I have a rather weird problem. I want to share a VPN connection that has been established by my Mac OS X 10.5 computer with another machine in my network. This is what I did:

1. In the /etc/hostcongig file on the main computer I added the line: IPFORWARDING=-YES-

2. I assigned a fixed IP address to my computer (192.168.178.30), a fixed one to the other machine (192.168.178.60) and my computer's IP address as gateway on the other machine.

3. I connected to my VPN using the internal Mac OS X VPN client (PPTP connection)

4. I run this script:

   #!/bin/sh

   natd -same_ports -use_sockets -unregistered_only -dynamic -interface ppp0 -clamp_mss
   ipfw -f flush
   ipfw add divert natd ip from any to any via ppp0
   ipfw add pass all from any to any
   sysctl -w net.inet.ip.forwarding=1

   Source: Using (and sharing) a VPN connection on your Mac

Now everthing works smootly, however speed is an issue. I get 1,8 MBit/s on my main machine and only 0,3 - 0,6 MBit/s on the other one.

My question: What could possibly be wrong? Do I have to tweak MTU settings, is there any packet inspection ongoing that needs time....? Any help appreciated!