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DNS 101A crash course in the basics of website DNS, and what it takes to “go live.”
What is DNS?DNS stands for “Domain Name System.”It is one of the backbones of how theInternet works.DNS is what tells “the Internet” where toﬁnd a speciﬁc website.
DNS is like 411DNS ties an IP address to a domain name,just like 411 ties a person’s name to a phonenumber.
DNS is like 411You: “Hello, operator? Can you connect me toSeymour Butts?”Operator: “Sure, that number is 555-1234.Please hold and I’ll connect you.”
DNS is like 411You: “Hello, DNS? Can you connect me towww.seymourbutts.com?”DNS: “Sure, that IP address is 126.96.36.199.Please hold and I’ll connect you.”
How does it work?A site owner register their domain name at adomain name Registrar. (GoDaddy.Com, etc.)When they register, they are asked to assignthe domain name at least TWO NS Records,(Name Servers).ONLY the site owner or someone with accessto the Registrar can change the NS records.
NS RecordsNS Records tell “the Internet” which hostingcompany to send requests to.NS Records are provided by the hostingcompany (Rackspace, etc.)They usually look something like this:ns1.rackspace.com, ns2.rackspace.comOnce Name Servers are correct, we don’tneed to deal with the Registrar anymore.
The Website HostNow that “the Internet” knows which hostingcompany’s network to send requests to, it’sup to the hosting company’s records tonarrow it down a little.
DNS ZonesA request for seymourbutts.com is sent toRackspace because the Registrar knows theName Servers. But Rackspace hosts a LOT ofwebsites. DNS Zones tell “the Internet”where to go to ﬁnd the website once theyget to Rackspace.DNS Zones are created on the hosting webserver.
Typical RequestUser types www.seymourbutts.com into theirbrowser.DNS looks up the Name Server on record atthe registrar for www.seymourbutts.com andsends the request over to Rackspace.Rackspace then uses the DNS Zones toﬁgure out which IP address to send therequest to.
Multiple DomainsEach domain name needs its NS Recordsupdated at the Registrar.Each domain name needs its own DNS Zone.If a DNS Zone is not set up for allapplicable domains, those domains WILL NOTresolve.
Multiple DomainsBe sure to ask the client if they have morethan one domain name pointing to their site.If they do, ask whether all of the domainspoint to the website homepage.If different domains point to different pages,DNS Zones still need to be set up, butadditional programming is required.
Trouble BrewingIf the Name Servers are incorrect at theRegistrar, or if the DNS Zone is not set upcorrectly, the website WILL NOT resolveproperly.
Externally Hosted Mail MX (Mail Exchange) Records are part of the DNS Zone Record. By default, it is assumed that mail is hosted locally on the web server. If a client is hosting mail somewhere OTHER than the server hosting their website, we MUST be given correct MX information.
Externally Hosted Mail MX information is added to the DNS Zone so that their mail will continue to work. The MX information MUST come from the client’s IT Dept, or from the mail hosting company.
Externally Hosted Mail If the client’s IT department doesn’t immediately know what an MX record is, YOU ARE TALKING TO THE WRONG PERSON. Ask to speak to a representative from the company that hosts their email.
Externally Hosted Mail If the client has multiple domains AND externally hosted email, we must clarify if all domains accept email, or if they use one primary domain for email. Each additional domain that accepts email requires changes to the MX records in a DNS Zone. This takes time.
DNS Caching24-48 hours (but not really).DNS is frequently cached to speed thingsup. ISPs, corporate networks, computers andeven browsers cache DNS.DNS caching can result in delays in seeingchanges. Restarting the computer sometimeshelps.
DNS CachingA brand-new domain, or a new sub-domain(for example, http://can.seymourbutts.com)can resolve faster than NS Record changesbecause they are controlled at the hostlevel, not the Registrar. (Some hosts delayDNS updates.)Because it’s new, no cache exists for it, so itwill fetch a “live” record sooner.
DNS CachingBecause so many different things cache DNS,you may be able to see a DNS change beforethe client can - or vice versa.If DNS is not resolving properly for anyonewithin 8 hours, say something. It doesn’tusually take that long and something couldbe wrong.