The Math Stack Exchange site said "We are Offline" until I reset my router - Why?

Question

When I navigate to the URL math.stackexchange.com using my home Internet connection, I receive the "We are offline for maintenance" webpage. This does not happen for any other Stack Exchange website, as proven by my being able to write this question right now.

It has been like this for several days, and began when there was some sort of maintenance 4 or 5 days ago. I have cleared my cache and all other browsing data, and I also receive this message on my mobile device if I'm connecting to my wireless network.

However, if I use the cell network to connect to the Internet, I can visit the website just fine, and similarly with my office Internet connection, I can visit the website.

Is this clearly a problem on my end, or could it be a problem with my ISP? Does anybody have suggestions?

EDIT: I did one further test and found that it cannot be my ISP. I set up a proxy to another server, and then ran my browser through that, and I still got the "We are offline" message. This gave me the suspicion that it might be my router, and indeed, upon resetting my router, I could finally visit math.stackexchange. So now, my updated question is: How did this happen?

Answer 1

It's a DNS caching issue. I ran into the same issue on the main stackoverflow.com site using Firefox. Firefox was continuing to get 503 errors upon accessing the site, but other browsers (which I don't normally use and which I certainly didn't use to access the site when it was actually under maintenance) and curl were able to load the site just fine.

I couldn't convince Firefox to clear its DNS cache, but after quitting and restarting it, Stack Overflow loaded correctly again.

Not sure if this is a browser bug, but either way it adds up to a terrible user experience (site is actually up but appears to be down, and no amount of refreshing/waiting short of a browser restart fixes it). At the very least, I'd suggest to the SE devs to put up a message on the maintenance page (http://sstatic.net/Sites/stackoverflow/app_offline.htm, for reference) suggesting that the user also try restarting his browser if there's no update on the status blog.