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Why is DNS often joked about in the I.T. Industry?
(lemmy.world)
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this post was submitted on 13 Aug 2024
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I can speak to Windows DNS and AD.
Yes, the basis of DNS is to match IP addresses with hostnames. But there are plenty of other kinds of DNS records. SPF, DKIM, DMARC use DNS for email validation; AD uses SRV records to point clients to find domain resources. There are also reverse zones, where you send a query for an IP address to learn the hostname(s) associated with it. There are CNAME records that associate a hostname with whatever IP address another hostname is using.
Point being, there are a lot of different interconnected layers, and if some entry is wrong, it can easily have a cascading effect that creates a problem with something entirely different.
I would also extend the "It's always DNS" trope to "It's always name resolution." In a Windows environment, at least, DNS name resolution is only used when a FQDN (fully qualified domain name) is being queried. If your application is only looking for [ServerName], NetBIOS name resolution is used.
When NetBIOS name resolution is used, that is querying a WINS server (if one is specified and exists). In the absence of a WINS server, the query is sent to the "master browser" on your network segment. What machine is the "master browser"? By default, all machines on a network segment (subnet) have a browser election behind the scenes to choose the master browser, based in large part on the machines' hardware capabilities.
This means that any machine on the segment (again, by default) can become the master browser and respond to NetBIOS queries. Laptop, desktop, server, doesn't matter. There are registry entries that can be manipulated to have manual control over what machine is master browser, what machines are and are not allowed to participate in elections, but it is rare that those are configured.
Why do I know all this? Because about 25 years ago, I came across a situation where different machines were configured with different overlapping subnet masks, and users were trying to browse \\servername\share, and getting only partial results. It took a long time to narrow that down to the misconfigured subnet masks. At the company I'm currently at, the developers still use NetBIOS names instead of FQDNs in applications.
Always use FQDNs in any in-house development. Always use FQDNs when accessing resources by hostname. And if "some weird, inexplicable, possibly intermittent issue" is happening, check name resolution.