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I have a laptop with Windows 7 and an older stationary with Windows XP. When I had a screen I set it up for use with remote desktop. I no longer have any screen, and used to connect to it using remote desktop, but that is a few years ago, and LAN details might have changed. When I connect the old computer to the network and boot it up, I cannot see it in the network browser, I don't know its name, its network group name or its IP address.

How can I sniff the network to discover it (should I use a cross-over cable directly?) and get back to using remote desktop?

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4 Answers 4

up vote 3 down vote accepted

The best solution would be to borrow a monitor and attach it to the XP computer long enough to get it going and verify that it is working OK.

Do you have a Hi-Def TV? Does it have a VGA port on it? You could use that for a monitor.

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As much as it's not in the spirit of the question, this IS the best solution. –  Shinrai Dec 22 '11 at 18:36
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If that computer gets its address via DHCP, check your router's web interface, it might say what IP addresses are given out by DHCP. Try these one after another.

If that comptuter has a static address, get a network sniffer, like Wireshark, it's free and works on Windows/Linux. Connect two computers with crossover cable. Any packet you see in the sniffer that has a source IP address different from your "good" computer's IP, will be the IP address of the other computer.

However: It seems you cannot be even sure that troubled computer boots properly. So if you don't see any network traffic, it probably means that computer didn't boot properly, so you need a display to troubleshoot that.

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+1 for suggesting that the computer/OS may not be booting properly. –  Ƭᴇcʜιᴇ007 Dec 22 '11 at 18:22
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There should be a set number of possible ip addresses on your home network. Probably 254 possible addresses. Running a ping scan against these should result in your finding the system correctly.

I used to have a batch script that would do this for me mostly automatically using just the windows command line tools, but I can't recall what it was at the moment. Give me a bit.

Ah hah!

nslookup is probably the easiest one to use. Using a batch script with a FOR loop to scan each number from 1-254 and appending that to the rest of your home network IP address (192.168.1. and outputting the results to a text file, you'll end up with a list of each and every host on your network. Gimme a couple more mins and I'll see if I can remember the syntax for that script I used.

Eh. Not finding anything that'll make it easy enough.

For the time you could put into this I'd just go get Zenmap (http://nmap.org/zenmap/) and scan your local network subnet. I'll find the computers there and should make it pretty clear which one is the headless system.

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Ping the broadcast address of your network then check your arp cache for it's mac address. The Mac address should be physically labeled on the board/card.

For example: 192.168.1.254 would be the broadcast on the 192.168.1.0/24 network. So if you have a subnet of 255.255.255.0 (which most home networks do) your broadcast is .254. So for my example ping 192.168.1.254 -t and let it run for a minute or two (it will say, "destination host unreachable" but it is working...). Then run the Command arp -a and you will get a list of active hosts on your network. Now check the list for the mac address of the network card on the missing pc and you have found your PC.

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I'm curious, what if local subnet is different? Say the laptop is on 192.168.0.1 but the PC was on 192.168.7.1 (lots of router/modems have non-standard default subnets). Is there any way to find those? –  mtone Dec 22 '11 at 18:25
    
Then it wouldn't work as this only works at layer 2 on the OSI model.. However while alot of routers may have "non-standard subnets" (your words) not many have multiple subnets with DHCP service for multiple subnets... And if you do have multiple subnets, it's something your purposefully did and would know about. Or you would need to actually have two routers on your network... –  Kyle Dec 22 '11 at 18:31
    
Not to mention it's all the same router so just give your self an IP on the 192.168.7.0/24 network then ping 192.168.7.254... –  Kyle Dec 22 '11 at 18:32
    
I agree local networks usually use the same subnet. I was refering to adding a new or unused device to the existing network, with conflicting subnets making it undiscoverable. For instance, I once bought an old used DSL modem/router, without documentation, that was set to 192.168.7.1, while my network was on 1.1. If it wasn't that I luckily found a few forum posts mentionning the default subnet, I wonder if I could have ever found its IP. –  mtone Dec 22 '11 at 20:43
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