Iptables

Managing traffic: iptables and ip6tables

iptables is used to manage IPv4. ip6tables is used to manage IPv6.

Using iptables rules

Ubuntu recommends using ufw to easily manage iptables rules.

1. View current rules: iptables -L
2. Rules are applied in order
   • One a rule ACCEPTs or DROPs a packet, no further rules are applied
3. Three chains: INPUT, FORWARD, OUTPUT

Saving & Restoring iptables rules

1. iptables-save dumps the current iptables to stdout.
2. iptables-restore flushes iptables and restores a iptables-save dump.
3. Procedure
   1. When your iptables is correct, run as root: $ iptables-save > dump.iptables
   2. To flush iptables and reload, run as root: $ iptables-restore < dump.iptables
4. There are additional options to maintain packet/byte counters, skip flushing, or save only one table by name.

Permanently modifying iptables in a debian/ubuntu system

By default, iptables is only stored in memory. Management tools exist for iptables including ufw and the iptables service.

1. iptables initial ruleset comes from /etc/network/interfaces (may be /etc/sysconfig/iptables)

Resources

1. help.ubuntu.com IptablesHowTo
2. nixCraft: How Do I Save Iptables Rules and Settings?
3. askubuntu managing iptables with ip6tables
4. manpages: iptables, iptables-save, iptables-restore