Hi
Thanks for your comment. At the moment we have only one network card in the server (we plan to add a second card soon), this is a fixed IP address.
Regards
Steve
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DNS Address with Static IP
Hi All
Hope yopu can help with my problem.
I have a server running SBS 2003 R2. I have it configured with a static IP address.
When a client connects we have our server acting as the DHCP server on the network. The DNS server for each client is the IP address of the server, which I understand is how it should be. The problem is that each day BT (our ADSL provider) change the 2 DNS server addresses (I think there can be up to 8 differnet ones).
As the server is acting as the DNS server for the network there have been some 'forwarders' set up to forward DNS requests to the BT DNS servers, however when the 'valid' DNS servers of the day are not at the top of the list we get problems connecting to the internet. We fix this at the moment by moving the two valid DNS servers to the top of the forwarders list.
The question I have is can I set the server up so that it gets the DNS servers automatically from the router. The option to 'Obtain DNS server addresses automatically' is greyed out (I guess it is only enabled if 'Obtain IP address automatically' is enabled).
I realise I can use external DNS servers such as openDNS...but is there a way to get my server to update its forwarders automatically, or should I set the server up in some other way to route DNS requests the the correct DNS servers.
Many thanks for reading this question.
Steve
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Answers
There are a couple of options that spring to mind:
1. BT will more than likely have a caching DNS server that doesnt change, so you could point your DNS forwarder at this address first.
2. Set primary DNS forwarder to your local router IP address, and as this always contains the correct DNS servers for BT (attained direct when connecting to BT) you will always be able to resolve DNS.
3. Dont have any forwarders, simply rely on root hints to allow you to resolve names on the internet.
I talked about caching servers because I use PlusNet myself, and they have changed their primary DNS server ip addresses before, but the caching one of 212.159.6.9 usually remains the same.
Roothints are how a DNS server obtains the result for you if it cannot find an answer either in its own zone file, or by asking another dns server (ie. your ISP server). If the ISP server does not have an answer stored (because it has had to research it for another client) then it would also use root hints to find the answer for you. Root hints are specified in Exchange by default.
It works like this... You ask for a result, it cant find it locally, so it try by looking at whether it is .com or .co.uk or whatever. It has a server listed which points it to a server which knows about all the .com names. Then it looks at the first bit of the address, say m in the case of microsoft.com. Exchange has a server which it queries for each letter of the alphabet, so if it starts m then it queries 200.22.22.2 say. And it goes through and through until it gives you the result you are after. It is called a recursive query.
So basically, it is forwarding your request to another server to find the result, but it may have to pass it backwards and forwards to more than one server to find it. The nice thing is, once it has found it for one client, it will store it for other clients.
The simplest solution to the problem will probably be to use known good (non-BT) DNS servers as your forwarders, assuming you can locate a couple that give good responses. Failing that, the easiest way to configure root hints on your server is to open the DNS console, right-click your server, and select Properties. Click the Root Hints tab. If your root hints are already configured, there will be a list of servers that look like A.ROOT-SERVERS.NET, B.ROOT-SERVERS.NET, etc., all the way through M. Their IP addresses should also be shown. If you don't see this list, the simplest way to obtain it is to click the "Copy from Server" button and input the IP address of an external DNS server. That should copy the root-hint list from that server to yours.
Occasionally, only the names of the root-hint servers will populate the list, and the IP addresses will show as unknown. If this happens, close the DNS console and wait a few minutes, then open it again and check the list. If the addresses still aren't there, you can try copying them from a different DNS server, or you can ping each one of the listed servers, get its address (assuming you've got public name resolution working at all), and edit its corresponding root-hints entry manually.
One other thing: Your own server should not appear in the root-hints list. This seems to happen fairly often, though I don't know why. If you see your server listed there, delete it from the list.
Thanks for your comments.
Here is the rub. I appear to have a fully populated root hints setup on my DNS configuration. All IP addresses are present (and the server IP address is not in the list) but I still seem to have a slow response (or a total timeout of internet explorer when browsing) if the are DNS servers in my forwarderes list that are problematic.
If I try putting the IP address of my router at the top of the forwarders list the IE just times out. If I put the current address of the BT DNS server at the top of list I get the quickest respsonse, but this address seems to swap over every day, so the next day I go back to a slow response again. OpenDNS seems to perform reasonably well if this is at the top, but I would prefer to use BT's DNS servers if possible.
So do you guys know how I can get the server to put the current DNS servers of the day at the top of the forwarders list by somehow reading it from the router, or is that just non starter?
I appreciate all your advice, sorry if my understanding of DNS is a little vague.
Regards
Steve
I would try it without forwarders at all; Remove the forwards, and test to see how the server performs when searching for DNS entires itself. The server will also cache any entries, so when one user visits www.bbc.co.uk the server will cache the result, and the next client asking for the same page will be server the result very quickly because the server can answer from its cache.
Forwarders are not essential, so give it a go without and let us know if it works well.
Hi
Sorry for the delay in getting back to you. Have taken out all forwarders and wanted to see what happened for a few days.
Everything seemed to be working OK but I had a few funnies. A couple of days ago a had a problem where www.linear.com was not accessible. I was not having problems with any other sites. It seemed unable to resolve DNS.
I looked in the DNS cached lookups for linear.com and there were to NS entrys but no A entry (as for other sites).
I switched on a forwarder to openDNS and then I could resolve this address.
I though better leave openDNS on. The next day however I had no internet access at all, there seemed to be a proble with openDNS, so I switched off all forwarders again, this fixed the problem.
I am just concerned that I will have problems in the future with web sites that have not yet been accessed.
The cached lookup for linear.com now has an CNAME entry but still no A entry, however linear.com seems be be resolving ok now.
I'm a bit confused as the 'exactly' how DNS resolution works, do you guys know if there is a good reference web site or book that may help my understanding and potential fault finding of any problems.
Thanks again for your help
Steve
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by: stagiraPosted on 2008-01-30 at 01:17:22ID: 20775691
Hi,
as i understand, at least one network interfaces is in client dhcp mode ? Normally these card will receive automatically the update of the Name Server change from your provider.
Have you hardly setup name server ? if yes, remove it, and let the system obtain by dhcp the DNS from BT.
Regards.