Mac boots PCs of wireless network

By beerabuser30
Nov 8, 2007
  1. My friend called me with an odd network problem. She works at a law firm with probably 5 desktops. It is setup with a wireless network. A new lawyer joined the firm and she has a Mac notebook. When she gets on the wireless network it kicks everyone else who is wireless off. If she uses and ethernet cord and plugs right in everything works fine. I don't have much else for information but does anyone happen to just have a guess? It doesn't make a lot of sense to me why this would happen.
  2. jobeard

    jobeard TS Ambassador Posts: 9,156   +598

    inspect the wireless config/adaptor for a STATIC IP ADDRESS.
    If found, delete it and set it to use DHCP.

    If a network is running AND a new system comes online with a DUPLICATE IP ADDRESS, the network goes nuts and the side-effects can vary --
    including router shutdowns, killing all network connections, ....
  3. beerabuser30

    beerabuser30 TS Enthusiast Topic Starter Posts: 200

    Good Call didn't even think of that.

    Thank You
  4. jobeard

    jobeard TS Ambassador Posts: 9,156   +598

    For networks with wired and wireless connections, I like to use MAC addresses
    to force DHCP assigned IP addresses; typically in the low end of the subnet,
    eg: --
    these become the KNOWN and trusted systems.

    The wireless connections, typically laptops and therefore LESS TRUSTED,
    will start getting addresses above the last wired assignment, eg and above.

    Now my firewall can allow different rules for the wired vs. wireless :)

    The assumption of course is ALL systems avoid static ip addresses and only rely upon DHCP.
  5. beerabuser30

    beerabuser30 TS Enthusiast Topic Starter Posts: 200

    Isn't there a way to not allow any static ip addresses and have them all forced dhcp?
  6. jobeard

    jobeard TS Ambassador Posts: 9,156   +598

    no, static addressing is set in the NIC properties of each system.

    as your existing wired users were ok until mr wifi arrived, you should
    only have the one system to inspect -- noting for the furture that
    ALL new systems *must* use DHCP :)
  7. Goalie

    Goalie TS Booster Posts: 616

    With enterprise level equipment, you can indeed lock ports which haven't registered with certain services (or weren't pre-registered.) You can also do what is known as lock-and-learn on some middle class equipment, which basically takes a snapshot of connections to a network device, and then doesn't allow deviation from that snapshot. While that prevents static ip users, it also prevents new DHCP clients. Of course the problem here is that middle and enterprise class equipment cost much more than the standard home/small business equipment.

    For a business with 5 users, your best bet to prevent static IP address interference is to use non-standard DHCP pools. Most static IPs from home networks will fall in the 192.168.1.* (or /8, however you prefer it.) Since all of 192.168 is reserved for internal, private use, you could go off and use 192.168.5.* for DHCP. Static IP machines would then only interfere with each other.

    Some smaller routers will allow you to lock down to hardware addresses. If you only allow known NIC addresses, the others wouldn't be routed. Once someone says "I can't get on" you can tell them how to configure things, get their address, then unlock. This is a slight variation on the lock and learn theory, save it's not port specific. At the moment, I can't think of a model that would do that for you, I'm sorry...

    Also keep in mind Mac's can define different network location profiles. I have one for grandparents house that uses DHCP, one for home that uses DHCP but with set DNS servers (my ISP's DNS sucks), and I have one for a friend's house with a static IP. Switching between them isn't hard to do before you connect, and avoids interfering with other potentially intentional configurations.

    Hope that helps.
  8. tipstir

    tipstir TS Ambassador Posts: 2,383   +105

    But there are times you need to use static IP and can't force DHCP where it can always change the IP on you.

    Static IP
    Wireless Access Points
    Wireless Repeater
    Wireless Media Servers
    Wireless Music Media Servers
    File Server
    Print Server
    Web Server

    Even laptops that just don't connect need to be assigned a static IP from DHCP.

    lower numbers 2 and up

    Static IP
    50 or 100 and up 254

    For most homes network or very small business networks.
  9. beerabuser30

    beerabuser30 TS Enthusiast Topic Starter Posts: 200

    I havent touched an Apple computer since elementary school. When going in to change it to DHCP how different is it from using Windows? Or will I recognize most things?
  10. SNGX1275

    SNGX1275 TS Forces Special Posts: 10,689   +395

    Should be pretty straight foward. Apple Menu -> System Preferences -> Network.

    Then after that I'm not entirely sure because I'm not running in Tiger at the moment, which is what I assume you are. But if you aren't, if you are using Leopard it is Airport -> Advanced (in the bottom right of the window) -> TCP/IP tab, then you'll see your DHCP stuff. In Tiger it should be similar...
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