IPFW configuration between internal computers

Discussion in 'macOS' started by stuthemonkey, Jan 24, 2012.

  1. stuthemonkey macrumors newbie

    Jan 24, 2012
    I have a very unique situation that I am trying to resolve. And I believe it can be resolved with a firewall able to block communications however I am unsure how to setup IPFW to do what I want/need.

    We recently got a software upgrade for a program that now has this program sending out a UDP broadcast across the network. The devices that are expecting to see this work as expected. and all other computers that are on the network ignore this broadcast. However for a reason unknown, a Xerox Phaser printer "hears" this broadcast, thinks its harmful, and shuts itself down. And if this broadcast is running when the printer tries to startup connected to the network it won't boot. It will get to the point where it should connect to the network, "hears" the broadcast, and shuts itself off again.

    Xerox claims it only acts like this when there is something harmful on the network, and agree that since this issue started occuring at the time of the software upgrade this broadcast is the cause. Before we determine this to be the issue, Xerox did replace the nic card in the printer, and also gave us another printer, neither of which worked. Thats when I did some debugging and determined it was this software. If the software is not running, the printer works perfectly fine on the network.

    Now the software communicates to a handful of other computers on the network via 3 ports. What I would like to do is have those three ports blocked from going out to the printer. Both the computer, and printer have static ip addresses, so it shouldn't be a problem with dhcp changing the ips or anything like that.

    So I guess my question is, can IPFW be setup on the computer to block outbound on three specific ports to a specific ip address in the network? i've never used IPFW or configured it so i'm sorry if this is a simple answer, but i've been trying to figure out whats been wrong with this printer for over a month and just now found this software issue. So hopefully this is an easy configuration.

    I've also heard that IPFW doesn't necessarily keep the rules you give it upon restart of the computer, so if thats true, I would also need to know how to set it up that it would keep these rules on and active even after a reboot.

    Thanks for any help anyone can give.
  2. ScoobyMcDoo macrumors 65816

    Nov 26, 2007
    Austin, TX
    Did you ever solve this issue?

    Let me preface by letting you know I am not an expert with IPFW, but I don't think that it is really the right tool for this job. You might consider putting the computer and devices that needs to receive this UDP broadcast on a separate subnet. Then just broadcast to that subnet.

    I think this can also be done with VLANs. In a past company, I brought the entire corporate network to a screeching halt by doing high volume UDP broadcasts. The IT dept at that point my my department on it's own VLAN so we could only harm ourselves.

    Hope this helps.
  3. stuthemonkey thread starter macrumors newbie

    Jan 24, 2012
    Thanks for the reply. I'm not a network expert either, and I had thought about that option. However the computer that sends out the UDP broadcast also needs to talk with multiple of the other computers on this network. And those computers need to be able to print to that printer.

    So I'm not sure how to segregate off this one computer and the ones that need to hear the UDP, but still have that computer able to fully communicate with some of the machines that can't be on a different vlan.

    like I said, not a network expert, so it could be entirely possible. Just beyond my current understanding.

    Thanks again for the input.

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