Why can't I see a computer on my network?

A few weeks ago, I set up a home network using a Linksys BEFW11S4
Router. My desktop(call it A) is directly connected to the router.
I have a second desktop (call it B) connected via a Wireless PCI card
and a laptop directly connected. The laptop is for work and has a
different group name than the other two computers and can't be seen by
either computer A or computer B, which is expected..

Until recently, I could access computer B from computer A. Now I
can't. They both belong to group MSHOME. Computer B has no problem
sharing the internet connection, but if I ping computer A from it, I
get no response. WEP is enabled and I checked the encryption and it
looks correct on both ends. Boith are enabled, 64-bit, with the same
encryption key. If I check the DHCP clients table, computer A shows up
and so does the laptop, but not computer B. Also, I cannot ping
computer B from computer A.

I can't think what else to check. I can't think of what I could have
done to change the network configuration. I'm at wits end. What am I
missing?

"Sandy" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> A few weeks ago, I set up a home network using a Linksys BEFW11S4
> Router. My desktop(call it A) is directly connected to the router.
> I have a second desktop (call it B) connected via a Wireless PCI card
> and a laptop directly connected. The laptop is for work and has a
> different group name than the other two computers and can't be seen by
> either computer A or computer B, which is expected..
>
> Until recently, I could access computer B from computer A. Now I
> can't. They both belong to group MSHOME. Computer B has no problem
> sharing the internet connection, but if I ping computer A from it, I
> get no response. WEP is enabled and I checked the encryption and it
> looks correct on both ends. Boith are enabled, 64-bit, with the same
> encryption key. If I check the DHCP clients table, computer A shows up
> and so does the laptop, but not computer B. Also, I cannot ping
> computer B from computer A.
>
> I can't think what else to check. I can't think of what I could have
> done to change the network configuration. I'm at wits end. What am I
> missing?

If you cannot ping between computer A and B there is a layer 3 or lower
problem. Double check the WEP mode and key including the key ID I think
there's 4 to choose from for 64bit. Check the router doesn't have access
control set up if so ensure the MAC address of computer B is there.

You must find the problem at layers 2 or 3 before you try and play with the
upper layers that windows uses.

Check the subnet mask of the machines to ensure they are both on the same
network.

"Paul Landregan" <(E-Mail Removed)> wrote in message
news:bl1p0f$7b9ib$(E-Mail Removed)...

> If you cannot ping between computer A and B there is a layer 3 or lower
> problem. Double check the WEP mode and key including the key ID I think
> there's 4 to choose from for 64bit. Check the router doesn't have access
> control set up if so ensure the MAC address of computer B is there.

I don't think this can be his problem because he said...

> Computer B has no problem sharing the internet connection.

Doesn't this imply his wireless link to the router is working OK?

But then he says..

> If I check the DHCP clients table, computer A shows up
> and so does the laptop, but not computer B. Also, I cannot ping
> computer B from computer A.

So how can B be connecting to the Internet if it isn't getting an IP address
from the router/DHCP?

It all seems a bit inconsistent, or have I missed something?

"Sandy" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)
>
> I can't think what else to check. I can't think of what I could have
> done to change the network configuration. I'm at wits end. What am I
> missing?

Confirm that my understanding is correct: Both A and B can surf the 'Net at
the same time with no difficulties. However, neither has knowledge of each
other.

If that is correct, are you sure that B is actually using your router to
access the 'Net? You said that the DHCP client table for your router is not
showing B, but B can surf the net. The likely causes of this are: 1) B has
a static IP address or 2) B is on a different router. If B has connected to
a neighboring access point, it would be on a separate network and wouldn't
be able to ping any of your PCs.

Use the wireless network configuration tool to verify the access point in
use by your wireless card. Your configuration utility should allow you to
set the desired access point to be used. If the one in use is not yours,
set it to be yours and yours only. (Or, set it to be primarily yours, then
use the other one as backup for when yours is out.

If you are indeed on another access point, take this as an object lesson in
why you should secure your own wireless network. If you do not wish to
allow unfettered access to your LAN and/or Internet connection, take this
opportunity to review your security settings.

I recommend the following:
1. Disable DHCP or at least restrict the pool of IP addresses to the
specific number of PCs on your LAN.
2. Disable SSID broadcast on your access point.
3. Enable MAC address filtering using the MAC addresses of your PCs' NICs.
4. Enable encryption (WEP, but WPA is better, if available for your
devices).

These steps should be sufficient to protect most home networks from all but
very determined hackers.

And if your neighbor has an open network, why would they bother with
yours...?

--
Lenny

On Fri, 26 Sep 2003 16:46:21 GMT, "Lenny Toulson" <(E-Mail Removed)>
wrote:

>>Confirm that my understanding is correct: Both A and B can surf the 'Net at
>the same time with no difficulties. However, neither has knowledge of each
>other.

That is correct. Both computers can surf the net, but have no
knowledge of each other. I don't know if it matters, since as a
previous poster suggested, my problems may be below the Windows layer,
but computer A is running XP Pro and computer B is running Windows 98.
>
>If that is correct, are you sure that B is actually using your router to
>access the 'Net? You said that the DHCP client table for your router is not
>showing B, but B can surf the net. The likely causes of this are: 1) B has
>a static IP address or 2) B is on a different router. If B has connected to
>a neighboring access point, it would be on a separate network and wouldn't
>be able to ping any of your PCs.

It has to be using the router. There is no other access to the
internet. I checked the network config andit is using Dynamic IP
addressing.

>Use the wireless network configuration tool to verify the access point in
>use by your wireless card. Your configuration utility should allow you to
>set the desired access point to be used. If the one in use is not yours,
>set it to be yours and yours only. (Or, set it to be primarily yours, then
>use the other one as backup for when yours is out.

Okay, now you lost me. How do I determine the access point?

From each computer browse to http://checkip.dyndns.org/

Do both of them show the same IP address? If they do then both are
connected through your router. If not, one of them is connected
through somebody else's wireless network.

wk

On Fri, 26 Sep 2003 17:20:30 +0100, "Paul Landregan"
<(E-Mail Removed)> wrote:

>>Check the subnet mask of the machines to ensure they are both on the same
>network.


Okay, that may be the problem. the subnet mask of computer A is
255.255.255.0. The subnet mask of computer B is 255.0.0.0. How to I
fix this?

"Sandy" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Fri, 26 Sep 2003 17:20:30 +0100, "Paul Landregan"
> <(E-Mail Removed)> wrote:
>
> >>Check the subnet mask of the machines to ensure they are both on the
same
> >network.
>
>
> Okay, that may be the problem. the subnet mask of computer A is
> 255.255.255.0. The subnet mask of computer B is 255.0.0.0. How to I
> fix this?

If this has been DHCP set then your looking at two different
routers/wireless networks. Are the actual IP's similar eg 192.168.1.1 and
192.168.1.2 or totally different eg 192.168.1.1 and 10.1.1.1.

If the subnet mask is set manually then right click in network neighbourhood
to get to network properties, goto TCP/IP properties and enter the correct
Subnet mask

"Sandy" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Fri, 26 Sep 2003 17:20:30 +0100, "Paul Landregan"
> <(E-Mail Removed)> wrote:
>
> >>Check the subnet mask of the machines to ensure they are both on the
same
> >network.
>
>
> Okay, that may be the problem. the subnet mask of computer A is
> 255.255.255.0. The subnet mask of computer B is 255.0.0.0. How to I
> fix this?

Also try this on each computer, go to a command prompt. Start, Run then type
Cmd.

Type Ipconfig /all this will reveal all the IP information you need
including the ip address of the serving DCHP server. if they are different
thn you have a problem, your latched to somebody else's network.

On Fri, 26 Sep 2003 19:03:04 +0100, "Paul Landregan"
<(E-Mail Removed)> wrote:

>If this has been DHCP set then your looking at two different
>routers/wireless networks. Are the actual IP's similar eg 192.168.1.1 and
>192.168.1.2 or totally different eg 192.168.1.1 and 10.1.1.1.

Nope, the IPs are the same 192.168.1.1

>If the subnet mask is set manually then right click in network neighbourhood
>to get to network properties, goto TCP/IP properties and enter the correct
>Subnet mask

The IPs are assigned dynamically, so I can't change the subnet mask.