Routing traffic back and forth through a Mac mini server with 2 network interfaces

Solution 1:

It should be possible to create a bridge with en0 and en2 and enable net.inet.ip.forwarding to get rid of all routing problems. The bridge acts more or less as another switch between en0 and en2.

• Disable Internet Sharing
• remove the gateway in the en2 settings of the Mac mini and change the IP-address to an available one in 192.168.88.0/24 (e.g. 192.168.88.11)
• remove all additional static routes
• Check for bridge interfaces with ifconfig

• On the server create a file bridge:

  sudo mkdir -p /usr/local/bin/ #only if the folder is missing
  sudo nano /usr/local/bin/bridge
  

  with the content

  #!/bin/bash
  
  sysctl -w net.inet.ip.forwarding=1
  ifconfig bridge create
  ifconfig bridge0 addm en0 addm en2 up #use the first available bridge number here and the proper interface device names
  

• enter sudo chmod +x nano /usr/local/bin/bridge

• Create a launch daemon usr.bridge.plist:

  sudo nano /Library/LaunchDaemons/usr.bridge.plist
  

  with the content

  <?xml version="1.0" encoding="UTF-8"?>
  <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
  <plist version="1.0">
  <dict>
      <key>Label</key>
      <string>usr.bridge</string>
      <key>ProgramArguments</key>
      <array>
          <string>/bin/sh</string>
          <string>-c</string>
          <string>/usr/local/bin/bridge</string>
      </array>
      <key>RunAtLoad</key>
      <true/>
      <key>StandardErrorPath</key>
      <string>/tmp/usr.bridge.err</string>
      <key>StandardOutPath</key>
      <string>/tmp/usr.bridge.out</string>
  </dict>
  </plist>
  

• Load the plist

  sudo launchctl load /Library/LaunchDaemons/usr.bridge.plist
  

• Change the IP-addresses of node_1 and node_10 to available ones in 192.168.88.0/24 (e.g. 192.168.88.101 and 192.168.88.110). Change their default gateways to 192.168.88.1 and the DNS server to 192.168.88.10.