DHCP: Quick connection with a cross-over

Let's say we have Mary's laptop and Brian's laptop. Brian has a 6 GB movie file on his hard disk that he wants to transfer to Mary.

Both laptops have a NIC with an ethernet port, so obviously it would be a good choice just to connect them with a cross-over cable and use something like FTP or Samba to send the file across.

Anyway, before any file sending can be done, both machines have to sort out their IP address. Because Brian and Mary regularly plug their laptops into different networks to access the internet, they both have DHCP set up for their NIC.

So anyway getting to the crux of it...

We hook them up with a cross-over cable. We run the DHCP client on one of the machines. There's no response because there's no DHCP server, and so the machine adopts a random address in the network 169.254/16. (This is what DHCP is supposed to do if it doesn't get a response from a DHCP server, right?)

We run the DHCP client on the other machine, and again we get a random address in 169.254/16.

Running Windows, we then just go into network neighbourhood and viola there's the other person's computer. Or if using FTP, we can do "ipconfig/all" on each machine to get their IP address, then just do

But here's what I want to ask: Is this method of using "DHCP failure" reliable for giving the machines IP addresses with which they can communicate? Is it really as simple as "Stick a cross-over between them and hit DHCP on both machines"?

On another thing: Can someone please suggest a very simply free FTP server application for Windows? I've searched a bit, even downloaded and tried one or two of them, but they all seemed a hell of a lot more troublesome than they should have been.

Also another thing: If you're connecting only two computers together, would it be more efficient to use something like PPP instead of Ethernet? I'm talking about sending 10 GB files from one machine to another.

Reply to
Tomás Ó hÉilidhe
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The way I would do this, if you must use TCP/IP, is to set up both machines with a statically configured IP address first. I don't know about this 169.254/16 subnet. It could be an address that both those PCs had been using previously.

RFC 2131 says that if a DHCP server is unavailable, and the client is set up to acquire its IP address via DHCP, the client can reuse its previous IP address. However, it can only do so until the lease for that IP address expires. Then it must stop using the IP address and it must warn the user. At this pooint, I don't know of any legal way of assigning IP addresses with DHCP. You have to configure manually.

But by the way, what about using netbeui instead of TCP/IP? That should be perfect for this situation. If both machines are Windows, and you have them on the same L2 net, this has to be the best way to transfer files, no? Netbeui should be one of the protocol options you're allowed to choose from, on any Windows machine. Turn it on and see what happens.


Reply to
Albert Manfredi

If I am recalling things correctly, the 169.254/16 stuff isn't DHCP at all but IPv4's version of IPv6's stateless autoconfiguration. An entirely different set of RFC's altogether. Might all be shoved into the same bit of client code I suppose, but I'm pretty sure they are logically distinct.

rick jones

Reply to
Rick Jones

Albert Manfredi wrote in news:ea6ede24-4726- snipped-for-privacy@j78g2000hsd.googlegroups.com:

This is what I'm currently doing at the moment... I just thought it might be a little handier to set up some sort of "auto IP assigning" configuration.

It's a private IP range reserved for a failed DHCP request.

So it's no reliable after all then.

Forgive my ignorance, but I haven't a clue what nebeui is.

If you had two laptops and a cross-over cable, what would be the best way of transferring files (big files in particular, such as movies)? I know a bit about networking but not a hell of a lot. I thought it would be best to use FTP over TCP?

Reply to
Tomás Ó hÉilidhe

Microsoft "Services for Unix" is free for windows users, but it isn't simple to install. If I remember, the confusing thing is that it needs its own password file.

formatting link

-- glen

Reply to
glen herrmannsfeldt

The way everything is automated now for network setup now, I haven't looked for these details in years.

In WinXP, if you go to "Control Panel," then "Network Connections," then "Local Area Connection," click on "Properties" in the "General" tab.

You should see a checked box for TCP/IP. You might see one also for "Client for Microsoft Networks," and "File and Printer Sharing for Microsoft Networks."

I think that if you have two Windows computers connected to one another via Ethernet, you should be able to uncheck the TCP/IP box, make sure those other two boxes are checked, and then use Windows Explorer to see the folders on the other computer, copy and paste, and so forth.

Netbeui is a local printer and file sharing protocol that used to be in common use some time ago, before TCP/IP became so prevalent. It is however not a routable protocol. For local office nets, it works fine. Easy to set up and trouble free. I might be forgetting something, but in older versions of Windows, it seemed like there was a box to check that actually said netbeui.

Maybe someone on here is less vague on this netbeui stuff. To me, when we used to use it at the office, it was a no brainer.


Reply to
Albert Manfredi

May we guess that both laptops are running Windows XP ?

Then the solution is simple. At the TCP/IP property page there is a tab 'alternative configuration'. Use it to set a static number and subnet mask. E.g. for Mary and for Brian. Both with for subnet.

Booting without a DHCP server present will now take 1 minute longer. (As it does now also, using APIPA, your 169.254 address).

Whenever you boot a laptop or connect a network cable to it, the PC will look for a DHCP server. If it cannot find one (on your direct cable :-) it will assign the 'alternate' IP address.

Reply to
Gerard Bok

snipped-for-privacy@zonnet.nl (Gerard Bok) wrote in news:4788ae44.2689468 @News.Individual.NET:

This is exactly what I'm trying to avoid. Let's say the Brian is really really stupid, so Mary wants to be able to just say "connect the cable in and I'll do the rest on my own computer".

I had thought of setting up a DHCP server on my own laptop but I couldn't get a decent piece of Windows software for doing it. I tried one, but it turned out to be horribly complicated to use. I should be able to supply it simply with:

  • start address * end address * subnet mask * lease time
Reply to
Tomás Ó hÉilidhe

I fail to see your point here. If Brian really is that stupid, Brian shouldn't have any network cable connected to his laptop at all, imho.

If you mean, you only want to use something that doesn't involve any user interaction, you are basically asking 'how can I make an already vulnerable system even more vulnerable ?'

Well, actually a DHCP server is included in Windows. It's part of ICS (Internet Connection Sharing).

I'm too lazy to try it, but if you have some time at hand: Setup Mary's laptop for internet access via any means, except the network. (So, e.g. using a dialup modem or USB dongle.) Then install ICS, assigning the NIC to be the shared connection. This will set the IP address of Mary's PC to with a DHCP server for the rest of the subnet. As said, I haven't tried it, but I wouldn't at all be surprised if Mary's PC would issue a decent DHCP lease to Brian :-)

Reply to
Gerard Bok

Very normal situation and what "Rendezvous" or "Bonjour" from Apple was designed for. Two sales-weasels meet in some airport waiting area, and want to trade pr0n^H^H^H^Hsales leads.

I'm not sure it's a function of DHCP, but it's normally used in windoze and MacOS. Often, the idiot who set up the DHCP server screwed it up, and rather than expose the problem, we'll just grab some random address out of the range and pretend nothing is wrong. See RFC3927 available at your favorite search engine.

3927 Dynamic Configuration of IPv4 Link-Local Addresses. S. Cheshire, B. Aboba, E. Guttman. May 2005. (Format: TXT=83102 bytes) (Status: PROPOSED STANDARD)

Depends - assume first that the NICs are compatible (10BaseT verses

100BaseT verses Gigabit - half verses full duplex), and then that the operating system knows about this security hole protocol, and that it hasn't been disabled. Don't forget that if you are using different operating systems (say, windoze and OSX, or one of the *nix), you may run into name resolution problem. While Apple and microsoft got together to work on RFC3927, they each went their own incompatible way with name resolution, so you'll need to know how to use IP addresses rather than names. Then there may also be firewall problems on either or both systems.

Can't help there - got rid of windoze before they invented the Internet or whatever microsoft is claiming now. But this sounds as if you want normal file sharing - I thought that happened automatically unless you disabled things.

'ppp' using what interface, verses Ethernet using what protocol? 'ppp' using the serial or parallel ports is going to be very slow. USB _might_ be faster, but most systems are not configured to easily do that. On the other hand, standard Ethernet has been around since the

1970s, and virtually every operating system knows how to handle this by default.

Old guy

Reply to
Moe Trin

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