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

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

Mike MacSween - 23 Apr 2005 10:42 GMT

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

Reply to this Message

Kurt - 23 Apr 2005 18:50 GMT

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

> 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
[quoted text clipped - 40 lines]
>
> Yours, Mike MacSween

Reply to this Message

Steve Winograd [MVP] - 23 Apr 2005 23:16 GMT

>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
[quoted text clipped - 40 lines]
>
>Yours, Mike MacSween

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.

Signature

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

Reply to this Message

Mike MacSween - 24 Apr 2005 07:19 GMT

> No version of Windows can use two network adapters in the same subnet
> at the same time.

I'll take your word for it. Though I still don't understand why not. I've
seen 'no 2 adapters on the same subnet' often, but no explanation as to why
not.

> Each network adapter has associated entries in the route table. When
> route table entries for two or more adapters match a destination IP
[quoted text clipped - 11 lines]
> So, with the wired adapter disconnected, XP automatically uses the
> only connection that has route table entries: the wireless one.

Thanks, that all make sense

> 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.

From the user interface. IIRC Settings, Control Panel, Network, then I just
deleted the entry for TCP/IP->name of ethernet card.

> 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.

by dynamic IP addresses you mean DHCP?

Thanks, Mike

Reply to this Message

Steve Winograd [MVP] - 24 Apr 2005 08:52 GMT

>> No version of Windows can use two network adapters in the same subnet
>> at the same time.
>
>I'll take your word for it. Though I still don't understand why not. I've
>seen 'no 2 adapters on the same subnet' often, but no explanation as to why
>not.

I tried to explain that in the following paragraph:

>> 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.

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.

>> By default, Windows XP assigns a lower metric to the faster (wired)
>> connection and a higher metric to the slower (wireless) connection.
[quoted text clipped - 18 lines]
>From the user interface. IIRC Settings, Control Panel, Network, then I just
>deleted the entry for TCP/IP->name of ethernet card.

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.

>> 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.
>
>by dynamic IP addresses you mean DHCP?

Yes.

>Thanks, Mike

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/documentation/Windows/XP/all/reskit/en-us/Def
ault.asp?url=/resources/documentation/Windows/XP/all/reskit/en-us/prcc_tcp_qpzj.
asp
http://www.microsoft.com/resources/documentation/Windows/2000/server/reskit/en-u
s/Default.asp?url=/resources/documentation/Windows/2000/server/reskit/en-us/cnet
/cnbc_imp_ukfj.asp

Signature

Reply to this Message

Mike MacSween - 24 Apr 2005 09:04 GMT

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

Reply to this Message

Steve Winograd [MVP] - 24 Apr 2005 10:42 GMT

>Steve
>
>Thanks for your help, again.

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.

>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.
[quoted text clipped - 3 lines]
>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.

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.

>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.

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.

>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'.

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, 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.

Good.

>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.

Yes, it's convenient to have a fixed IP on a computer that's acting as
a VNC server.

>Yours, Mike

Signature

Reply to this Message