DNS server goes in and out

Question

I have a DNS server (Ubuntu and BIND) set up on my intranet. Most of the time it works fine but sometimes I can't get to certain subdomains. For example, in the morning foo.our.office might work but bar.our.office won't. Then, later, they'll both work. Then, later, bar.our.office and foo.our.office won't.

If I try to visit these subdomains directly on the DNS server machine, they always work. All the computers in the office are on wired connections, so I don't think it's a connectivity issue.

Any ideas as to what's going on?

Answer 1

I'm curious: could it be that I'm telling my client machine to use DNS servers A and B, A being our local DNS server and B being our ISP's DNS server? Should I just point my client machine to our local DNS server only and let our DNS server forward any requests it doesn't know what to do with?

Answer 2

Use 'dig' (linux/unix) or 'nslookup' (windows) to get real-time DNS server responses. Make sure you query the server directly. If you are going by how it looks when visiting using a browser, it is very unreliable because it can be cached and give you an impression that the server is responding when in reality it isn't. For example one might work because you visited the site yesterday, and it is still cached.

Answer 3

Look for the clients' configuration. If they are windows ones, look for the "DNS" line in the output of the command

ipconfig /all

The nslookup command in the ubuntu box looks for the nameservers listed in /etc/resolv.conf: compare the servers listed there with the ones listed by ipconfig /all.

I suggest that all the clients point to your internal DNS, that, in turn, forwards all queries it does not know (= it is not authoritative for) to some external DNS, for example those of your provider.