method.

Most administrators begin with these commands:

# Flush all chains
iptables -F
iptables -t nat -F
iptables -t mangle -F

# Delete all user-defined chains
iptables -X

While this covers most cases, some scenarios might leave rules behind:

• Custom tables beyond filter/nat/mangle
• Built-in chains that can't be deleted
• Persistent rules loaded at boot

For a complete reset, consider this enhanced approach:

# Flush all rules in all tables
for table in filter nat mangle raw security; do
    iptables -t $table -F
    iptables -t $table -X
done

# Reset all policies to ACCEPT
for table in filter nat mangle raw security; do
    iptables -t $table -P INPUT ACCEPT
    iptables -t $table -P FORWARD ACCEPT
    iptables -t $table -P OUTPUT ACCEPT
done

# Clear non-default chains
iptables -F
iptables -X

# Zero all counters
iptables -Z

For systems using persistent iptables configurations (like those with `iptables-persistent` or `netfilter-persistent`), you'll need to:

# For Debian/Ubuntu systems
echo "" > /etc/iptables/rules.v4
echo "" > /etc/iptables/rules.v6

# For RHEL/CentOS systems
service iptables save
service iptables stop

After clearing, verify with:

iptables -L -n -v --line-numbers
iptables -t nat -L -n -v --line-numbers
iptables -t mangle -L -n -v --line-numbers

For frequent use, create a reset script:

#!/bin/bash
# Full iptables reset script
set -e

echo "Resetting iptables..."

for table in filter nat mangle raw security; do
    iptables -t $table -F
    iptables -t $table -X
    iptables -t $table -Z
done

for table in filter nat mangle raw security; do
    iptables -t $table -P INPUT ACCEPT
    iptables -t $table -P FORWARD ACCEPT
    iptables -t $table -P OUTPUT ACCEPT
done

echo "Reset complete. Current status:"
iptables -L -n -v

Remember that resetting iptables leaves your system temporarily unprotected. Consider:

• Running these commands from local console
• Scheduling during maintenance windows
• Having a backup ruleset ready to load