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Why has my network stopped resolving certain DNS routes?

Posted on 2009-02-17
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We have an S3 account where we store the content for our website.  Yesterday, I noticed that the content isn't working, so I started looking into it.  I found out that the DNS is pointing to the correct place, and the DNS host said that the request was being blocked somewhere between our router and the host.  We put in a ticket with our ISP and they put in a ticket with theirs.  Eventually, someone found the block and removed it.

Now, our nameserver is looking to itself to find the next server in the route, but since we flushed it and deleted the cache, it has no information to resolve.  If we bypass the nameserver and set the nameserver as our ISP's nameserver, it resolves just fine.  What can we do to get it working again?  Yesterday, traceroute would get halfway and find the block, then get no response.  Now, it gets "Unable to resolve target system name content.*********.com"
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Question by:jamesbcox1980
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by:omarfarid
ID: 23661192
what happen to the hints file?
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dhoffman_98 earned 1200 total points
ID: 23661229
It sounds like your DNS server is not able to resolve the host, and that it is not the authoritative source for that domain. Therefore, it forwards the request to another DNS server and asks it to resolve.

The question sounds like two different problems are happening. First you say when you try to resolve through your name server it fails, but your ISP's name server resolves. That could simply be a matter of correcting the root hints or forwarders configuration on your name server so that it can determine where to send requests that can not be locally resolved.

DNS servers can also cache the information that they collect so that further lookups are already local. Your note says you flushed the cache so that should resolve that issue. Bear in mind though that your clients also cache some information, so I would suggest running "ipconfig /flushdns" as well on the client.


When you do a traceroute, you only need to resolve the IP address of the remote system, and at that point it either resolves or it doesn't. If it doesn't resolve, then traceroute won't even run. If it does resolve, then it will start traversing the routers from your client to the destination and hopefully show you each hop. If you are getting stuck somewhere, then it is NOT A DNS PROBLEM... it is a routing problem.

The title of your question says "stopped resolving certain DNS routes"... well that is misleading because there is no such thing as a DNS route. DNS is simply like calling 411 and asking for a phone number. You give it a host name and it gives you the number... after that, DNS is out of the picture.

Routing issues can come from several sources. It could be that a router betwee you and the ISP got a bad table entry and needs to be fixed. That is simply something you are going to have to address with your ISP and their upstream providers.
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by:jamesbcox1980
ID: 23661339
We deleted the cache, so the hints file is gone, and the server is not refreshing it as it should.  It refreshed everything but our content DNS.  We put in a ticket with Ergos as well, to make sure it wasn't their fault.  I'm going to go over your information and get back to you shortly.  Thanks.
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by:omarfarid
omarfarid earned 800 total points
ID: 23661468
the hints file should not be deleted since it contains the name servers for the top domain (.), you need to restore it from backup or copy it from another server. Please see links below which describes the hints file and show an example (you may create it manually since it is a text file):

http://www.myitforum.com/articles/16/view.asp?id=11114
http://computerperformance.co.uk/w2k3/services/DNS_root_hints.htm
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by:dhoffman_98
ID: 23662356
For future reference:
Next time you want to flush your cache, just right click it and select "Clear Cache" instead of deleting it.
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by:jamesbcox1980
ID: 23662476
Sorry, I misspoke, we did "clear" the cache rather than deleting it.  My mistake.  We have tried forcing it to refresh and copy from another server, but it isn't working.
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by:omarfarid
ID: 23662502
what you copied from other server?
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Author Closing Comment

by:jamesbcox1980
ID: 31547845
We created a new hints file and replaced the old one.  We forced a refresh and after about 2 hours it copied everything from the top server.  Apparently the file was corrupted.  Thanks to you both!
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