hello friends…many of u ask questions like how internet works.so in this article i m giving the easiest understanding of wrking of Internet using two simple examples…
example 1 – what happens when u type a domain abc.com in ur browser.
example 2 - what happens when u send mail at user@example.com
Example 1:
Now u JUST don’t type abc.com in ur browser do u ? see a simple most common step u do do is Connect Internet !!!
it looks common BUT it is imp…as when u connect to internet (generally)
u get the IP of the DNS resolvers nameservers.Now u got 2 nameservers which will resolve name abc.com for u to an IP
so now u can type abc.com …:)
now as u type,a DNS query is generated.
DNS query-its AIM is here to resolve abc.com to *.*.*.* IP where * is from 0 to 255
Root of DNS query:
1.it goes to nameservers of ur ISP to ask the IP of abc.com….
Now ur ISP can give two answers a)i know the IP as it is in my cache.
b)i don’t know
NOW “i don’t know” here means that it is not in cache BUT as ur ISP namservers know the IP of 13 defined Root Nameservers so it will forward ur dns query to anyone of Root Nameserver depending upon which is near and many other factors.
2.now ur dns query as Root Nameservers about abc.com root nameservers say-keep EVERYTHING on one side and tell me what is last so here it is com (from abc.com)
now they again forward dns query to Generic TLD servers i.e which know about the Authoritative Nameservers of any .com,.biz,.net and .org
3.so now ur query is at Generic Servers.there it asks for the IP of abc.com….they say “i don’t know about abc.com’s IP but i have it as an sub-zone under com and i m having its nameservers as NS and u may go there”
so Generic servers return Nameservers as well as their IP (Glue records) to the dns query.
4.so the dns query is forwarded to other nameservers (which are GENERALLY Authoritative DNS servers of the domain).now it asks for abc.com to it.
it can return these answers:
a)i know the IP as an A record…->end of quiry as IP of abc.com hd been returned
b)i don’t know IP but i have its NS records pointing to any other (may be) authoritative servers.so now query further routes and this go on untill query ends ….i.e get A records or show up DNS error.
c)it may say abc.com is an alias of another domain xyz.com i.e abc.com->cname to xyz.com hence now query goes for xyz.com….and returns the IP of xyz.com
d)i don’t know !!! yes d) is an result of DNS misconfiguration.hence we get IP for abc.com thus enabling our system to start transferring data using TCP as protocol.
Example 2
what happens when u send mail at user@abc.com
here again a DNS query is generated BUT from smtp servers of the email provider.
its AIM is to resolve abc.com and get the MX or Apex A record…(only in case MX is absent)
1.ur smpt server will resolve abc.com as per the same pattern as described in above example 1
2.finally when the DNS query (generated by the smtp servers) reaches the Authoritative nameservers of abc.com it asks there for MX record as per the priority they r returned.
now e.g if it returns MX as mx1.hostedmail.emailhost.com then this emailhost.com is further resolved and so on until the email provider gets the IP of receiving servers.
after getting IP of recieving servers the sender’s mails servers transfers the data following SMTP as protocol.