Linux tip, Fedora tip / howto: setting up iptables

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setting up iptables

These are the steps to go from the Red Hat/Fedora Core default firewall rules to a minimal set of rules, optionally with two extra rules for Azureus.

  • run system-config-securitylevel and enable the firewall. If you'd like to run an ssh server, check "SSH" as a trusted service, for example
  • run iptables -L --line-numbers: this will list your current firewall rules with line numbers in front of them. We are interested in the ones in the RH-Firewall-1-INPUT chain (list)
  • delete rule 3 (the one with ipv6-crypt as the protocol, also known as protocol number 50):
    iptables -D RH-Firewall-1-INPUT 3
    (unless you need it for VPN and the like)
  • delete the rule with protocol ipv6-auth (also known as protocol number 51). Run iptables -L --line-numbers again to see which number the rule has now!
  • delete the rule with as the destination (unless you're running mDNSResponder, a service that makes it easier to join a network)
  • delete the rule with dpt:ipp (unless you're sharing your printer on a network)
  • if you'd like to add rules, for a bittorrent client like Azureus for example, first delete the last rule (the one with reject-with icmp-host-prohibited), then:
    • add these two rules:
      iptables -A RH-Firewall-1-INPUT -p udp --dport 12345 -j ACCEPT
      iptables -A RH-Firewall-1-INPUT -p tcp --dport 12345 -j ACCEPT
    • add the last rejection rule again:
      iptables -A RH-Firewall-1-INPUT -j REJECT
    • in Azureus, in Tools->Options->Connections, set the TCP and UDP listen port to 12345 (or whichever port you used in the above rules)
    • if you're using a router, for example, don't forget to open port 12345 for TCP and UDP on the router's firewall
  • in the file /etc/sysconfig/iptables-config, make sure the following option is set to "yes":
    (this way your firewall rules are saved when you shutdown)
  • important: don't use system-config-securitylevel anymore: it will overwrite the set of rules you've just created!

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