Dynamic Updates with Caching Only Server

Technowiz

Working on DNS and was wondering how you get DNS updates to work for clients that are in a remote location using a caching only DNS server? For example you have a branch office with a server running DHCP and DNS caching only. Do you have to somehow configure the DHCP server to update the client DNS records on your DNS server at your main office or is there a way to get the branch office clients to do this?

Mishra

I would imagine the DHCP server would look up the NS records for the zone that the branch office belongs to and update the zone accordingly.

dynamik

You can't dynamically update a caching server. A caching server only stores (caches) dns names that are requested from users/machines on the network, which makes subsequent resolutions faster (since it doesn't have to resolve the name again).

edit: I was thinking you were trying to dynamically update your clients in DNS when I saw you asking about having the DHCP server update DNS, but I don't think I understood your question. Great answer from royal.

royal

caching only means it doesn't have a zone. Therefore, when a client hits it, it will do recursion or use a forwarder or both and contact the correct dns server. The caching server will then cache the entry for a certain amount of time defined in the SOA record in the forward lookup zone. The client if pointed to the caching server will continue to use its own cache and then the server cache until both expire which can be expedited with an ipconfig /flushdns for client dns and dnscmd /clearcache for server side cache.

Technowiz

Royal,

Either you didn't understand my question or I didn't understand your answer.

I think I have a fair understanding of how a caching DNS server works. What I don't understand is how the client machines that are pointing to the caching server can update their host and if applicable pointer records on the DNS server for their domain. There is no zone for them to update on the caching server they are pointing to. So do they try to update their DNS records with the caching server which then forwards their update request to the DNS server hosting their zone at the main office? Or does it work some other way?

For example:

Where I work we have two server 2k3 domain controllers each running DNS (AD integrated) in the main office. We have another location which is currently sending all DNS queries from clients across a slow WAN link to our 2 DNS servers at the main office. If I configure a caching DNS server at the remote location how will their DNS records get updated on our 2 DNS servers in the main office when they are all pointing to the caching server? Does the caching server somehow do it for them or does it require some other special configuration?


Hope this makes it more clear than my original question.

dynamik

Ah, you had dynamic updates in the thread title. It's nice to know I'm not crazy.

http://support.microsoft.com/kb/816592 and go to An example of how DNS updates work

It looks like your client machines will query for the SOA and update with one of those servers. I'm not sure if this is exactly how it will work in your scenario though.

Technowiz

Thanks for the reply dynamik. I haven't read the entire page you sent but it looks like what I am looking for. I was thinking the client just tried to update with whatever DNS server it happened to be pointing to but it appears to be more involved than that and probably will "just work" in the scenario I gave.

Mishra

Okay it was the SOA and not the NS record. I was close. ;-p