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DNS problems

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by bowieb 1 view

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I'm having a problem where users in my company are getting a "page cannot be displayed" error when going to certain websites. Usually, if they refresh once or twice, the page will come up.

We are running our own DNS servers and since the currentones are a bit old, I created a new Linux DNS server using Bind 9.2.1 and pointed my desktop there. Unfortunately, this didn't affect the problem. I can recreate this behavior with both IE for Windows and Konqueror for Linux.

The only thing I've found that solves the problem is using an external DNS (Such as BellSouth's). The external DNS seems to generally run faster than mine as well.

My current DNS server is a basic Bind 9.2.1 install that is master for about 130 local domains. This particular server is only used by my internal users. What can I do to make this server work properly?

Or is there another explanation other than a screwy DNS server?

12 replies

by timwalsh

I suspect that the problem relates to the fact that your internal DNS servers can't resolve any queries for external resources they don't know about. Your DNS server must be able to forward DNS queries it cannot resolve to an external rsource.

Icould tell you how to set this up with Windows DNS, bu not Linux.

by bowieb

No, my internal servers have no problems resolving most external names. It's just that occasionally there is one that doesn't get resolved on the first try. The DNS servers know about the root servers and will query them about unknown domains. I've watched them do this using 'dig'.

by timwalsh

Is it always the same websites your users have the problems with? Does this behavior always happen when these sites are accessed?

Many times, if a website is extremely busy, you can get the error you are receiving. The fact that the website will come up eventually would support this explanation. Based on what you have said, everything appears to be working correctly at your site. Chances are good that the web server on the far end is overloaded.

The only problem with this hypothesis is tha fact that querying an external DNS server directly solves your problem.

You mention that your DNS server is master (does this mean authoritative) for 130 local domains? Are these DNS domains that you host? Your server cannot be authoritative (master?) for a DNS domain it does not host.

Your server can be authoritative (master?) only for your DNS domain (or DNS domains that you host). All other queries outside of your domain should be passed to other DNS servers without your serverattempting to resolve the query first.

by bowieb

It does seem to happen to the same websites. Generally, I get a problem the first time I hit mail.yahoo.com and www.sarc.com every day. Internal links at Yahoo also frequently fail.

I don't doubt that Yahoo is busy, but I don't thinkthey would be consistantly overloaded to the point of giving errors every day. I don't know how much traffic SARC gets.

Generally, I find that it's the same sites every day. The first time I hit them, I have to refresh at least once. After that, they are fine.

The DNS server is master for 130 domains that we host. For other domains, the server queries the root servers for info.

by pedro.v

depending on how many DNS servers you have that are able to resolve external addresses I'd like to suggest the following:

make more than one entry for the same DNS server in your DNS list

especially the compaq and hp site were very sensitive to this, since they get a large number of hits.

its related to the time-out settings I guess, the responce from the external DNS server doesn't reach your server fast enuogh to be given to the client to be able to connect.
by the time your client asks the same dns server for the ip of a site again, it has received the answer and knows where to send you to...

Its something that works fine here where we used to have a lot of problems getting to certain sites

by natem

Have you tried configuring your DNS server to forward querries to the root DNS servers? That's how my network is setup and I've never had this problem. They would be:
a.root-servers.net.
b.root-servers.net.
.......
m.root-servers.net. (last one)

by bowieb

That's the default setting for a DNS server and that's what mine have always done.

by piaconis

You mentioned that it happens when you check Yahoo and SARC first thing in the morning. Does this also happen when your users first try to access the Internet? If so, your problem may not be DNS, but rather a problem with you being able to establish the initial route. Perhaps it times out before a route or connection is established.

What are you using as your gateway to the Internet?

by bowieb

Problem was solved when I configured my DNS server to forward queries to my ISP's server rather than the root servers.

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