As I tried to explain to a co-worker a long time ago, I firmly believe that ‘DNS is the root of all evil’. What I mean by that is that when you run into an issue accessing a network resource or experience anything strange, check DNS first. Quite often an incorrectly configured DNS server, either internal on the LAN or external at your ISP, can cause a myriad of problems. Some which are easy to resolve, and others that leave you scratching your head. I’ve detailed some of the problems and their solutions below.
- You cannot reliably access resources on your LAN. You get messages that a server or network share could not be located. Someone then innocently mentions that somebody from their ISP was in yesterday to work on the Internet. The first place you look is at the DNS servers in the TCP-IP configuration of that PC. What you find is that the tech replaced one of the DNS server entries which used to point to a DNS server on the LAN, with the address of one of the ISP’s servers. Makes the Internet come right up, and makes the user think that there is something wrong with the network.
- One morning you can access network resources, and get out to the Internet, without any issues. After lunchtime, everybody slowly but surely started to have issues. What nobody knew was that someone took down for maintenance, the only server in the network that had a DNS server running on it. An easy way to avoid this from occurring is to make sure that there are at least two DNS servers running on the network. This way if one goes down, the other will reply to DNS requests.
- Let’s say that you are on a network where the client PCs obtain their IP address configurations from a DHCP server and an existing DNS server goes down or needs to be replaced. The new server is put in place and the DHCP Server is changed to reflect the new server’s IP address, yet you continue to experience DNS issues, locating network resources. DNS address leases by default last for eight days. So, unless you reboot the PC, or perform the commands ‘ipconfig /release’ and ‘ipconfig renew’ on the PC, you will be stuck with the old settings as well as the old problem.
- One morning everyone comes into work and there are no DNS issues with locating LAN computers and resources, but some people are having issues connecting to sites on the Internet. It doesn’t happen often, but your ISP could’ve just made a change such as retiring one of their DNS servers without informing their customers that it was being replaced with a new server with a totally different IP address. Once the DNS servers are set correctly in your network firewall/router, the problem will be resolved.
- One last confounding DNS issue occurs when you are informed that nobody is receiving emails from the outside world to your in-house mail server. This could be caused by a large number of causes and could take a long time to diagnose. But someone then phones to tell you that your website appears to be down. That’s when the lightbulb goes on. The first place to check is your domains public DNS server to make sure that the MX record for your mail server and your WWW record for your website is still there. If your domain record isn’t found, then it might be something as simple and embarrassing as nobody paid the bill to maintain the DNS. Sort of like not paying the electric bill. The ISP just turned you off. Another reason could be that someone in IT logged in to make a change or addition to your domain’s DNS and accidentally may have deleted an entry or simply made a typo.
Regardless of whether or not your problem appears to be caused by a DNS error, just remember that ‘DNS is the root of all evil’, take a deep breath, and start troubleshooting right there. Or, contact us and we can help!