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Tuesday, February 14, 2006

Why 13 DNS ?

According to famous Malaysian blogger Jeff Ooi, there are only 13 root DNS servers in this world.

The primary reason being the limitation to the datagram operated under current Internet standards and protocols. It is related to datagram size. Which means that when IPv6 is widely adopted, there will be more root servers available.

A DNS is important to resolve URL names into actual IP addresses.

Every ISP(Internet Service Provider) would have DNS and they are all mirrorring to either one of the 13 root DNS servers.

The nature of Internet Protocols prevented end-users from knowing the actuall mechanism of datagram data-communication. However, to understand DNS in a pragmatic manner without dipping one's head into the ocean of computer studies, one may want to try the following:

Whenever your Internet is down:
1. Goto the command prompt.
2. Ping for www.yahoo.com

Wait for the responses.

Positive response:

Pinging www.yahoo.akadns.net [68.142.197.79] with 32 bytes of data:

Reply from 68.142.197.79: bytes=32 time=267ms TTL=51
Reply from 68.142.197.79: bytes=32 time=264ms TTL=51
Reply from 68.142.197.79: bytes=32 time=268ms TTL=51
Reply from 68.142.197.79: bytes=32 time=268ms TTL=51

Ping statistics for 68.142.197.79:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 264ms, Maximum = 268ms, Average = 266ms

The IP address of 68.142.197.79 is the real address for Yahoo's main page's server. The DNS of the ISP has helped you to resolve the URL = www.yahoo.com into this number presentation.

Thus, should you get responses which states:

Unknown host [URL]

Then this means that the DNS is still functioning.

Wikipedia gives a good explanation of the working of DNS, even better than some books.

Accordingly, the most interesting part of the texts is regarding the explanation of delegations and zones. It is sometimes hard to explain technical processes or intelligence in laymen terms, risking being dummy.

I guess delegation is one feature for the DNS to work, by fowarding request to other DNS servers. While the concept of zones is to speed up the process of resolving URL. This is very common in the area of A.I alogorithms such as the A-Star algorithm which would dynamically define zones in order to predict the likely position of the answer.

How to know when DNS is not functioning when Internet is down?

1. Goto to command prompt.
2. PING www.yahoo.com
3. If one gets the feedback as "request time-out"
Then try to ping directly 68.142.197.79
4. If the feedback is NOT "request time-out", then the DNS is down. You maybe able to view Yahoo homepage by typing 68.142.197.79 directly to the homepage, but yet it can't save all the arses because you would still need the help of DNS for resolving other link's URL, such as mail.yahoo.com

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