DNS server issue with internet access issue.

Posted on 2011-09-02
Last Modified: 2012-05-12

We have recently has a leased line installed and i am in the process of migrating all our network services over to the new line from our old ADSL line.

We use a watchguard x510 FW: 11.4.1 we use webblocker for internet filtering

I have a problem with our DNS whereby all at least once a week i get no external dns resolution.
Internal resolution is fine but i cant resolve say some websites seem to work but i have only found one or two.

The dns servers are replicating fine and from looking at the firewall dns resolution is predominatly done by one server.

When the problem occurs i restart the dns server service and it seems to work ok. No entries in the eventvwr which look like they need attention.

I am strugglig to troubleshoot the issue as im not sure where else to look.

Domain is a 2008 functional level.

Your help is appreciated.
Question by:HousingSolutions
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LVL 10

Accepted Solution

cjrmail2k earned 500 total points
ID: 36472362
have you got DNS forwarding enabled? Also, try and forward to a couple of DNS sources offered by your provider in case they have an issue upstream.

Expert Comment

ID: 36478055
What are your DNS forwarders? Are all your PC's using the same internal DNS Server to resolve external DNS?
LVL 27

Expert Comment

ID: 36487730
you havent run spybot or something like that on your server have you? those things are known to add stuff to your 'hosts' file which can upset some DNS servers.
If restarting the DNS server on the server fixes it it seems like the server is the best place to start though.

what dns forwarders does the dns server have?
can you contact them directly during the issue (use NSlookup server <ip/name of external DNS>)

on a PC, do IPconfig /all during the issue and check if the DNS servers are still as expected. if not, you may have something else on your network sending out dhcp. seems unlikley if DNS server restart fixes, but is worth checking.
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Author Comment

ID: 36488192
Hi all,

I dont think there was anything in the DNS forwarders box. so i have added one of the servers to the list. I guess this could have been causing the problem but how on earth was it resolving before?
It dropped out this morning so will wait and see what happens.
LVL 27

Expert Comment

ID: 36488512
if no forwarders are set, the DNS server resolved the address itself using root hints. this can take more processing so most companies set up a forwarder to allow someone elses DNS do the work for them.
This could have been a cause but seems a bit odd.
Give it a go and see if this helps.

Author Comment

ID: 36488559
can i configure more than one server as a forwarder? I only have two internal dns servers.
LVL 10

Assisted Solution

cjrmail2k earned 500 total points
ID: 36488631
yes you can, you would forward from you internal dns servers to a list of external servers. Usually 2 servers from your provider are enough
LVL 27

Expert Comment

ID: 36489770
Agreed. U can add loads of forwarders but two is normally plenty.

Author Comment

ID: 36535296
Hi guys i finally got to the botton of this. For some reason the server i had set as a forwarder wasnt working too well. so i changed the server that performs the forwarding to the other DC in the domain and now not only is the internet more stable it is also quicker as dns requests are getting served more quickly.

Thanks guys.

Author Closing Comment

ID: 36535299
Pointed me in the right direction. great help and thanks.

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