When you configure IPTables through /etc/network/interfaces using the pre-up directive, the firewall rules automatically load during network interface initialization. Unlike some other Linux distributions, Ubuntu doesn't use /etc/init.d/iptables for firewall management.

To temporarily disable all firewall rules without affecting your persistent configuration:

sudo iptables -F
sudo iptables -X
sudo iptables -Z
sudo iptables -P INPUT ACCEPT
sudo iptables -P FORWARD ACCEPT
sudo iptables -P OUTPUT ACCEPT

For sysadmin work requiring temporary access, consider creating a backup first:

sudo iptables-save > ~/iptables.backup
sudo iptables -F
# Perform your administrative tasks
# Restore when done:
sudo iptables-restore < ~/iptables.backup

For frequent needs, create a simple bash script:

#!/bin/bash
case "$1" in
  stop)
    sudo iptables-save > /tmp/iptables.tmp
    sudo iptables -P INPUT ACCEPT
    sudo iptables -P OUTPUT ACCEPT
    sudo iptables -P FORWARD ACCEPT
    sudo iptables -F
    ;;
  start)
    sudo iptables-restore < /tmp/iptables.tmp
    ;;
esac

Remember that any network service restart or interface reload will trigger your pre-up command again. For longer maintenance windows, you might want to:

sudo ifdown eth0 && sudo ifup eth0

after completing your work to ensure proper rule reloading.

When iptables rules are loaded through /etc/network/interfaces using the pre-up directive, they become persistent across reboots. The configuration you've shown:

pre-up iptables-restore /etc/firewall.txt

means your firewall rules are automatically restored every time the network interface comes up. This is why simply stopping a service won't work - Ubuntu doesn't have a traditional /etc/init.d/iptables service like some other distributions.

The most straightforward way to temporarily disable iptables is to flush all rules and set default policies to ACCEPT:

sudo iptables -F
sudo iptables -X
sudo iptables -t nat -F
sudo iptables -t nat -X
sudo iptables -t mangle -F
sudo iptables -t mangle -X
sudo iptables -P INPUT ACCEPT
sudo iptables -P FORWARD ACCEPT
sudo iptables -P OUTPUT ACCEPT

This will effectively disable all firewall filtering while keeping the iptables framework running.

For more controlled temporary disabling during system maintenance:

# Backup current rules
sudo iptables-save > ~/iptables.backup

# Disable firewall temporarily
sudo iptables -F && sudo iptables -X && sudo iptables -P INPUT ACCEPT

# After maintenance, restore rules
sudo iptables-restore < ~/iptables.backup

If you need to prevent the automatic restoration from /etc/firewall.txt during your maintenance window:

# Temporarily comment out the pre-up line
sudo sed -i 's/^pre-up iptables-restore/#pre-up iptables-restore/' /etc/network/interfaces

# Bring interface down and up to apply changes
sudo ifdown eth0 && sudo ifup eth0

# After maintenance, uncomment the line
sudo sed -i 's/^#pre-up iptables-restore/pre-up iptables-restore/' /etc/network/interfaces

For systems with ufw (Uncomplicated Firewall) installed:

# Disable temporarily
sudo ufw disable

# Enable after maintenance
sudo ufw enable

Remember that disabling iptables leaves your system unprotected. Always:

• Perform this only on secured internal networks
• Re-enable firewall immediately after maintenance
• Consider using SSH VPN tunnels instead of complete disable
• Monitor network traffic during the disabled period