DNS confusion

November 26, 2005 2:01 PM

Why would a new domain (registered today) work on Firefox on one computer, but not on the other, when they're both on the same DSL connection?

I registered a new domain on Dotster today. To my surprise, the domain propagated quickly and in 30 minutes I was able to access the site through Firefox. I was able to set up the site, configure mysql, install SMF, and a bunch of other stuff, all of which used the new domain name.

So I turn to my other computer to see what it looks like in Firefox. It says "Looking" then pops up the dialog "__ could not be found. Please check the name and try again." But it works fine on other Internet sites. IE reports the same error. FTP and Telnet also don't recognize the domain name. I checked the spelling carefully.

Going back to my first computer, it still accesses the site great; no problems.

It's almost as if the computers are using totally different DNS servers. However they're on the same network (same router, which connects to a DSL modem and on to Sprint DSL service). I looked under Firefox to make sure no proxies were selected, and they both report a direct connection to the Internet.

The problem is more puzzling than annoying... any ideas what is happening here?

posted by shannymara to computers & internet (8 comments total)

try
ipfconfig /flushdns
in a dos window (or the run... box in the start menu)
posted by andrew cooke at 2:07 PM on November 26, 2005

Very interesting... that worked (ipconfig, not ipfconfig). Now I'll have to figure out why it worked. Thanks!
posted by shannymara at 2:20 PM on November 26, 2005

oh sorry for the typo/brainfart (a similar command is called ifconfig on linux).

the computer has a cache of dns lookups so that it's not constantly connecting out to request the same information aain and again. you probably checked on that computer before the name was available and it cached the failure (which seems a bit odd to me, i must admit - you'd think it would only cache successes).
posted by andrew cooke at 2:26 PM on November 26, 2005

It's called 'negative caching'; BIND does it too. It makes sense because a 'failed' lookup is not an error in the usual sense; it's really a successful lookup that has returned the response 'doesn't exist'.

In other words, there's a DNS server saying 'I have authority for this zone, and I can authoritatively confirm that the name you're looking for doesn't exist', which is as valid a response as 'that name does exist, and here's the IP address', and hence worth caching. Here's the RFC.

In Windows you can turn off negative caching permanently by going to

HKEY_LOCAL_MACHINES\SYSTEM\CurrentControlSet\Services\DNSCache\Parameters

in the registry, and setting 'NegativeCacheTime' to 0.
posted by chrismear at 2:41 PM on November 26, 2005

heh. thanks.
posted by andrew cooke at 2:49 PM on November 26, 2005

That's bloody useful, Chris. Thanks.
posted by blag at 3:34 PM on November 26, 2005

On my Windows computers, I turn off the "DNS Client" service, because networks I'm on always have real DNS servers.

I find the local client makes things harder to troubleshoot, so I just disable it entirely.
posted by Malor at 3:58 PM on November 26, 2005

I find the local client makes things harder to troubleshoot, so I just disable it entirely.

I don't know if I'd advise this, though, because the local cache is going to be a lot faster than your local DNS server's response. In most cases, it works fine, and his problem would have eventually resolved itself anyhow, after the default time had expired.
posted by hoborg at 7:32 PM on November 26, 2005