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DNS Domain Name System

You likely use DNS servers without realizing it. DNS stands for domain name servers. Domain name servers are very important for using the internet and they are fascinating. The DNS system is one of the largest and most active distributed databases in the world. If there was no DNS, there would be no internet!

Everytime you surf the internet or send an email, you are using the DNS system. Its main function is to translate between domain names and IP addresses and to list the mail-exchange servers accepting e-mail for each domain. A frequently used analogy to explain DNS is that it serves as the "phone book" for the Internet by translating human-friendly computer host names into IP addresses. For instance, www.uptrends.com translates to 208.77.188.166.

DNS servers translate domain names to IP addresses.

DNS servers translate domain names to IP addresses. This sounds very easy, and most of the time it is. However when you read the five points below you will understand some of the complexities involved:

On the internet there are billions of IP addresses used
Every day new domain names are created
Every day, domain names and IP addresses will change
Billions of DNS requests are made every day. When you are on the internet you will probably make a hundred or more DNS requests per day.
Millions of people work to change and add domain names and IP addresses every day.

No other database in the world will get as many requests as the DNS system. Just imagine what it would be like without it! If we had to remember the IP addresses of each website while we were surfing the internet, the internet would never have become as popular as it is. Clearly, remember a word or phrase is considerably easier than remembering an IP address. For example, it is much easier to remember the domain Uptrends.com than the IP address 208.77.188.166. So, DNS servers make it much easier for you to surf the internet.

DNS servers continually do two things:

They accept requests from programs to convert domain names into IP addresses.
They accept requests from other name servers to convert domain names into IP addresses.

When a request comes in, the name server can do one of four things with it:

It can answer the request with an IP address because it already knows the IP address for the domain.
It can contact another name server and try to find the IP address for the name requested. It may have to do this multiple times.
It can say, "I don't know the IP address for the domain you requested, but here's the IP address for a name server that knows more than I do."
It can return an error message because the requested domain name is invalid or does not exist.

When you type a URL into your browser, the browser will first convert the domain name and host name into an IP address. This allows the browser to request a webpage from the machine that answers that IP address. The browser gets the IP address by having a conversation with a name server.

For example, if you type "www.uptrends.com" into your browser, the browser needs to convert that URL into an IP address. The browser will hand "www.uptrends.com" to its default name server and ask it to convert it.

The name server may already know the IP address for www.uptrends.com. That would be the case if another request to resolve www.uptrends.com came in recently (name servers cache IP addresses to speed things up). When this happens, the name server will return the IP address immediately. Let's assume, however, that the name server has to start from scratch.

A name server would start its search for an IP address by contacting something called a root name servers. The root servers know the IP address for all of the other name servers. When your name server needs to get the IP address for www.uptrends.com, it would ask the root for help. The root might then say "I don't know the IP address for www.uptrends.com, but here's the IP address for the COM name server." Here are two important points to remember about root servers:

There are many of them scattered all over the planet.
Every name server has a list of all of the known root servers. It contacts the first root server in the list, and if that doesn't work it contacts the next one in the list, and so on.

The DNS root server

The root server knows the IP addresses of the name servers handling hundreds of top-level domains. It provides your name server the IP address for a name server for the COM domain. Your name server then sends a query to the COM name server asking it if it knows the IP address for www.uptrends.com. The name server for the COM domain knows the IP addresses for the name servers handling the uptrends.com domain, so it returns those. Your name server then contacts the name server for uptrends.com and asks if it knows the IP address for www.uptrends.com. It does, so it returns the IP address to your name server, which returns it to the browser, which can then contact the server for www.uptrends.com to get a Web page.

Redundancy and caching is important for the domain name system

One of the keys to making this work is redundancy. There are multiple name servers at every level, so if one fails, there are others to handle the requests. There are, for example, three different machines running name servers for uptrends.com requests. All three would have to fail for there to be a problem.

The other key is caching. Once a name server resolves a request, it caches all of the IP addresses it receives. Once it has made a request to a root server for any COM domain, it knows the IP address and no longer needs to bug the root servers again for that information. Name servers can do this for every request, and this caching helps to keep things from bogging down.

Name servers do not cache forever, though. The caching has a component, called the Time To Live (TTL), that controls how long a server will cache a piece of information. When the server receives an IP address, it receives the TTL with it. The name server will cache the IP address for that period of time (ranging from minutes to days) and then discard it. The TTL allows changes in name servers to propagate. Not all name servers respect the TTL they receive, however. When Uptrends moved its machines over to new servers, it took three weeks for the transition to propagate throughout the Web. We put a little tag that said "new server" in the upper left corner of the home page so people could tell whether they were seeing the new or the old server during the transition.

What you can do with the Uptrends DNS monitoring service

The most common item you may wish to verify is whether your domain name (www.uptrends.com) is still pointing to the IP address of your web server. Your provider’s name server is the primary, first-hand source of this information. By monitoring this DNS query directly, we will detect any DNS problems, even before your website becomes unavailable for your visitors and customers.

Uptrends' DNS probe lets you do extensive DNS health checks, including: verify your website domain names (A and CNAME records), mail server domain name mappings (MX records), DNS zone delegates (NS records), authoritative information about DNS zones (SOA records) and other DNS information, contained in TXT records (including SPF information for e-mail authentication).

Uptrends’ external DNS monitoring service helps you monitor, diagnose, receive notifications and access reports regarding the performance of your DNS servers. We have monitoring stations all over the world to ensure data reliability.

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Uptrends continues to serve as a leading provider of DNS monitoring services for over 1500 customers in 23 countries. And because we have offices in both the US and Europe, you are guaranteed around the clock, responsive customer support. Signup for a free trial account now!

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