Server not found - FireFox in Mozilla Software

Server not found - FireFox in Mozilla Software http://www.dslreports.com/forum/r23298402 en Tue, 09 Feb 2010 23:33:58 EDT Tue, 09 Feb 2010 23:33:58 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23416213 HD_Ride : Thanks for looking into this issue:

WinXP Pro/SP2 (32bit) no IPv6 installed
network.dns.disableIPv6 –false
network.dns.ipv4OnlyDomains – blank
network.dnsCacheEntries – 1000
network.dnsCacheExpiration -3600]]> http://www.dslreports.com/forum/remark,23416213 Mon, 30 Nov 2009 18:44:27 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23409613 jmorlan : See: »IPv6 FAQ
--
This is not a rehearsal.]]> http://www.dslreports.com/forum/remark,23409613 Sun, 29 Nov 2009 12:01:15 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23409518 Willy :

said by jmorlan

:

...... whether you have IPv6 installed.

I'm afraid I don't know what that is.
How do I check for it and how do I get and install it if it's not installed?
Thanks]]> http://www.dslreports.com/forum/remark,23409518 Sun, 29 Nov 2009 11:34:59 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23409384 jmorlan : Those reporting this problem:

Please state your operating system and whether you have IPv6 installed.

Also report if you have the following entries in about:config and their values.

network.dns.disableIPv6
network.dns.ipv4OnlyDomains
network.dnsCacheEntries
network.dnsCacheExpiration

Thanks.
--
This is not a rehearsal.]]> http://www.dslreports.com/forum/remark,23409384 Sun, 29 Nov 2009 10:49:14 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23408104 HD_Ride : same here just after getting 3.5.5. On one site it was so bad I was unable to use the shopping cart’s add & remove, I had to go back to IE to complete the transaction. I just started using the Better Privacy add-on after the 3.5.5 upgrade so I thought it was that because when disabled its more manageable however I’m still getting allot of disconnects..... ]]> http://www.dslreports.com/forum/remark,23408104 Sat, 28 Nov 2009 22:06:09 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23406774 FalconX : Not this is not an isolated problem. I know for a fact that many users are affected. What's disappointing is that there is absolutely no acknowledgment from firefox team that this problem even exists. It's actually one of the most annoying problem I've experienced and you won't know how annoying it is unless you have it. Having said that, I gave Chrome a try and it's not much better. Chrome has its own "resolving host" problem that slows down websites. But I like firefox because of the extensions anyway. Unless some other browser comes along that allows for so much user customizations and useful extensions, I will stick with firefox despite this problem. ]]> http://www.dslreports.com/forum/remark,23406774 Sat, 28 Nov 2009 15:09:41 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23406768 Willy : :)Thanks for the reply.
I'm fully aware that with all the possible combination of hardware and software there will be problems.

I was trying to fix this for weeks before before I posted here on September 24, 09 about this problem.

For me, that's enough, it's not worth my time to play any more with settings.
As of now IE works fine and is much faster, but I'm still opening FF every now and then looking for an update that may clear this problem.

I'm using FF right now, ver. 3.5.5, to see if the update helps.
IE has something like 65% of market share and FF25%.
All I was saying is if Mozilla wants to beat out IE they need to work improving compatibility for whatever percentage of users are having problems.

Steve]]> http://www.dslreports.com/forum/remark,23406768 Sat, 28 Nov 2009 15:08:34 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23406698 goalieskates : While AB wasn't diplomatic, I have to agree with the point made - I run XP Pro SP3 with FF and a boatload of addons and have absolutely no problem with server not found errors - unless the server in question goes down. There's a nifty little addon for that too, btw.

So to Willy - if switching to IE or Chrome makes you happier, then more power to you. I'm not convinced from what you've written that the problem lies with FF - it could as easily be a symptom of a problem elsewhere. But absent substantive information on what makes your setup different from the rest of us, there's really no help to be given, and no benefit to repeated declarations that you give up.

I hate that you're frustrated - but it's equally frustrating to have to try to use ESP to get to the bottom of what makes your system unique. Best of luck.]]> http://www.dslreports.com/forum/remark,23406698 Sat, 28 Nov 2009 14:42:09 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23404795 Willy : Right.

*sigh*]]> http://www.dslreports.com/forum/remark,23404795 Fri, 27 Nov 2009 22:43:53 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23404758 AB :

said by Willy

:

It's my obligation to to figure out why Firefox doesn't work properly on, not only my Vista laptop, but my XP Pro desktop too?

If you want to use it, then yes, I suppose it is.

. . I'm not a Mozilla tester and I personally don't want to screw with this any more.

Then don't. Don't screw with it, don't use it, uninstall it and don't install it anymore.

I told you I believed you had the problem. That, however, puts you in a very low-percentage minority.
One 'fix' in your case is to do what you're going to do-- not fool with it anymore.

But you're claiming this is a specific Firefox issue, and I'm saying that can't be the case because millions of us use the Firefox browser without this issue.

So yeah-- *if* you want to use Firefox, then, in your case, it appears that in fact it's *you* that needs to work harder and not the people at Mozilla.

You claim Firefox has "this many problems". I claim it doesn't.

Luckily for all of us, there are several browsers available for download from different software makers. Using Firefox or any other browser is strictly a user's choice.

--------------------------

*Edit- To clarify that I responded to and quoted what you posted prior to your edit.]]> http://www.dslreports.com/forum/remark,23404758 Fri, 27 Nov 2009 22:33:10 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23404677 Willy : I didn't suggest they "blow it all up" or "start from scratch" but I'm not a Mozilla tester and I personally don't want to screw with this any more.

It's not my obligation to to figure out why Firefox doesn't work properly on, not only my Vista laptop, but my XP Pro desktop too.

Past versions ran fine and future versions may also run fine but this version is causing some people, including me some problems.]]> http://www.dslreports.com/forum/remark,23404677 Fri, 27 Nov 2009 22:09:46 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23404613 AB :

said by Willy

:

I think if Mozilla wants to win the browser market it's them, not me, that needs to work harder.

I'm sure they'll be happy to blow it all up and start from scratch to resolve some issue that affects only a handful of people.
Because it's kind of tough to believe the other millions of Firefox users are content to do their surfing with a browser that only connects to websites on a part-time basis.

I believe you have the problem, for whatever reason.
But I also know I get a 'server not found' error only once in a great while, and that behavior has been typical of any of the large number of Firefox versions which I've used over the past few years.]]> http://www.dslreports.com/forum/remark,23404613 Fri, 27 Nov 2009 21:49:42 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23404424 RedMatrix : I agree with @Willy

although the network.dns.disablePrefetch has lowered my errors significantly, it is now only happening 10% of the times. (rather than 90%)
--
~Dave~]]> http://www.dslreports.com/forum/remark,23404424 Fri, 27 Nov 2009 20:48:18 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23404056 Willy : Thanks for posting that FalconX.
I hope that solution works out for you and anyone else that wants to try it.

Personally I'm not interested in a program with this many problems since IE works just fine.

I think if Mozilla wants to win the browser market it's them, not me, that needs to work harder.]]> http://www.dslreports.com/forum/remark,23404056 Fri, 27 Nov 2009 19:10:39 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23403330 FalconX : Hey all,

I had this problem for probably about 3 months. I think I may have resolved for now. I haven't gotten the server not found error in two days and hopefully it won't come back. I don't think it has anything to do with add-ons so don't waste your time disabling them.

Follow the firefox uninstallation guide here and completely remove all traces of firefox from your system.
»www.tweakguides.com/Firefox_3.html
Go to your network connection/local area connection/properties and uninstall TCP/IP v.6 protocol.
Reboot.
Install Firefox 3.6 Beta 4. Disable dns.ipv6 in about:config. Restart firefox. ]]> http://www.dslreports.com/forum/remark,23403330 Fri, 27 Nov 2009 15:46:32 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23394377 ironwalker : Have not been following the small updates for 3.5, but, my friend who decided to re-install 3.5 yesterday said all is fine again and the dns issue is gone....mind you it has only been a day.

He will keep me posted, I am sure.

Anyone who has had this issue, tried again with a newer FF3.5 series, and has it working now, please let us know.

Thank You
--
Live Free or Die!
www.sidux.com
www.chronixradio.com

]]> http://www.dslreports.com/forum/remark,23394377 Wed, 25 Nov 2009 12:23:22 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23394335 Willy : I was having the problem on my laptop with ver 3.5.30729 while I was away.

I'm back on my desktop, same version, no problems.
I 'm baffled.]]> http://www.dslreports.com/forum/remark,23394335 Wed, 25 Nov 2009 12:17:42 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23392404 bcool : was experiencing same problem on 3.5.5. I would immediately try same address in IE8, boom! Right there. Anyway, just installed 3.6 b3 and no such problems so far :uhh:
--
"in flagrante delicto"]]> http://www.dslreports.com/forum/remark,23392404 Wed, 25 Nov 2009 00:47:17 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23387282 bombadill : I finally gave up on Mozilla totally. After ditching FF I finally turfed Thunderbird out for the same reason; failure to connect.

Pity. But surely someone from Mozilla MUST know that right now they've got a dud on their hands. :mad:

And I still think that Google search engines might have something to do with it. ;)

"Puts on tin hat and walks sadly into an MS sunrise" :huh:]]> http://www.dslreports.com/forum/remark,23387282 Tue, 24 Nov 2009 03:15:22 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23387067 imtim83 :

said by Joewashere :

Ya same problem. 3.5.3 was doing it very often. Upgraded to 3.5.5 and problems is less frequent than 3.5.3, however it is very annoying.

Always happens when you use a combination of open in new windows and new tabs. By the 20th time, causes server not found across all the windows and all the tabs.

Only restarting windows clears it up. Reset of modem and router does nothing.

I have a clean install of XP, Office 2007, and the latest McAfee firewall/virus scanner.

Mozilla team please FIX asap.

I wish it was that simple. Can't count on my fingers how many time I formatted and reinstalled Windows 7 64 bit trying to fix this problem. Well over 20. I know a little overboard but the problem was driving me crazy and I thought it was me. Glad it wasn't. Still it keeps me up at night wanting to fix it lol. I guess it is the inner computer geek in me.]]> http://www.dslreports.com/forum/remark,23387067 Tue, 24 Nov 2009 01:05:52 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23386951 anon : Ya same problem. 3.5.3 was doing it very often. Upgraded to 3.5.5 and problems is less frequent than 3.5.3, however it is very annoying.

Always happens when you use a combination of open in new windows and new tabs. By the 20th time, causes server not found across all the windows and all the tabs.

Only restarting windows clears it up. Reset of modem and router does nothing.

I have a clean install of XP, Office 2007, and the latest McAfee firewall/virus scanner.

Mozilla team please FIX asap.]]> http://www.dslreports.com/forum/remark,23386951 Tue, 24 Nov 2009 00:37:20 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23352360 imtim83 :

said by bombadill

:

Doesn't work. Did that still getting total crap from FF latest version.

For what it's worth let the GURUS ponder this one

As far as I know I don't have ANY Google crappy tools anywhere.

BUT as FF runs back up again after a complete clean reload, as I use it more and more, in the far LH top tab I get long Google search string rubbish as it tries to load the address. THEN I get the "Server Not Found" message.

FF has fallen into the crap pit. I'm going back to MS. When I call up an address with MS there's NO Google search strings, just an instant lock on the address.

YOU GO FIGURE.

Goodbye FF.

Yep]]> http://www.dslreports.com/forum/remark,23352360 Tue, 17 Nov 2009 02:49:33 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23352324 bombadill : Doesn't work. Did that still getting total crap from FF latest version.

For what it's worth let the GURUS ponder this one

As far as I know I don't have ANY Google crappy tools anywhere.

BUT as FF runs back up again after a complete clean reload, as I use it more and more, in the far LH top tab I get long Google search string rubbish as it tries to load the address. THEN I get the "Server Not Found" message.

FF has fallen into the crap pit. I'm going back to MS. When I call up an address with MS there's NO Google search strings, just an instant lock on the address.

YOU GO FIGURE.

Goodbye FF.]]> http://www.dslreports.com/forum/remark,23352324 Tue, 17 Nov 2009 02:22:51 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23340494 mens rea : I had the same "Server not Found" error. I ran CC to clean cache cookies etc in FF. I then backed up my bookmarks and completely uninstalled FF 3.5 including the profile folder. I then did a clean install, including any extensions, imported my bookmarks and the problem seems to have resolved itself. If anyone chooses to try this remember browsing history, stored passwords and cookies will all be removed.]]> http://www.dslreports.com/forum/remark,23340494 Sat, 14 Nov 2009 11:06:56 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23331057 Willy : Yep I tried it, didn't help.]]> http://www.dslreports.com/forum/remark,23331057 Thu, 12 Nov 2009 12:35:02 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23328420 ironwalker :

said by Willy

:

I found this to address this problem:

Where you would type in a url, type about:config, then ENTER"
Set network.dns.disablePrefetch to True
- right click in your about:config
- choose New-> Boolean
- type network.dns.disablePrefetch , click Ok
- choose true, click Ok

I just changed the setting and will see what happens.

I saw that the day I installed 3.5 and had the issue....doesn't help.
Its a codeing problem somehow.
--
Live Free or Die!
www.sidux.com
www.chronixradio.com

]]> http://www.dslreports.com/forum/remark,23328420 Wed, 11 Nov 2009 21:54:50 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23327526 Ronnie_USA : I have also been having the very same problem.]]> http://www.dslreports.com/forum/remark,23327526 Wed, 11 Nov 2009 19:02:56 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23327484 Willy : I found this to address this problem:

Where you would type in a url, type about:config, then ENTER"
Set network.dns.disablePrefetch to True
- right click in your about:config
- choose New-> Boolean
- type network.dns.disablePrefetch , click Ok
- choose true, click Ok

I just changed the setting and will see what happens.]]> http://www.dslreports.com/forum/remark,23327484 Wed, 11 Nov 2009 18:56:00 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23327476 Oleg : Works for me in both Firefox and IE.]]> http://www.dslreports.com/forum/remark,23327476 Wed, 11 Nov 2009 18:55:00 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23327265 bombadill : From way down in Aus. me too.

FF is really starting to make any venture into the net a real pain.

I'll go back to IE8 and wait for a fix to both FF AND Thunderbird which is giving the same unable to connect message as FF.

I'll stick with Thunderbird because of my large address lists and archived emails. Too much hassle (yet) to move back to MS. But if it doesn't get better I'll have to go backwards. :(]]> http://www.dslreports.com/forum/remark,23327265 Wed, 11 Nov 2009 18:05:21 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23311346 Willy : If you find a solution let me know.
I'm probably just going to use IE for a while.]]> http://www.dslreports.com/forum/remark,23311346 Sun, 08 Nov 2009 18:32:47 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23306618 JTM1051 :

said by Willy

:

I prefer Firefox to IE but I'm getting a message "Sever Not Found" way to much. ...

I've also been getting quite a few of the same server not found messages since updating from 3.0.15 to the 3.5.x versions (currently using 3.5.5)

Generally I always do a clean/fresh install when doing updates other than minor version/patch updates. Due to the new project I'm working at in downtown LA (leave the house at 4:45AM and get home around 6:00PM), have not been on the home PC much, and I just downloaded and installed Fx 3.5.1 over 3.0.15. One of the weekends when I have the time/energy I'll do a fresh/clean install and hope it helps solve or at lest lessen the problem.

For me generally happens more frequently after browsing different sites, and appears more often when I do a middle(wheel)-click on a link in a page to open in a new tab. The temp workaround I've been using is to use the MR TECH Clear Memory/Disk Cache toolbar button prior to clicking on page links.

BTW one evening after browsing with Fx, I did try browsing for awhile with IE 8 and Opera 10 and did not experience any DNS server not found problems.]]> http://www.dslreports.com/forum/remark,23306618 Sat, 07 Nov 2009 14:19:00 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23306577 imtim83 :

said by ironwalker

:

What version of firefox are you useing, seems to be a problem dns wise with firefox 3.5 and above.

Bingo]]> http://www.dslreports.com/forum/remark,23306577 Sat, 07 Nov 2009 14:07:30 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23305453 Willy : Version 3.5.5]]> http://www.dslreports.com/forum/remark,23305453 Sat, 07 Nov 2009 08:17:56 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23304868 ironwalker : What version of firefox are you useing, seems to be a problem dns wise with firefox 3.5 and above.]]> http://www.dslreports.com/forum/remark,23304868 Fri, 06 Nov 2009 23:56:59 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23303955 Willy :

said by JohnA

:

You did post it there, Willy. Someone had it moved here.

So I was told.
Now it's in the Mozilla Forum.
I didn't know this was here.

Anyway, I disabled "Add-Ons" and reset "Tool Bars and Controls"

I did these one at a time and it didn't help.

Edit:
I've gone and disabled all each item in safe mode one at a time.
FF is better but not 100%

FYI, I deleted the cache each time I opened IE or FF

Most noticeable is how much slower FF is than IE8.]]> http://www.dslreports.com/forum/remark,23303955 Fri, 06 Nov 2009 19:36:14 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23303778 JohnA :
You did post it there, Willy. Someone had it moved here.]]> http://www.dslreports.com/forum/remark,23303778 Fri, 06 Nov 2009 18:52:29 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23303195 Willy :

said by darcilicious

:

:D

Yeah, :huh:]]> http://www.dslreports.com/forum/remark,23303195 Fri, 06 Nov 2009 16:33:40 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23303123 darcilicious : :D]]> http://www.dslreports.com/forum/remark,23303123 Fri, 06 Nov 2009 16:20:07 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23303117 Willy :

said by darcilicious

:

If you have problems with Firefox and not with IE, then you can safely assume the problem is not with FiOS -- it couldn't care less which browser you're using.

Follow the rest of the advice and start up Firefox in safe mode.

@$%&, I don't believe this.
I didn't realize until you mentioned FIOS I posted in the wrong Forum.

I meant to post this in the Software forum because I always thought it was a FF problem.
I am a FIOS subscriber but I'm on a Brighthouse network right now in Florida.

I'm really sorry for the confusion and I plan start using FF tomorrow and run it in safe mode.
In spite of my screw up the info here is really addressing directly the problem I'm having.
Thanks]]> http://www.dslreports.com/forum/remark,23303117 Fri, 06 Nov 2009 16:19:06 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23302860 darcilicious :

said by Willy

:

I'm not using NoScript.
I've been using IE yesterday and today with no problems

Tomorrow I'll go back to FF and see what happens.

If you have problems with Firefox and not with IE, then you can safely assume the problem is not with FiOS -- it couldn't care less which browser you're using.

Follow the rest of the advice and start up Firefox in safe mode.]]> http://www.dslreports.com/forum/remark,23302860 Fri, 06 Nov 2009 15:23:55 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23302838 Willy : I'm not using NoScript.
I've been using IE yesterday and today with no problems

Tomorrow I'll go back to FF and see what happens.]]> http://www.dslreports.com/forum/remark,23302838 Fri, 06 Nov 2009 15:19:09 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23302640 Raphion : I had a problem recently with FF not loading pages completely or at all, and it turned out to be a conflict between NoScript and a FF update. I updated to newest NoScript and the problem vanished.

Check FF in it's safe mode (no extensions) to see if it's one of them. Then if it is, disable one at a time and narrow it down.]]> http://www.dslreports.com/forum/remark,23302640 Fri, 06 Nov 2009 14:44:29 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23299179 Willy : I just changed my default FF to IE and give it a couple of days and see what happens.
It's almost impossible to have a FF session and not have at least one or two Server not found messages so any better results with IE should be easy to spot.]]> http://www.dslreports.com/forum/remark,23299179 Thu, 05 Nov 2009 21:58:57 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23298689 darcilicious : This is at least the third thread opened in the last couple of days mentioning surfing problems; and I wouldn't be at all surprised to find out that it's related DNS.

Try changing the DNS servers to the ones from »opendns.com/ You can do it for just your computer to see if it helps and if it does, then you can actually configure your router to use them instead as well.]]> http://www.dslreports.com/forum/remark,23298689 Thu, 05 Nov 2009 20:22:28 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23298594 Willy : I did a google search "Global warming facts"
Opened 2 pages, about 20 links, and 1 page gave me an eror.
Dis the same thing with Firefox and got three Server not found messages.]]> http://www.dslreports.com/forum/remark,23298594 Thu, 05 Nov 2009 20:02:55 EDT Re: Server not found - FireFox http://www.dslreports.com/forum/remark,23298415 nwrickert : I'm pretty sure that's a DNS lookup problem. It should affect IE as much as it affects firefox.

If you try with firefox, then try with IE, it is possible that the DNS server was slow responding, but the answer is in cache by the time that you try it with IE. This makes it look like a firefox problem. But if you start first with IE, then try firefox after a failure, it might look like an IE problem instead.
--
AT&T Uverse; Zyxel NBG334W router (behind the 2wire gateway); openSuSE 11.0; firefox 3.0.15]]> http://www.dslreports.com/forum/remark,23298415 Thu, 05 Nov 2009 19:27:39 EDT Server not found - FireFox http://www.dslreports.com/forum/remark,23298402 Willy : I prefer Firefox to IE but I'm getting a message "Sever Not Found" way to much.
Forget the address in the image, it's one of the many sites I was trying to open when I decided to do a screen capture.
[att=1]
I can click on "Try Again" and eventually the page loads.
I don't seem to have this problem with IE8

Any ideas out there to what the problem is and how I can fix it?

]]> http://www.dslreports.com/forum/remark,23298402 Thu, 05 Nov 2009 19:24:50 EDT