Home Forums AFP548 Community Projects Autofirewall – Network-aware firewall settings

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    I thought I’d post this here in hopes of someone else finding it useful. I decided that I would like the Macs at our University to behave like our PC Laptops do as far as firewalls go, so I made a launchd item and matching script to accomplish this for me.

    Basically, the script is run every time that /var/run/resolv.conf is modified (network connection change, unplug, etc). The script itself looks at the resolv.conf (if it exists) and greps the domain line to figure out if it is on your network or not. If it is on your network, it will disable the firewall (0). As soon as you unplug the network cable or if you join a network that is not one of yours, it enables the firewall (1).

    The script itself is fairly flexible, it uses a case to specify which actions to take using the domain listed in the resolv.conf, but it could be modified to use IP address and various other things. I hope that someone else might find this useful as well.

    Any input or suggestions are definitely welcome.

    Here is the LaunchAgent I’m using to kick off the script:









    And here is the script itself.


    #Written by Nate Walck and Clint Armstrong
    #Liberty University 2009

    #This Script will automatically enable or disable the firewall depending upon which network it is on.

    #This function turns the firewall on or off, depending upon which state is desired.
    #If the firwall is already in the state desired, the script will leave it in that state.

    function firewall {
    #Reads the current state of the firewall and stores it in variable fw
    fw=$(defaults read /Library/Preferences/com.apple.alf globalstate)

    #This compares the option passed to function firewall to its current state.
    if [ “$1” != “$fw” ]
    #If the option pased is different from current state, it changes it to the passed value.
    defaults write /Library/Preferences/com.apple.alf globalstate -int $1
    #For troubleshooting purposes, you can put in ‘say $1’ to see which state is being set.

    #Determines if resolv.conf exists.
    if test -e /var/run/resolv.conf
    #This stores the domain line of resolv.conf into variable NETWORK.
    NETWORK=$(cat /var/run/resolv.conf | grep domain | awk ‘{print $2}’)

    #This case looks at $NETWORK for specific domains and runs commands accordingly
    case “$NETWORK” in

    #If on VPN, function firewall turns the firewall on.
    firewall 1

    #On any other company domain, function firewall turns firewall off.
    firewall 0

    #On any other domain, function firewall turns firewall on.
    firewall 1


    #If no network connection exists, function firewall turns the firewall on.
    firewall 1


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