How do I enable IP-forwarding in MacOS X?

Question

What is the correct way to enable IP-forwarding in MacOS X?

More specifically, what is the MacOS X command line quivalent of the following two Linux commands:

echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -A FORWARD -j ACCEPT

Answer 1

You're doing two things there.

1. Enabling IP forwarding. The OS X equivalent might be:

   sysctl -w net.inet.ip.forwarding=1
   

   ...but since I don't know exactly what you're trying to do, this might be technically correct but unhelpful.

2. Adding a largely unnecessary firewall rule. If you haven't changed the default policy for your FORWARD chain (iptables -P FORWARD ...), then this rule does nothing.

   OS X uses the ipfw firewall tools, which are well documented all over the net. Try here, or here

Answer 2

Does Mac OS X IPFW allow port forwarding from local ports to local ports? I have dansguardian 127.0.0.1:8883 and squid 127.0.0.1:3333 running on a mac as my firerules.

I'm trying to do this (on same mac)browser->dansguadian->squid->Internet

so I'm using this rule - fwd 127.0.0.1,8883 tcp from any to any 80

I tried using natd and redirect with little success.