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This topic is going to look at possibly the most fundamental aspects of modern networks.
DNS - Domain Name System is a naming system used for computers, services or any other resource connected to a network. The system uses a series of low and high level services to translate names and numbers. This is an application layer protocol (OSI Layer 7)
Take a list of common websites I use:
www.Tech-101.com www.BBC.co.uk www.Facebook.com
I can remember each of these incredibly easily as the site or URL (Uniform Resource Locator) is easy to remember and links the domain to the physical site I want to go to. Incredibly easy.
Now look at this:http://184.108.40.206/ http://220.127.116.11/
What are they and where do they go?
They are the numerical raw format IP addresses for Google.co.uk and an entry to bbc.co.uk. Try Google and that will work - but the bbc address won't.
A multi hosted site i.e multiple sites via a single IP will give you a mount/entry point but will not point directly to the resource.
Ok maybe we have gone full steam ahead...lets head back a bit.
So DNS will translate an IP to a host name > i.e 18.104.22.168 will translate to Google.co.uk. The basis of this is simple:Its easy to remember...I have already forgotten the 9 number I need to get to google If the resources move or change you don't need to do anything. By the times you read this the address that points to google may have changed...but www.google.co.uk will still work.
Imagine having to update every link on Tech-101 simply because the IP address changed every 2 minutes - the internet would not function as it does now. Therefore DNS helps us use names instead of number hiding the actual background logic to how the internet works.
What we combine is the ip address 22.214.171.124 and the FQDN (Fully Qualified Domain Name) eg Google.co.uk.
So how does it work?
As I mentioned DNS uses a hierarchy of top and lower level servers/domains to make up the system. By using different levels the load is spread between the servers - meaning no single server handles every request.
1 - The client will be given hints that will point it to the very root server. The root server will be the first point of contact and it will tell you where the domain server will be. I have typed in www.google.co.uk into my browser. Firstly the name google.co.uk will go through a WHOIS process - which in reality is the PC asking where is google.co.uk.
The root server will reply with an address to the name server. So it may say "Try 126.96.36.199". This will be the name server for .co.uk. This will have links to .co.uk domains (this actually happens to be a responder for OpenDNS.com)
2 - My request will then be sent to the .co.uk namespace. Google will be searched and a lower level name server found. It will say try "188.8.131.52"
3 - This request could then end at the lowest level which would return "The address is actually 184.108.40.206"
This is all fake - but the concept is correct (along with the end IP). The root level tells you how to get to the top level which directs you to the relevant intermediate steps tothe secondary or local DNS servers. The Cisco example:
Root DNS Servers: Can tell you about .com, .org, .au.si.co.uk (http://en.wikipedia.org/wiki/Root_nameserver)
Top Level Domain Servers: Can tell you about Cisco.com (http://en.wikipedia.org/wiki/Top-level_domain)
Secondary Level/Local DNS server: Can tell you about www.cisco.co.uk or mail.cisco.com
As you can see it can point me to mail servers and domain servers...the whole deal.
This is all about records - the root level servers will have a record for cisco.com - but they will not know where the resource mail.cisco.com is located. These records - used by the DNS servers all have names and specific purposes - for example an MX record (Mail Exchange Record) is used to distinguish a mail exchange for a particular host. You can read all about records here (to many form e to remember): http://en.wikipedia.org/wiki/List_of_DNS_record_types
The best way of looking at this is using the nslookup command under windows. This will translate either an ip to a hostname or hostname to ip.
1. Click Start > Run > cmd (or Start > search for cmd)
2. In the command prompt type in nslookup www.google.co.uk
This will return the server that initiated and resolved the repose (the responder) and the actual qualified address. Not all sites can be accessed using the ip returned by nslookup.
Still this gives you an idea of what is going on.
This is a simple post and will improve shortly. However it should hopefully give a good taste of what DNS is and how it has helped shape the internet as it is today.
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