Packets of data to move to and fro across the internet based entirely on IP Address.  At every “network meeting point” on the internet, there is a router which examines all traffic to find out where it is headed, and then sends it to the next step.  This process is repeated at each “network meeting point” until the traffic arrives at the destination.

There is a popular utility called “Trace Route”, which will demonstrate all of the routers that a packet of data must go through to get from where you are to where it is headed.  In the following example, I ran a traceroute to http://www.google.com.

Notice the first step was a DNS lookup, converting www.google.com to 72.14.204.99. 

In true geek fashion, after 15 hops, our packet reached 1e100.net.  Google was derived from the word Googol, which is a number with 1 and 100 zeros.  Henceforth, 1e100.net stands for something to that effect.

It is important to understand that computers are binary, and therefore require input to be ultimately converted to binary.  An IPv4 address is simply 32 bits, but rather than presenting it as 11000000.10101000.00000000.00000001, humans find it more convenient to look at it like 192.168.0.1.  However, that is still a far cry from a human readable name like mail.domain.com.

This is where DNS comes into play.  DNS is a system which allows people to use names, while still providing for computers to use the numbers.  Of the many benefits of DNS, it allows you to move a domain to another IP address while keeping the domain name the same. 

Common Types of DNS Records

DNS records come in several types:

Points to a specific IP address.  “A” stands for “Address”.

Points to another record.  “CNAME” stands for “Canonical Name Record”

Specifies a domain which will handle incoming email for the domain.

Delegates a DNS zone to use the given authoritative name servers.  “NS” stands for “Name Server”.

Specifies arbitrary text associated with a name.  “TXT” stands for “Text”

DNS is a distributed system.  This means that there are thousands of DNS servers scattered around the globe.  Most internet providers will have their own DNS servers.  Most hosting providers will have their own DNS servers.  Etc…

How do they all stay in sync?  They do and they don’t!

Every DNS entry has a corresponding TTL value associated with it.  TTL means “time to live”.  This value, expressed in seconds, states how long a given DNS entry is valid before it must be refreshed from the “authoritative” DNS server for the given domain.  Typically, the TTL is set to 86,400 seconds, or 1 day.

With a TTL of 1 day, any changes to authoritative DNS records may take up to a full day (or more) to propagate around the internet.  This is worth keeping in mind before you engage in any important DNS changes.

The proper way to change DNS is to first, at least 48 hours prior to the transition period, change the TTL to a very low value (like 5 minutes).  It will still take at least a day for this to fully propagate to all relevant DNS servers.   However, once they are all aware that the TTL is 5 minutes, they will frequently check your authoritative server for updates every 5 minutes or each time a new request comes in for one of your DNS records, whichever is longer.

In other words, DNS servers only look up what they are asked to look up.  Then they retain it for the TTL period, and finally discard it (only to repeat if needed).

Every domain must be registered with a registrar.  Part of this registration information for every domain, is the DNS servers to use as “authoritative dns information” for that domain.   These NS records are transmitted to the root nameserver system. 

Every top level domain (com, net, edu, org, us, gb, br, uk, au, etc…) all have their own authoritative DNS servers.  This information is kept in the world’s root name servers, which are currently:

If you lookup the NS record for com at one of the above root servers, you will be told this:

If you lookup the NS record for appcove.com at one of the above “com” servers, you will be told this: