Vista and the DHCP Broadcast flag

I failed to note this earlier: my adventure with Windows Vista has begun in earnest. Most things moved over without pain, but network services have taken much longer than expected… I’m sure I’ve already mentioned my network setup before. Upon upgrading Roberta’s laptop to Vista (decided to start with that as it had the software and hardware complement that was least expected to cause problems), the computer was no longer getting its IP number automatically. A short while later, with tcpdump in good use, it was clear that the offer was being sent, but the machine was somehow ignoring it.

A google search later, and it became clear that the newly written stack on Vista used the broadcast flag from the standard. However, Microsoft’s documentation indicated that if that was causing problems, it was the server’s fault, not Vista’s… They did offer a couple of registry hacks that would resolve that, so I figured there would be no harm in trying. After consulting one of our networking gurus on campus, we agreed it would be ok to give that a shot. So I did. But it didn’t. Work, I mean. Everything remained stubbornly as it was…

It took me a long time, much longer than it should, to finally resolve the issue a few minutes ago. Having been googling this for a while, it was clear that I was the only one having this problem. Or talking about it at least. Needless to say, this can only mean one thing: when the omniscient Web has no knowledge of a problem, then the one you’re experiencing can only be caused by yourself. It turns out that my server’s broadcast replies were being sent as originating from the localhost IP address, so Vista’s replies would simply never get back to the server. Stupid misconfiguration, which only affects broadcast replies. After adding the requisite “server-identifier” address in the various pools, things are finally back to normal.


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