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I have a laptop running Windows XP SP3 with a wireless NIC and a wired NIC. I bridge the two network connections under Windows\Control Panel\Network Connections. This gives me a single bridged network connection. DHCP is enabled on this bridged connection and everything functions as expected on the laptop as though I had a single wireless DHCP enabled connection.

I want to connect a desktop PC with only a wired NIC to the same network as the laptop. It appears that I wrongly assumed that the Windows Bridging feature would act as basic layer two switching device with the added function of translating from wireless to wired. The first thing I tried to do was attach the desktop PC to the laptop with DHCP enabled on the desktop PC. But when I try this I get an IP conflict on both the laptop and the desktop PC. Why doesn't this work?

The only way I can get the desktop PC to access the network correctly (with this particular setup) is to manually configure the IP address of the desktop PC. Why does this work but enabling DHCP doesn't?

This may or may not be relevant but to get the bridge working at all I had to force the wireless NIC into 'promiscuous mode' as described in this article.

Someone did mention (on another site) that it might be something to do with MAC address masquerading. But why would MAC masquerading be implemented by the bridge? And if this is the case how can it be turned off?

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1 Answer 1

Greeting from Peru. I've come across the same issue a couple of days ago. I've been reading about it everywhere on the net so i can understand what's going on and how microsoft bridging works. According to a video I found, they say that this kind of solution works as a Layer 3 bridging. So the source mac addresses are changed. So what i imagine is that when the bridge interface is enable the first thing it does is to send a dhcp discovery message and then the dhcp server gives it one and keeps a table of the leased ips.

MAC of Bridge 12:34:56:78:90 ----------------- IP 192.168.1.10 ( For instance )

Then, when the wired computer on the other side request for an ip address it goes through the bridge and the bridge changes the source mac address for its own mac address (12:34:56:78:90) and when the dhcp server receives it , it checks the table and gives back the same ip ( 192.168.1.10 ). The bridge proceses it and sends it back to the wired pc on the other side and maybe that's why we have an ip conflict issue. I sorry about my english. I'm not very good at it. But i hope i can make my point.

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