MacOS – How to remotely monitor whether a Mac is connected to the Internet

If you set the IP-address where Charles is running as a proxy on your iPad you should be able to catch all traffic going to your iPad.

For HTTPS you need to install the Charles Certificate on your iPad and let Charles decrypt your HTTPS traffic en encrypt it again before sending it to your iPad (man-in-the-middle). In the Charles application it's called SSL-Proxying.

http://www.charlesproxy.com/documentation/proxying/ssl-proxying/

OS X Yosemite doesn’t have support for natd binary or ipfw anymore. Instead pfctl is used.

I assume the following IP-adresses/netmasks:

Router: 192.168.0.1/24
Mac mini gateway: en0: 192.168.0.2/24 gateway 192.168.0.1 en1: 192.168.1.2/24
Internal network: 192.168.1.0/24

1. First you have to enable forwarding on your Mac computer with following commands:

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

2. In order to do NAT you have to create a pfctl rule. Create a file called "nat-rules" with the following content:

   nat on en0 from en1 to any -> (en0)
   

3. Save the file and now start pfctl using the rule from the file we have created earlier:

   sudo pfctl -d #disables pfctl
   sudo pfctl -F all #flushes all pfctl rules
   sudo pfctl -f /Path/to/file/nat-rules -e #starts pfctl and loads the rules from the nat-rules file
   

4. Now configure a static route on your router:

   192.168.1.0/24 (the internal network) -> 192.168.0.2 (Mac mini IP-address of the external interface connected to the router)

5. Enable the DHCP-service on your Mac mini gateway:

   • Name: choose a name
   • Network Interface: en1
   • Starting IP address: 192.168.1.10
   • Ending IP address: 192.168.1.100
   • Subnet Netmask: 255.255.255.0
   • Router: 192.168.1.2
   • DNS: some DNS-server (e.g. 8.8.8.8)

6. Now use pfctl to add rules or get a pfctl-GUI like IceFloor or Murus to configure your firewall. Both apps should also allow you to enable NAT (step 2/3)