Several months ago, I upgraded my wireless router to a Linksys WRT110, which supports a (draft) version of the 802.11n protocol. Everything worked well out of the box – as you would hopefully expect – until today, when I tried to upgrade the firmware. I'd been having some odd trouble with DNS queries getting handled in unexpected ways; that and a couple other things that I noticed led me to suspect that my router might conceivably be the source of the problems. So I upgraded my firmware from the 1.0.02 that it had shipped with to the 18.104.22.168 available on the website here.
Big mistake. Turns out that this version of the firmware can't handle multiple connections to the router, which of course is sort of the point of a router. If only one computer was connecting, the router would stay up and work just like you'd expect. But as soon as a second computer (say, my desktop upstairs) tried to connect, the router would go completely silent: it wouldn't route traffic or respond to pings or answer HTTP management requests.
Apparently this problem isn't necessarily universal with the 22.214.171.124 firmware, but it's been reported again and again on the Linksys discussion forums ever since Cisco first posted the 126.96.36.199 firmware back in May, and Cisco still hasn't done anything about it.
The solution, I found, was to downgrade the firmware. Cisco won't let you download the older 188.8.131.52 firmware from the WRT110 support page, but they will let you download it from the WRT100 support page. I downgraded the older firmware, and all was well (unless you count the two hours I lost troubleshooting the problem, of course).
[Updated 2/15/09: Cisco has removed the 1.0.02 firmware from their main site (linksysbycisco.com). The above link points to an alternate version of their website, which as of 2/15/09 still has the old --good -- software. I've also copied it up to my website in case they remove it again. Cisco also has the source for all the versions of their software posted here, but I'm not enough of a Linux hacker to get it to compile, and I'm not sure you should trust my version if I did.]
This is the second day this week that I've been astonished at the poor choices made by very large, well-funded, reputable companies.
On a side note, this would have been an interesting time to try one of the open-source firmware options (here or here, among others), but apparently the WRT110 is based on an Ralink platform instead of the more common Broadlink, so the drivers aren't available as of yet.
[Update 7/2009: Apparently the best drivers to use are the recently released 1.0.05. They can be downloaded here: http://www.linksysbycisco.com/US/en/support/WRT110/download. As mentioned above, do not use 184.108.40.206. I don't know why it took Cisco so long to fix this problem.]
[Update 10/2009: Folks are still reporting problems with the 1.0.05 firmware, and I've run into them myself. I'm backleveling my own router to the 1.0.02 firmware available (among other places) here. This whole situation is bizarre.]
[Update 3/2010: Since the last time I'd looked, Cisco posted a 1.0.07 version of the firmware on the WRT110 support page. I tried it, but it ended up breaking (of all things) certain Subversion operations. I've since backleveled to 1.0.02. Again. Huh.]