Welcome back to our series on developing your Exchange administrative skills. In this post, we’re going to talk about DNS, its importance both to Exchange and email functionality in general, and some of the specific skills budding Exchange Admins should develop. If you’re looking to become an Exchange admin, understanding not only how email systems use DNS, but also how to administer and troubleshoot DNS issues is critical. It’s not enough to know that the dependencies exist; you need to understand them intimately.
An Exchange admin doesn’t have to be a DNS admin, but he or she needs to have the same depth of understanding as a DNS admin does. It’s not enough to be able to use NSLOOKUP to check for ip.addrs, or to understand how to leverage different TTLs. While both of those skill may be required with alarming frequency, Exchange admins need to understand much more.
How DNS actually works
The first thing you want to do is get a firm grasp on the fundamentals of DNS. Since DNS is one of the fundamental underpinnings of the Internet and both a core service and a requirement for Active Directory, this will serve you well. Start here, but then be prepared to dig much deeper (see what I did there? If you did, you probably know DNS well enough to move on. If you didn’t keep going.) Once you have that down, read here for some great tips regarding name resolution. Finally, have a go at this page to get a feel for split DNS.
All the different types of records
There’s A records, CNAME records, MX records, PTR records, TXT records, and all have TTLs. MX records have weights, and you should be familiar with all of those types and what weights mean. Start by reading up here and here, though understand that there are a lot of records that no one really uses. Don’t let the full list scare you off.
There’s a very specific type of TXT record, called the SPF record, that you should get to know intimately. Our sister blog, AllSpammedUp.com, has some great coverage of SPF records. Start here, and then check out some of the follow up posts here.
Understanding how to tweak TTLs is a key component of migrating services from one system to another, or even when using DNS Round Robin records to balance services across multiple systems. There’s a great post you can read here that goes into how tweaking TTLs can benefit you.
Understanding is a great start, but you also need to know how to troubleshoot DNS when things go wrong. See this series of articles on TechNet, and then check out this video tutorial on using NSLOOKUP. These will get you started on your way. Then, bookmark this site, which is the best online set of tools for troubleshooting DNS you will ever find.
With all of the above under your belt, you should have a pretty good grasp of DNS including records, how it works, how to use it, and how to troubleshoot it.