Sharing an IP address between two interfaces

Posted by: wfaulk

Sharing an IP address between two interfaces - 30/03/2007 18:56

This is in reference to Windows, but I'd be interested in other OSes, too.

Is there any way that I can get Windows to assign the same IP address to a wired and a wireless network interface so that transitioning between the two is more seamless?

One of my newest favorite Windows irritations is when Windows decides that it needs to cycle my wireless connection for no apparent reason and it decides that the IP address associated with it needs to go away. This is equivalent to unplugging a network cable and having it decide to remove your IP address instead of it being a temporary network outage.
Posted by: mlord

Re: Sharing an IP address between two interfaces - 30/03/2007 19:16

Quote:
This is in reference to Windows, but I'd be interested in other OSes, too.

Is there any way that I can get Windows to assign the same IP address to a wired and a wireless network interface so that transitioning between the two is more seamless?

One of my newest favorite Windows irritations is when Windows decides that it needs to cycle my wireless connection for no apparent reason and it decides that the IP address associated with it needs to go away. This is equivalent to unplugging a network cable and having it decide to remove your IP address instead of it being a temporary network outage.

Do what I do: configure the DHCP server to assign the same IP address for both MACs.

Cheers
Posted by: wfaulk

Re: Sharing an IP address between two interfaces - 30/03/2007 19:17

There's a variety of reasons that's a pain in the ass in my situation, but I don't even know if it will work under Windows.
Posted by: mlord

Re: Sharing an IP address between two interfaces - 30/03/2007 19:18

Quote:

Do what I do: configure the DHCP server to assign the same IP address for both MACs.


Mmm.. I wonder if your OS might allow something similar client-side: assign exactly the same MAC address to both interfaces ?
Posted by: tfabris

Re: Sharing an IP address between two interfaces - 30/03/2007 19:22

I'm able to do this with assigning fixed IP addresses on the client. Windows gripes at me each time I go into the network properties box (hey, you've got an IP address on another interface that's the same! Are you sure you really meant to do it that way?) but it works.
Posted by: wfaulk

Re: Sharing an IP address between two interfaces - 30/03/2007 19:27

Under Windows, MAC address reassignments are handled by the driver, some of which provide the facility, others of which don't. Besides, having the same MAC address on a network is bad, even if it's going to the same computer.
Posted by: wfaulk

Re: Sharing an IP address between two interfaces - 30/03/2007 19:28

Yeah, I just tried that and, for some reason, it prevents the wireless authentication from working.
Posted by: tfabris

Re: Sharing an IP address between two interfaces - 30/03/2007 19:44

Quote:
Yeah, I just tried that and, for some reason, it prevents the wireless authentication from working.

The only reason I could see that happening is if the LAN cable was plugged in at the same time you were trying to authenticate wirelessly. This little stunt only works when you use one connection or the other. You can't do both simultaneously.

Either that or the authentication was trying to go by MAC address, too, and you didn't tell the authentication server to take both the wired and the wireless mac addresses.
Posted by: gbeer

Re: Sharing an IP address between two interfaces - 30/03/2007 21:15

Quote:
This is in reference to Windows, but I'd be interested in other OSes, too.

Is there any way that I can get Windows to assign the same IP address to a wired and a wireless network interface so that transitioning between the two is more seamless?

One of my newest favorite Windows irritations is when Windows decides that it needs to cycle my wireless connection for no apparent reason and it decides that the IP address associated with it needs to go away. This is equivalent to unplugging a network cable and having it decide to remove your IP address instead of it being a temporary network outage.


If you make sure not to enable both interfaces at the same time, you should be able to assign the same IP to each.
Posted by: wfaulk

Re: Sharing an IP address between two interfaces - 30/03/2007 21:16

Yeah, I want them both up at the same time. What I want is seamless movement from wired to wireless. If there's some other way to do that, that'd be great, too.
Posted by: gbeer

Re: Sharing an IP address between two interfaces - 30/03/2007 21:36

i've never seen that before. At a guess it would take a virtual interface that dynamically enables whichever bit of hardware is to be favored. e.g. Use the wired if connected, otherwise use the wireless.

As I said, never seen that before.

Edit: After some googeling the term wanted is "Ethernet Failover".
Posted by: wfaulk

Re: Sharing an IP address between two interfaces - 30/03/2007 21:43

Okay, I was hashing this out and having both interfaces up at the same time doesn't make any sense.

Basically, all I want is something that will allow you to say that two interfaces are on the same logical network and have it use the same IP on the "best" interface, based on, first, link status, and then anything else -- speed, whatever. And it has to be application transparent.

What I mean by that is, if I lose link on my wireless connection with Windows, every long-term connection immediately bombs out, rather than waiting to see if it will regain link two seconds later. I want to be able to be using my wired interface, then unplug to walk across the room and not have any sort of hiccup.
Posted by: gbeer

Re: Sharing an IP address between two interfaces - 30/03/2007 22:18

Yep the term is failover, though none of the googel results were related to doing this on a single machine. All the results seemed to be related to the operation of servers.
Posted by: drakino

Re: Sharing an IP address between two interfaces - 30/03/2007 22:32

Short answer, no.

Not even in Vista with the new network stack.

It might be possible if you had some sort of network teaming setup and bound the two interfaces into only one that Windows sees, but I haven't dug enough to find software that will do this in a generic setup. Plenty of server NIC drivers do this though.

And having this setup on my Mac laptop for years now, I can understand why you want it. It's so nice to be able to start a file copy while on wireless, realize it's dirt slow, and go and find an ethernet cable to plug in without interrupting the transfer.
Posted by: wfaulk

Re: Sharing an IP address between two interfaces - 30/03/2007 23:45

How do you set it up on the Mac?
Posted by: wfaulk

Re: Sharing an IP address between two interfaces - 30/03/2007 23:58

Oh yeah. I guess it is just HA, just looked at from a different viewpoint. So, for Windows, that's going to be a commercial product. At least until MS incorporates a lousy version of it into the OS.
Posted by: drakino

Re: Sharing an IP address between two interfaces - 31/03/2007 00:02

Just as Mark described, my server assigns the same IP to both my wireless and wired MAC addresses.
Posted by: Attack

Re: Sharing an IP address between two interfaces - 31/03/2007 01:40

I use IBM's Access Connections program to auto switch to a from Wired / Wireless. It can even detect the SSID and auto switch to diffenent network profiles. I'm sure someone else makes something like it, try searching shellcity.net.
Posted by: mlord

Re: Sharing an IP address between two interfaces - 31/03/2007 02:16

Quote:
i've never seen that before. At a guess it would take a virtual interface that dynamically enables whichever bit of hardware is to be favored. e.g. Use the wired if connected, otherwise use the wireless.

As I said, never seen that before.


It's called a "bridge device" under Linux.

Basically, configure the wireless i/f and the wired i/f as members of a bridge, and assign a single IP address to the bridge itself, rather than to the member interfaces.

I'm sure that MS must have heard of this kind of thing already, right?
Linux has had it for (many) years already.

-ml
Posted by: tfabris

Re: Sharing an IP address between two interfaces - 31/03/2007 03:42

There is a bridge feature under windows, you just select two interfaces under network properties and rightclick and select bridge networks. Dunno if it's the same thing, I always thought it was the new way to do internet connection sharing, which is a different thing.
Posted by: tfabris

Re: Sharing an IP address between two interfaces - 31/03/2007 03:44

Ah, I see, it's a genuine network bridge.
Posted by: adavidw

Re: Sharing an IP address between two interfaces - 31/03/2007 19:46

I dunno. It just always works for me, no setup required. One of those things the Mac just does right, I guess.