Command line-based tools
I don't know whether I'm old school (or just old!), but it just seems easier, faster, and better to debug DNS problems from the command line. The most commonly used DNS-related diagnostic commands can be counted on to be present on most systems and, if not, they are usually easy to install using your favorite package manager, or, given the nature of DNS, you can just quickly log into another shell where you know they are installed and run your commands from there.
whois
Regardless of the issue being reported regarding any zone, the first thing I always do is a quick whois lookup for the domain (or parent domain) for the hostname involved.
The are several things I look for in the result, such as the following:
- Are we looking at the correct domain?
- Has the domain expired at the registry?
- What is the registry/registrar status of the domain?
- Is the zone even delegated to the nameservers we expect it to be?
- Is it DNSSEC-signed?
While we covered the components of a Whois record...
