[tor-talk] Tor and iptables.

[Jonathan Marquardt]

You always need to allow some input as well in order for the Tor guard node to 
talk to your computer. Stateful Inspection is used for this. Here's a complete 
ruleset to accomplish what you asked for. All output is allowed, but no input, 
except it belongs to some output your computer previously did.

# Stateful inspection for input and output
iptables -A INPUT -j ACCEPT -m state --state RELATED,ESTABLISHED
iptables -A OUTPUT -j ACCEPT -m state --state RELATED,ESTABLISHED

# Allow loopback traffic
iptables -A INPUT -i lo -j ACCEPT

# Reject any other input
iptables -A INPUT -j REJECT

# Accept all output
iptables -A OUTPUT -j ACCEPT

Note that you also want to accout for IPv6 using ip6tables. It depends on your 
network though.