jawtheshark's Journal: Windows 7 and the conflicting IP address

You probably remember the Dell L502x, I bought for 525€ in June last year. Well, during my days off at Christmas I finally got around setting the Windows 7 installation (100GB partition, the rest goes to a real OS) to my tastes After the initial horror of actually installing Windows 7 (Topic only tangentially touched in the second paragraph), most of it went well. I even managed to find out how to make default profiles without using sysprep. I'm running Limited User (Standard User in Win7 lingo), and all works well as generally software is now behaving correctly without rights.

There is one thing, though, that irritated the hell out of me. For this you first have to understand my network infrastructure. I have no consumer end router and a Soekris net5501-70 running OpenBSD does all my routing needs, including DHCP and bind. The works. As I like to limit the spread of bare IP adresses over the system, I basically configure my own bind serving up the "sharks" domain (at my parents it's "jungle"). Everywhere, where it's allowed, I use the names of the machines and this includes DHCP. So, for example the entry for wobbegong (my PostScript printer) looks like this:

host wobbegong { # Wired:
hardware ethernet 00:00:74:91:10:62;
fixed-address wobbegong.sharks;
}

This means that the device with MAC address 00:00:74:91:10:62, receives the IP associated with wobbegong.sharks, which is currently 192.168.2.193. If I want to reorder my private IPs, I just need to adapt the zone file and I'm pretty much done. (This has happened, I used to have the same subnet as my dads network, but I changed it so I can get a VPN running between our networks someday)

Traditionally, I have used fixed IP addresses for all my machines, but once I learned DHCP, I switched to statically assigned IP addresses for all non-guest machines. This is useful in the sense that I don't need to do dynamic DNS internally. For example, I want to take a file from tiger.sharks, while at work? No problem, ssh to jawtheshark.com, ssh from there to tiger.sharks and I can get what I need. It doesn't happen often, but it's damned useful.

Now, what happens when you have two NICs in a device which is very common for laptops: wireless and wired. Well, I do something that most people do not expect, but it works and makes no problems whatsoever. I simply assign the same IP address to both interfaces. It looks like this:

host requiem { # Wired
hardware ethernet 14:fe:b5:b4:d4:6f;
fixed-address requiem.sharks;
}

host requiem { # Wireless
hardware ethernet bc:77:37:c8:c2:fb;
fixed-address requiem.sharks;
}

This is no problem when you're only on wireless, you get an IP address and it works. This is also no problem if you're on wired and have wireless disconnected, because, well, there still is only one single interface used with one IP address. Now what happens if you allow both to connect. Mayhem? Cats and dogs sleeping together?

No, it also works and the reason is that the wireless is slower than the wired interface. At that point something called "Metrics" are used. Basically, the system says "look, I have two NICs, both with the same IP address and I'm simply going to use the quickest one".

Well, I say this works, because it does work on Windows XP, it also works on OS X and it works on Linux. Windows 7, simply refuses to assign the IP to the wired interface. I guess this is pure chance, because I first connected using the wireless interface.

Manually setting the IP or forcing DCHP to give out another IP address works and it then even detects it's basically the same network. In that stupid "Network and Sharing Center": they get grouped.

Okay, I understand, I do something weird. My mistake, I'm stupid. Someone who thinks like me will now say: "No problem, you want to use wired, so disconnect from wireless and let it take the IP address on the wired, it's just Windows 7 acting up and being prissy". That's where the big surprise came.... I did exactly that, disabled the wireless, plugged in wired and.... nothing... It did not want to take the IP address the DHCP server gave it (which was the same as the one on the -now disabled- wireless interface). It stubbornly kept telling me it was an "unknown network".

Seriously? I do understand I do something weird and it's some fringe case (but, hey, seems to be technically 100% legal) However, not accepting the same IP address on a different interface that is NOT active is simply not acceptable.

Seems that due to Windows 7, I will now have to re-engineer my network. Bah, it's only for the occasional game. Probably won't bother too much. Still, in my eyes, this is a bug. A big, big bad bug.

Update 2012-01-06@22:21CET
If you wonder, for now I just set the wireless interface to full dynamic. It gets a different IP and then it works. Well, not 100%. It wouldn't want to be fixed during runtime, I was forced to reboot. Well, not that Windows told me to, but after waiting and waiting and clicking "Diagnose" half a dozen of times, it still wasn't working. Reboot? Instant fix! I retried then with identical IPs and rebooted but that resulted in the same problem. So for now, dynamic wireless and fixed wired.

Multi-homing

[Short Circuit]

I'd be surprised if Windows 7 didn't support multi-homing.

My network's a little different. I have separate /27s for my wired and wireless networks.

Re:

[jawtheshark]

Well, I was surprised as it works everywhere else. Maybe it's only supported on Professional and/or Ultimate. This is Home Premium. Try it out and see what happens. Fact is: it doesn't want to do what I want. (Yes, the correct name is Multihoming...) Why? I do not know.

Re:

[kesuki]

my sister had a network problem with windows 7 wireless, she used a push button networking router and the wifi router only worked on one machine, so i tried fixing it manually instead of with a setup cd, only windows 7 refused to connect to the network because it had a memory of the old broken network login, i finally had to rename the router, in order to get networking working again with her kids phones and ipods or whatever they have i used my kindle to verify wifi was working on multiple devices.
i don't

Re:

[jawtheshark]

There must have been some real boneheads working on the networking part, I think. Other weird stuf: a while ago, I replaced the gateway at my parents. The only thing that changed from the perspective of the client PCs was the new IP address of the gateway. The only Windows 7 machine we had back then, my fathers laptop, considered it a whole new network. Why? I can't simply fathom why....

Re:

[jawtheshark]

I'm not alone [windows7forums.com]. While a slightly different situation, it points to the root cause as the default gateway being the problem.

Re:

[Short Circuit]

You should look into IPv6 SLAAC. It wouldn't have this problem. ;P

Re:

[jawtheshark]

Yeah, yeah, IPv6 is on my list "to do". First the basics got to work, then I can get to the exotic stuff.

Re:

[Short Circuit]

IPv6 SLAAC is the first step beyond simply getting connectivity from upstream or via a tunnel...and it's very, very easy. I highly recommend Tunnelbroker.net [tunnelbroker.net] and Hurricane Electric's IPv6 cert process [he.net]. It just about walks you through getting a basic working setup. Catch me via email, and I'll walk you through the rest.

Re:

[jawtheshark]

I don't want a tunnel. I want real IPv6 and my ISP has it, but OpenBSD doesn't do autoconfig on routers so I need my own block. I asked one, but they don't offer any yet. So, I wait...

Re:

[Short Circuit]

What are they passing around for a prefix?

Re:

[jawtheshark]

Dunno... Really, I haven't looked much into it. I guess I can look that up on RIPE. I saw it in my logs once, but I can't find it right now.

Re:

[Short Circuit]

What's the name of the ISP?

Re:

[jawtheshark]

They are called Visual Online [www.vo.lu] and have AS9008. Their website IPv6 is 2001:1610:0:2::75, so I assume it will be along those lines.

They have been doing IPv6 native for a long time, the old instructions are here [www.vo.lu], but obviously it's for their "supported" routers. I really dislike all consumer end router even if FritzBoxes are perhaps a bit better than the average, it still doesn't compare to full control. All their new routers come with IPv6 fully enabled. I refuse to use them. My needs are not those of a

Re:

[Short Circuit]

It sounds like all you need is to have a DHCPv6 client listening on your wan interface.

I don't like DHCPv6, personally, but it does things SLAAC won't. Still, if you get a DHCPv6 client up and running, your router, at least, will have native IPv6. You'll have to take the prefix it gives you and chop it up slightly for internal redistribution. Don't have time to google, now, but they should at least distribute a /56, if not a /48.

Re:

[jawtheshark]

Last time I checked, no DHCPv6 on OpenBSD in the default packages. :-( As it's PPPoE, I tried with the HISADDR6 option, but ppp in userland isn't IPv6 ready either. I'm not fully up to date, I run 4.8 and 5.0 is out and it has some very nifty features. My hopes are now on my dads connection as he gets FTTH (well, he has it, but the ONT isn't installed yet) on the 16th January 2012 and I so want to play with that. I can't get it at my apartment and it also won't be available where I build. Bummer. :-(

I am suprised my network works at all

[tqft]

your problem looks like a bug and smells like a bug, but is it exploitable? If so maybe MS might fix it.

Given that MS next monthly patch is next Tuesday and is looking biggish, maybe wait until after then and see if the problem persists.

Re:

[jawtheshark]

It might also be in the name of security.... I mean, two identical IP addresses? Perhaps a man-in-the-middle is going on, right? I mean, why would anyone want to do this, eh? That's how they think, I think.