Help with a simple networking problem, please

[SezMe]

This is probably really simple for you network guys, but I am stumped. Here is the setup:

I have a desktop machine I use as my main software development machine. It is not on a network (I am self-employed and I use a dial-up modem for internet access). I do have a NIC which has its IP address set at 10.0.0.1 and Subnet mask set at 255.0.0.0 This machine runs Win2K/SP4.

I also have a laptop that I take with me to client sites (it also is running Win2K/SP4). I use this laptop to do work at client sites, to upload new files to their network and download files from their network to my laptop. Obviously I have a NIC in the laptop. When I am at a client site, I set the TCP/IP properties to "Obtain an IP address automatically" and have had no problems at any of my client locations.

Back at home, I connect my laptop to my desktop via a null modem cable. I just reset the IP address to 10.0.0.2 on the laptop and the two machines happily talk to each other and I can transfer files back and forth easily. I have successfully used this setup for more than 4 years...until yesterday.

Now the two machines won't recognize each other. When I try to map a network drive from the laptop to the desktop, the laptop will struggle with the request then finally give up and say (essentially) I can't find the other computer. When I do this, I can watch the little icons in the system trey try to talk with each other, but without success.

I have rebooted both machines several times. I have pulled and reinserted the null modem cable at both ends. Both systems say the NIC is working. Both systems say their status is "connected". No other hardware has been installed or changed. But now I can't get the two machines to talk to each other.

Look, I'm not a hardware or network guy. I just do bits and bytes with software. What possibly could be wrong and how can I proceed with further testing to isolate the problem? And, more importantly, to fix it.

Thanks in advance.

 

[Wudang]

Windows can be pretty flakey if you don't use the default 192.118.1.1 etc addresses (or whatever they are). Don't ask me why. I've configured TCP/IP on AIX, Sun, OS/2 and other platforms with no problems. And a null modem cable isn't really the way to do it, spring a couple of bucks for an ethernet hub.

 

[Darat]

This is probably really simple for you network guys, but I am stumped. Here is the setup: ...snip...

Look, I'm not a hardware or network guy. I just do bits and bytes with software. What possibly could be wrong and how can I proceed with further testing to isolate the problem? And, more importantly, to fix it.

Thanks in advance.

Do you have a software firewall installed on either or both PCs? If so I'd suggest switching it off on both PCs when you try to connect (obviously don't leave it off when you are on line).

 

[RayG]

It could be something as simple as a bad cable.

Instead of a hub, I'd spend the extra and get a 1 gb USB data stick. (unless you absolutely, positively, HAVE to lug around the laptop)

RayG

 

[Fungrim]

It might be worth trying with different IPs once. Say 192.168.0.1 and 192.168.0.2 with netmask 255.255.255.0. The 10.*.*.* block is often used by the internet provier (at least in sweden). My connection for example has the internet provier DNS server on 10.0.0.1. If your modem connection automatically gets its connection properties it may be that your internet provier have changed server IPs and that's why your desktop gets confused.

 

[a_unique_person]

Has your machine been renamed or put in a different workgroup or windows domain? This can happen when you have to connect to a client site. Try browsing the 'whole windows network'.

Also, just try pinging the IP address, to see if that works.

 

[MRC_Hans]

Mmm, some time ago, I hooked together my two machines, one running W98, the other running XP, with a twisted Ethernet cable, and I just couldn't get them to connect. Turned out on of them was case sensitive on the computer name (I forget which), the other wasn't, but converted the name of the other to all caps . Once I entered it as all caps in both ends, everything was OK.

BTW, this weekend, I'm going to add a wireless router to that configuration and add a laptop to the LAN, so whish me luck .


Hans

 

[ShowMe]

Back at home, I connect my laptop to my desktop via a null modem cable.

You mean an ethernet crossover cable? Null modem cables work off of serial ports. And would have nothing to do with IP numbers.

I do have a NIC which has its IP address set at 10.0.0.1 and Subnet mask set at 255.0.0.0 This machine runs Win2K/SP4.

So far, so good.

I just reset the IP address to 10.0.0.2 on the laptop and the two machines happily talk to each other and I can transfer files back and forth easily. I have successfully used this setup for more than 4 years...until yesterday.

This is one of those problems that can drive you insane until you figure it out, then it all seems so simple. I would try, in order:

If you are running XP and have recently put on a service pack, check to see if your firewall is turned on.

Make certain your subnet mask is the same on both systems.

Ping the machines from one to the other, by IP Address and by name.
If you get no reply either way, replace the ethernet cable, then check the NIC on you desktop. Since you laptop works on client site you know its NIC is good.

If it replies via IP number and not by name, check your HOSTS file to see if there is a machine name that happens to be the same as your desktop or laptop name.Check the HOSTS file on both systems.

If it replies to both IP number and by name, then your laptop may not be in the same domain/workgroup. Or the account you log in with (probably Administrator?) has different passwords between your laptop and desktop. If you do a start->run-->\\machinename\c$ (where machinename = the name of the machine you're trying to connect to) and it prompts you for a login name and passowrd, that's your problem.

Virus scan & spyware scans are always a good idea. Run those to make certain you haven't picked up something unclean.

Check and verify that you don't already have a connection to the drive you're trying to map. If you set up H: on client site to connect to one of their systems and you're trying to connect H: to something else on your home PC this can cause it to error out. Especially if you're running XP on the laptop.

Let us know how you fare.

 

[scribble]

My stupid question

Doesn't windows have some way to display it's routing table? WOuldn't that be the first thing to check?

 

[Wudang]

You could try
arp -a
on both boxes.

 

[Underemployed]

On the desktop machine (that has the internet connection), turn ON the internet connection sharing feature. This will turn it into a DHCP server (lite). Leave the laptop permanently on automatically assigned IP and as long as they are both on the same workgroup, have no firewall issues and the hardware for both (including cable) is good, you should have no problems.

 

[SezMe]

Do you have a software firewall installed on either or both PCs? If so I'd suggest switching it off on both PCs when you try to connect (obviously don't leave it off when you are on line).

Ding, ding, ding. Darat wins the kewpie doll.

I have McAfee firewall installed on the desktop machine and I did do a major upgrade a while ago. That upgrade must have changed some setting that did not allow the laptop in.

Thanks for all your ideas and, especially thanks, Darat. I owe you a cold one.

 

[kevin]

Ding, ding, ding. Darat wins the kewpie doll.

I have McAfee firewall installed on the desktop machine and I did do a major upgrade a while ago. That upgrade must have changed some setting that did not allow the laptop in.

Thanks for all your ideas and, especially thanks, Darat. I owe you a cold one.

I had this same problem at my father's house, but being the tinker he is -- each machine had a firewall from a different manufacturer. Some had McAfee, some had Microsoft's XP SP2, and a third one I don't remember. Figuring all that out was a hassle.

Oh, and I'm on my way to his house to drop off a SUSE 10.0 Linxu DVD and an Ubuntu Linux CD. So he can play some more.

Sometimes I envy people with technologically inept parents.