2 adapters, same subnet, works in XP not in 98

Discussion in 'Wireless Networking' started by Mike MacSween, Apr 23, 2005.

  1. I've got a small network. No DHCP anywhere. NAT on the DSL router. Addresses
    are all manually configured in the 192.168.0.xxx range, subnet mask of
    255.255.255.0

    Just bought a Wireless AP, PCI WiFi card for a desktop, PCMCIA WiFi card for
    the laptop.

    The laptop, running XP Pro, is quite happy having 2 network connections on
    the same subnet (the WiFi and the built in ethernet). Even if they're both
    active.

    The desktop, running Win 98 SE, won't allow it (it as a PCI ethernet card +
    the WiFi adapter). If I disable the TCP->ethernet card then the WiFi
    connection works. But if I don't then the WiFi doesn't work. Can't ping the
    router or anything. Even without the ethernet cable plugged in. What's (a
    bit!) interesting is that while the machine boots, if I get to a command
    window and ping the router, then I might get a couple of replies, as long as
    the WiFi icon has the cross (i.e. 'not working yet') through it. But as soon
    as the WiFi comes alive the connection fails.

    I'm struggling to understand this. My searches on the internet give me the
    answer that you can't have two adapters on the same subnet.

    1. Why not? What is it about TCP/IP addressing that prevents that.

    2. I see a slight difference in the network setup windows for XP and 98. It
    _seems_ to me as though the two hardware devices in the laptop (ethernet
    adapter and WiFi adapter) are bound (?) the same TCP/IP software (?)
    adapter. But I'm guessing. Am I on the right lines? What problems, if any,
    will this cause.

    3. I'll never/hardly ever want to use a wired ethernet connection and a WiFi
    connection at the same time, at least not on the same subnet. But at the
    moment the Win 98 machine doesn't even allow me to leave the ethernet set
    up. So if the WiFi fails, or I just want to move the machine into a
    different room to where I _can_ get a cable at it I'll have to reconfigure
    it.

    The WiFi AP is a D-Link DWL-2000AP+ connected to a NetGear Wired Router/DSL
    modem. All the wired machines are also connected to the router.

    Any help gratefully received.

    Yours, Mike MacSween
     
    Mike MacSween, Apr 23, 2005
    #1
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  2. Mike MacSween

    Kurt Guest

    Pretty straightforward really, a route (route print form the command line)
    to a network is created via a specific interface. Win98 rebuilds the routing
    table any time a change occurs to hardware (or lots of other things).
    Although Window2000/XP allow multiple routes to the same network, it really
    hasn't ever worked very well. The workaround is simple, disable the wired
    adapter when using the WIFI and vice versa. You should disable before
    enabling, which will delete the route, then add it back again via the
    correct adapter. You could also take a look at the routing table and see if
    you have multiple entries for the same network and, if not, add on manually
    and see if W98 will accept it (I'm doubtful since it's a directly connected
    network), and whether or not it knows what to do with it.

    ....kurt
     
    Kurt, Apr 23, 2005
    #2
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  3. No version of Windows can use two network adapters in the same subnet
    at the same time.

    Each network adapter has associated entries in the route table. When
    route table entries for two or more adapters match a destination IP
    address, the system uses the one with the lower associated "metric"
    value. It never uses the one with the higher metric.

    By default, Windows XP assigns a lower metric to the faster (wired)
    connection and a higher metric to the slower (wireless) connection.

    I think that XP and 98 are doing different things in your testing
    because of what happens when you disconnect a network cable from a
    wired network adapter: XP automatically deletes all route table
    entries associated with the network adapter, and 98 doesn't.

    So, with the wired adapter disconnected, XP automatically uses the
    only connection that has route table entries: the wireless one.

    And, in the same circumstances, the route table entries for the wired
    adapter are still there, so 98 tries to use that adapter (even though
    it isn't connected) instead of the wireless one.

    How do you disable the wired adapter on 98? I'm not aware of any
    Windows command to do that.

    If the adapters had dynamic IP addresses, you could use Winipcfg to
    release the address for one adapter, which would remove that adapter's
    route table entries and cause Windows to use the other adapter.
    --
    Best Wishes,
    Steve Winograd, MS-MVP (Windows Networking)

    Please post any reply as a follow-up message in the news group
    for everyone to see. I'm sorry, but I don't answer questions
    addressed directly to me in E-mail or news groups.

    Microsoft Most Valuable Professional - Windows Networking
    http://mvp.support.microsoft.com

    Steve Winograd's Networking FAQ
    http://www.bcmaven.com/networking/faq.htm
     
    Steve Winograd [MVP], Apr 23, 2005
    #3
  4.  
    Mike MacSween, Apr 24, 2005
    #4
  5. I tried to explain that in the following paragraph:

    For example, I just set up two network adapters in the same subnet on
    my Windows XP computer. The relevant route table entries for Internet
    access (default routes) are:

    Destination Netmask Gateway Interface Metric

    0.0.0.0 0.0.0.0 192.168.123.252 192.168.123.102 30
    0.0.0.0 0.0.0.0 192.168.123.252 192.168.123.222 20

    The first entry is for a wireless adapter with IP address
    192.168.123.102. The second entry is for a wired adapter with IP
    address 192.168.123.222. Both adapters access the Internet through a
    router on the network with IP address 192.168.123.252. Both adapters
    have subnet masks of 255.255.255.0.

    The system will always use the wired adapter for Internet access,
    because its metric (20) is lower than the metric for the wireless
    adapter (30). It will only use the wireless adapter for Internet
    access if the route that uses the wired adapter is removed from the
    route table, e.g. if the wired adapter is disabled or disconnected.

    One additional note: if the route table entries for two adapters have
    equal metrics, the system will choose one adapter or the other, and it
    will always choose the same one.
    Ah, I see. You removed the TCP/IP protocol binding from the card,
    which removed the route table entries for that card. Removing and
    adding the TCP/IP binding require a reboot, don't they, making the
    process very inconvenient?

    Windows XP can disable a network adapter without having to disconnect
    it, remove TCP/IP from it, or reboot.
    You're welcome, Mike Here are some web sites for more information:

    http://support.microsoft.com/?id=140859
    http://www.microsoft.com/technet/community/columns/cableguy/default.mspx
    http://www.microsoft.com/resources/...Windows/XP/all/reskit/en-us/prcc_tcp_qpzj.asp
    http://www.microsoft.com/resources/...00/server/reskit/en-us/cnet/cnbc_imp_ukfj.asp
    --
    Best Wishes,
    Steve Winograd, MS-MVP (Windows Networking)

    Please post any reply as a follow-up message in the news group
    for everyone to see. I'm sorry, but I don't answer questions
    addressed directly to me in E-mail or news groups.

    Microsoft Most Valuable Professional - Windows Networking
    http://mvp.support.microsoft.com

    Steve Winograd's Networking FAQ
    http://www.bcmaven.com/networking/faq.htm
     
    Steve Winograd [MVP], Apr 24, 2005
    #5
  6. Steve

    Thanks for your help, again.

    I'm spending a bit more time on this than I ought to. I'm not a network
    admin, a database developer really. But I still ought to know this.

    So, to sum up. It's possible to 'have' 2 network adapters installed in the
    machine and on the same subnet. Physically installed and configured. But
    depending on OS this may or not 'work' (by which I mean one of them will
    work). Windows XP seems to cope, Win 98 doesn't.

    But whether the adapters (or rather one of them) 'works', that is to say can
    send IP traffic, or not, the OS will only ever use one of them.

    Nevertheless the Win XP machine, with 2 adapters, both on the same subnet
    responded to pings on both of them. Presumably that's the OS's way of
    saying, 'this adapter is here, but that doesn't mean I'm going to use it'.

    Yes, I think the Win 98 machine needed a reboot. Perhaps if I set it up to
    get an IP from a DHCP server then this might get what I want - which is to
    have the wireless and ethernet adapters installed, so I can use either when
    I want. I might try that and see how it works.

    In the very small amount of this I've done, setting up this network of 4
    machines, and at clients, I've usually steered away from DHCP, simply
    because I find it useful to have fixed IPs. For instance to VNC out to
    client machines from a server at customers sites. Or even remotely.

    Yours, Mike
     
    Mike MacSween, Apr 24, 2005
    #6
  7. Mike MacSween

    Guest Guest

    Hi - this is all very useful stuff for me. I have very similar problem, save
    it's a W98 laptop that won't work wireless. Can't ping any network IP from
    it wireless, although every node on network can ping it. Plug it back into
    the wired network and suddenly it can ping again.... I posted more detail on
    this on 16 April - but alas I've not generated this quality of response.

    If any expert here has the time to look at my posting (titled One Way
    network) I'd be very grateful.

    Thanks

    M
     
    Guest, Apr 24, 2005
    #7
  8. You're welcome, Mike. This is a complicated subject, and it's not
    easy to find or understand documentation on it. One good source is
    the Windows 98 or XP Resource Kit.
    It's possible to have 2 (or more) network adapters on the same subnet.

    When you disconnect the cable from a wired network adapter:

    Windows XP notices that it's disconnected and stops trying to use
    the adapter.

    Windows 98 doesn't notice that it's disconnected and may continue
    to try to use the adapter.
    The system will only use one of them for outgoing TCP/IP traffic to a
    particular destination IP address. It decides which one to use based
    on entries in the route table that match the destination IP address.
    I think that Windows 98 and XP work the same in this respect. Both
    adapters can receive incoming traffic, such as pings, simultaneously.
    The route table doesn't apply to incoming traffic.
    Yes, it's convenient to have a fixed IP on a computer that's acting as
    a VNC server.
    --
    Best Wishes,
    Steve Winograd, MS-MVP (Windows Networking)

    Please post any reply as a follow-up message in the news group
    for everyone to see. I'm sorry, but I don't answer questions
    addressed directly to me in E-mail or news groups.

    Microsoft Most Valuable Professional - Windows Networking
    http://mvp.support.microsoft.com

    Steve Winograd's Networking FAQ
    http://www.bcmaven.com/networking/faq.htm
     
    Steve Winograd [MVP], Apr 24, 2005
    #8
  9. Mike MacSween

    Guest Guest

    Again, these posts are really helpful for me too. Now knowing how W98
    handles NICs, I've found out that simply by IPCONFIG /Release for the wired
    NIC will now allow the wireless NIC to route out.... Fantastic!

    Thanks for all your help.
     
    Guest, Apr 24, 2005
    #9
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