How does the communication between a browser and a web server take place

Question

Can anyone explain how the communication takes place between the browser and web server  I want to learn how   GET  POST verbs  among others  cookies sessions query strings   work behind the scene

User · Answer

There is a commercial product with an interesting logo which lets you see all kind of traffic between server and client named charles.

Another open source tools include: Live HttpHeaders, Wireshark or Firebug.

User · Answer

Your browser is sitting on top of TCP IP  as the web is based on standards  usually port 80  what happens is when you enter an address  such as google com  your computer where the browser is running on  creates packets of data  encapsulated at each layer accordingly to the OSI standards   think of envelopes of different sizes  packed into each envelope of next size   OSI defines 7 layers  in one of the envelopes contains the source address and destination address that is the website  encoded in binary    As it reaches the 1st layer  in OSI terms  it gets transmitted across the media transmitter  such as cable  DSL     If you are connected via ISP  the layered pack of envelopes gets transmitted to the ISP  the ISP s network system  peeks through the layered pack of envelopes by decoding in reverse order to find out the address  then the ISP checks their Domain Name System database to find out if they have a route to that address  cached in memory  if it does  it forwards it across the internet network - again layered pack of envelopes     If it doesn t  the ISP interrogates the top level DNS server to say  Hey  get me the route for the address as supplied by you  ie  the browser   the top level DNS server then passes the route to the ISP which is then stored in the ISP s server memory    The layered pack of envelopes are transmitted and received by the website server after successful routing of the packets  think of routing as signposts for directions to get to the server   which in turn  unpacks the layered pack of envelopes  extracts the source address and says  Aha  that is for me  right  I know the destination address  that is you  the browser   then the server packetizes the webpages into a packed layered envelopes and sends it back  usually in reverse route  but not always the case     Your browser than receives the packetized envelopes and unpacks each of them  Then your computer descrambles the data and your browser renders the pages on the screen    I hope this answer is sufficient enough for your understanding

User · Answer

It depends on the web server  but if you re wondering what it looks like from the client side  just install Live Headers and Firebug for firefox  With the net tab in firebug and live headers open  it should be clear exactly how the two interact   For a more in-depth look at the actual data going back and forth  use wireshark

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The links for specifications of each aspect of the question is as follows    GET  POST verbs  among others  - The HTTP Specification exhaustively discusses all aspects of HTTP communication  the protocol for communication between the web server and the browser    It explains the Request message and Response message protocols  Cookies - are set by attaching a Set-Cookie HTTP Header to the HTTP response  QueryStrings - are the part of the URL in the HTTP request that follow the first occurrence of a     character   The linked specification is for section 3 4 of the URI specification  Sessions - HTTP is a synchronous  stateless protocol   Sessions  or the illusion of state  can be created by  1  using cookies to store state data as plain text on the client s computer   2  passing data-values in the URL and querystring of the request   3  submitting POST requests with a collection of values that may indicate state and   4  storing state information by a server-side persistence mechanism that is retrieved by a session-key  the session key is resolved from either the cookie  URL Querystring or POST value collection    An explanation of HTTP can go on for days  but I have attempted to provide a concise yet conceptually complete answer  and include the appropriate links for further reading of official specifications

User · Answer

this is from Browser     Server Communication

User · Answer

Communication between a browser and a webserver takes place at so many levels that is close to impossible to answer this question  HTTP plays a role  but HTTP is meaningless without TCP which is meaningless without IP which is meaningless without a physical network on which it sent  Then  there are POST vs GET requests which are similar but enough different to warrant a special dicussion  Sometimes an HTTP request needs to be authenticated  sometimes  it needs not  Mime types should be mentioned  Then  a browser sends a different request if there is a proxy  And then also encodings play a role  So  I guess  the most concise answer to this kind of question is  the browser asks the server for data and the server gives the requested data to the browser

User · Answer

Your browser first resolves the servername via DNS to an IP  Then it opens a TCP connection to the webserver and tries to communicate via HTTP  Usually that is on TCP-port 80 but you can specify a different one  http   server portnumber    HTTP looks like this   Once it is connected  it sends the request  which looks like   GET  site HTTP 1 0 Header1  bla Header2  blub  emptyline    E g   a header might be Authorization or Range  See here for more   Then the server responds like this   200 OK Header3  foo Header4  bar  content following here      E g   a header might be Date or Content-Type  See here for more   Look at Wikipedia for HTTP for some more information about this protocol

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Hyper Text Transfer Protocol  HTTP  is a protocol used for transferring web pages  like the one you re reading right now    A protocol is really nothing but a standard way of doing things  If you were to meet the President of the United States  or the king of a country  there would be specific procedures that you d have to follow  You couldn t just walk up and say  hey dude   There would be a specific way to walk  to talk  a standard greeting  and a standard way to end the conversation  Protocols in the TCP IP stack serve the same purpose   The TCP IP stack has four layers  Application  Transport  Internet  and Network  At each layer there are different protocols that are used to standardize the flow of information  and each one is a computer program  running on your computer  that s used to format the information into a packet as it s moving down the TCP IP stack  A packet is a combination of the Application Layer data  the Transport Layer header  TCP or UDP   and the IP layer header  the Network Layer takes the packet and turns it into a frame    The Application Layer     consists of all applications that use the network to transfer data  It does not care about how the data gets between two points and it knows very little about the status of the network  Applications pass data to the next layer in the TCP IP stack and then continue to perform other functions until a reply is received  The Application Layer uses host names  like www dalantech com  for addressing  Examples of application layer protocols  Hyper Text Transfer Protocol  HTTP -web browsing   Simple Mail Transfer Protocol  SMTP -electronic mail   Domain Name Services  DNS -resolving a host name to an IP address   to name just a few    The main purpose of the Application Layer is to provide a common command language and syntax between applications that are running on different operating systems -kind of like an interpreter  The data that is sent by an application that uses the network is formatted to conform to one of several set standards  The receiving computer can understand the data that is being sent even if it is running a different operating system than the sender due to the standards that all network applications conform to    The Transport Layer     is responsible for assigning source and destination port numbers to applications  Port numbers are used by the Transport Layer for addressing and they range from 1 to 65 535  Port numbers from 0 to 1023 are called  well known ports   The numbers below 256 are reserved for public  standard  services that run at the Application Layer  Here are a few  25 for SMTP  53 for DNS  udp for domain resolution and tcp for zone transfers    and 80 for HTTP  The port numbers from 256 to 1023 are assigned by the IANA to companies for the applications that they sell   Port numbers from 1024 to 65 535 are used for client side applications -the web browser you are using to read this page  for example  Windows will only assign port numbers up to 5000 -more than enough port numbers for a Windows based PC  Each application has a unique port number assigned to it by the transport layer so that as data is received by the Transport Layer it knows which application to give the data to  An example is when you have more than one browser window running  Each window is a separate instance of the program that you use to surf the web  and each one has a different port number assigned to it so you can go to www dalantech com in one browser window and this site does not load into another browser window  Applications like FireFox that use tabbed windows simply have a unique port number assigned to each tab  The Internet Layer     is the  glue  that holds networking together  It permits the sending  receiving  and routing of data   The Network Layer     consists of your Network Interface Card  NIC  and the cable connected to it  It is the physical medium that is used to transmit and receive data  The Network Layer uses Media Access Control  MAC  addresses  discussed earlier  for addressing  The MAC address is fixed at the time an interface was manufactured and cannot be changed  There are a few exceptions  like DSL routers that allow you to clone the MAC address of the NIC in your PC    For more info    Protocols TCP IP

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