What is the difference between a port and a socket

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This was a question raised by one of the software engineers in my organisation   I m interested in the broadest definition

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A connection socket  fd  is presented for local address   local port   peer address   peer port  Process recv send data via socket abstract  A listening socket  fd  is presented for local address   local listening port  Process can accept new connection via socket

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They are terms from two different domains   port  is a concept from TCP IP networking   socket  is an API  programming  thing  A  socket  is made  in code  by taking a port and a hostname or network adapter and combining them into a data structure that you can use to send or receive data

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Generally  you will get a lot of theoretical but one of the easiest ways to differentiate these two concepts is as follows   In order to get a service  you need a service number  This service number is called a port  Simple as that   For example  the HTTP as a service is running on port 80   Now  many people can request the service and a connection from client-server has established  There will be a lot of connections  Each connection represent a client  In order to maintain each connection  the server creates a socket per connection to maintain its client

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Short brief answer   A port can be described as an internal address within a host that identifies a program or process   A socket can be described as a programming interface allowing a program to communicate with other programs or processes  on the internet  or locally

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With some analogy  Although a lot technical stuff is already given above for sockets    I would like to add my answer  just in case   if somebody still could not feel the difference between ip  port and sockets  Consider a server S   and say person X Y Z need a service  say chat service  from that server S  then   IP address tells --  who  is that chat server  S  that X Y Z  want to contact  okay  you got  who is the server   but suppose that server  S  is providing some other services to other people as well say  S  provides storage services to person A B C  then  port tells ---  which  service you  X Y Z  need i e  chat service and not that storage service  okay    you make server to come to know that  chat service  is what you want and not the storage  but   you are three and the server might want to identify all the three differently  there comes the socket  now socket tells--  which one  particular connection  that is   say    socket 1 for person X  socket 2 for person Y  and socket 3 for person Z  I hope it helps someone who was still confused

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from Oracle Java Tutorial      A socket is one endpoint of a two-way communication link between two programs running on the network  A socket is bound to a port number so that the TCP layer can identify the application that data is destined to be sent to

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A single port can have one or more sockets connected with different external IP s like a multiple electrical outlet     TCP    192 168 100 2 9001     155 94 246 179 39255   ESTABLISHED     1312   TCP    192 168 100 2 9001     171 25 193 9 61832     ESTABLISHED     1312   TCP    192 168 100 2 9001     178 62 199 226 37912   ESTABLISHED     1312   TCP    192 168 100 2 9001     188 193 64 150 40900   ESTABLISHED     1312   TCP    192 168 100 2 9001     198 23 194 149 43970   ESTABLISHED     1312   TCP    192 168 100 2 9001     198 49 73 11 38842     ESTABLISHED     1312

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A socket is basically an endpoint for network communication  consisting of at least an IP-address and a port  In Java C  a socket is a higher level implementation of one side of a two-way connection   Also  a definition in the Java documentation

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A socket consists of three things    An IP address A transport protocol A port number   A port is a number between 1 and 65535 inclusive that signifies a logical gate in a device  Every connection between a client and server requires a unique socket   For example    1030 is a port   10 1 1 2   TCP   port 1030  is a socket

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A socket is a structure in your software   It s more-or-less a file  it has operations like read and write   It isn t a physical thing  it s a way for your software to refer to physical things   A port is a device-like thing   Each host has one or more networks  those are physical   a host has an address on each network   Each address can have thousands of ports    One socket only may be using a port at an address   The socket allocates the port approximately like allocating a device for file system I O   Once the port is allocated  no other socket can connect to that port   The port will be freed when the socket is closed   Take a look at TCP IP Terminology

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An application consists of pair of processes which communicate over the network  client-server pair   These processes send and receive messages  into and from the network through a software interface called socket  Considering the analogy presented in the book  Computer Networking  Top Down Approach   There is a house that wants to communicate with other house  Here  house is analogous to a process  and door to a socket  Sending process assumes that there is a infrastructure on the other side of the door that will transport the data to the destination  Once the message is arrived on the other side  it passes through receiver s door  socket  into the house  process   This illustration from the same book can help you   Sockets are part of transport layer  which provides logical communication to applications  This means that from application s point of view both hosts are directly connected to each other  even though there are numerous routers and or switches between them  Thus a socket is not a connection itself  it s the end point of the connection  Transport layer protocols are implemented only on hosts  and not on intermediate routers  Ports provide means of internal addressing to a machine  The primary purpose it to allow multiple processes to send and receive data over the network without interfering with other processes  their data   All sockets are provided with a port number  When a segment arrives to a host  the transport layer examines the destination port number of the segment  It then forwards the segment to the corresponding socket  This job of delivering the data in a transport layer segment to the correct socket is called de-multiplexing  The segment s data is then forwarded to the process attached to the socket

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A socket   IP Address   a port  numeric address  Together they identify an end-point for a network connection on a machine   Did I just flunk network 101

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A socket address is an IP address  amp  port number 123 132 213 231           IP address                 1234      port number 123 132 213 231 1234      socket address  A connection occurs when 2 sockets are bound together

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A port denotes a communication endpoint in the TCP and UDP transports for the IP network protocol  A socket is a software abstraction for a communication endpoint commonly used in implementations of these protocols  socket API   An alternative implementation is the XTI TLI API   See also   Stevens  W  R  1998  UNIX Network Programming  Networking APIs  Sockets and XTI  Volume 1  Prentice Hall  Stevens  W  R   1994  TCP IP Illustrated  Volume 1  The Protocols  Addison-Wesley

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A socket is a special type of file handle which is used by a process to request network services from the operating system  A socket address is the triple   protocol  local-address  local-process  where the local process is identified by a port number   In the TCP IP suite  for example    tcp  193 44 234 3  12345   A conversation is the communication link between two processes thus depicting an association between two  An association is the 5-tuple that completely specifies the two processes that comprise a connection   protocol  local-address  local-process  foreign-address  foreign-process   In the TCP IP suite  for example    tcp  193 44 234 3  1500  193 44 234 5  21   could be a valid association   A half-association is either   protocol  local-address  local-process   or   protocol  foreign-address  foreign-process   which specify each half of a connection   The half-association is also called a socket or a transport address  That is  a socket is an end point for communication that can be named and addressed in a network  The socket interface is one of several application programming interfaces  APIs  to the communication protocols  Designed to be a generic communication programming interface  it was first introduced by the 4 2BSD UNIX system  Although it has not been standardized  it has become a de facto industry standard

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Port and socket can be compared to the Bank Branch       The building number of the  Bank  is analogous to IP address  A bank has got different sections like    Savings account department Personal loan department Home loan department Grievance department   So 1  savings account department   2  personal loan department   3  home loan department  and 4  grievance department  are ports   Now let us say you go to open a savings account  you go to the bank  IP address   then you go to  savings account department   port number 1   then you meet one of the employees working under  savings account department   Let us call him SAVINGACCOUNT EMPLOYEE1 for opening account   SAVINGACCOUNT EMPLOYEE1 is your socket descriptor  so there may be  SAVINGACCOUNT EMPLOYEE1 to SAVINGACCOUNT EMPLOYEEN  These are all socket descriptors   Likewise  other departments will be having employess working under them and they are analogous to socket

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Firsty  I think we should start with a little understanding of what constitutes getting a packet from A to B   A common definition for a network is the use of the OSI Model which separates a network out into a number of layers according to purpose  There are a few important ones  which we ll cover here    The data link layer  This layer is responsible for getting packets of data from one network device to another and is just above the layer that actually does the transmitting  It talks about MAC addresses and knows how to find hosts based on their MAC  hardware  address  but nothing more  The network layer is the layer that allows you to transport data across machines and over physical boundaries  such as physical devices  The network layer must essentially support an additional address based mechanism which relates somehow to the physical address  enter the Internet Protocol  IPv4   An IP address can get your packet from A to B over the internet  but knows nothing about how to traverse individual hops  This is handled by the layer above in accordance with routing information  The transport layer  This layer is responsible for defining the way information gets from A to B and any restrictions  checks or errors on that behaviour  For example  TCP adds additional information to a packet such that it is possible to deduce if packets have been lost    TCP contains  amongst other things  the concept of ports  These are effectively different data endpoints on the same IP address to which an Internet Socket  AF INET  can bind    As it happens  so too does UDP  and other transport layer protocols  They don t technically need to feature ports  but these ports do provide a way for multiple applications in the layers above to use the same computer to receive  and indeed make  outgoing connections   Which brings us to the anatomy of a TCP or UDP connection  Each features a source port and address  and a target port and address  This is so that in any given session  the target application can respond  as well as receive  from the source   So ports are essentially a specification-mandated way of allowing multiple concurrent connections sharing the same address   Now  we need to take a look at how you communicate from an application point of view to the outside world  To do this  you need to kindly ask your operating system and since most OSes support the Berkeley Sockets way of doing things  we see we can create sockets involving ports from an application like this   int fd   socket AF INET  SOCK STREAM  0      tcp socket int fd   socket AF INET  SOCK DGRAM  0      udp socket    later we bind      Great  So in the sockaddr structures  we ll specify our port and bam  Job done  Well  almost  except   int fd   socket AF UNIX  SOCK STREAM  0     is also possible  Urgh  that s thrown a spanner in the works   Ok  well actually it hasn t  All we need to do is come up with some appropriate definitions    An internet socket is the combination of an IP address  a protocol and its associated port number on which a service may provide data  So tcp port 80  stackoverflow com is an internet socket   An unix socket is an IPC endpoint represented in the file system  e g   var run database sock  A socket API is a method of requesting an application be able to read and write data to a socket    Voila  That tidies things up  So in our scheme then     A port is a numeric identifier which  as part of a transport layer protocol  identifies the service number which should respond to the given request    So really a port is a subset of the requirements for forming an internet socket  Unfortunately  it just so happens that the meaning of the word socket has been applied to several different ideas  So I heartily advise you name your next project socket  just to add to the confusion

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There seems to be a lot of answers equating socket with the connection between 2 PC s  which I think is absolutely incorrect  A socket has always been the endpoint on 1 PC  that may or may not be connected - surely we ve all used listener or UDP sockets  at some point  The important part is that it s addressable and active  Sending a message to 1 1 1 1 1234 is not likely to work  as there is no socket defined for that endpoint   Sockets are protocol specific - so the implementation of uniqueness that both TCP IP and UDP IP uses   ipaddress port   is different than eg   IPX  Network  Node  and   ahem  socket - but a different socket than is meant by the general  socket  term  IPX socket numbers are equivalent to IP ports   But  they all offer a unique addressable endpoint   Since IP has become the dominant protocol  a port  in networking terms  has become synonomous with either a UDP or TCP port number - which is a portion of the socket address    UDP is connection-less - meaning no virtual circuit between the 2 endpoints is ever created  However  we still refer to UDP sockets as the endpoint  The API functions make it clear that both are just different type of sockets - SOCK DGRAM is UDP  just sending a message  and SOCK STREAM is TCP  creating a virtual circuit   Technically  the IP header  holds the IP Address  and the protocol on top of IP  UDP or TCP  holds the port number  This makes it possible to have other protocols  eg  ICMP that have no port numbers  but do have IP addressing information

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Socket is an abstraction provided by kernel to user applications for data I O  A socket type is defined by the protocol its handling  an IPC communication etc  So if somebody creates a TCP socket he can do manipulations like reading data to socket and writing data to it by simple methods and the lower level protocol handling like TCP conversions and forwarding packets to lower level network protocols is done by the particular socket implementation in the kernel  The advantage is that user need not worry about handling protocol specific nitigrities and should just read and write data to socket like a normal buffer  Same is true in case of IPC  user just reads and writes data to socket and kernel handles all lower level details based on the type of socket created   Port together with IP is like providing an address to the socket  though its not necessary  but it helps in network communications

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As simply as possible  there s no physical difference  between a socket and a port  the way there is between  e g   PATA and SATA   They re just bits of software reading and writing a NIC   A port is essentially a public socket  some of which are well-known well-accepted  the usual example being 80  dedicated to HTTP   Anyone who wants to exchange traffic using a certain protocol  HTTP in this instance  canonically goes to port 80   Of course  80 is not physically dedicated to HTTP  it s not physically anything  it s just a number  a logical value   and could be used on some particular machine for some other protocol ad libitum  as long as those attempting to connect know which protocol  which could be quite private  to use   A socket is essentially a private port  established for particular purposes known to the connecting parties but not necessarily known to anyone else   The underlying transport layer is usually TCP or UDP  but it doesn t have to be   The essential characteristic is that both ends know what s going on  whatever that might be   The key here is that when a connection request is received on some port  the reply handshake includes information about the socket created to service the particular requester   Subsequent communication takes place through that  private  socket connection  not the public port connection on which the service continues to listen for connection requests

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Port   A port can refer to a physical connection point  for peripheral devices such as serial  parallel  and USB ports   The term port also refers to certain Ethernet connection points  s uch as those on a hub  switch  or router    Socket   A socket represents a single connection between two network applications   These two applications nominally run on different computers   but sockets can also be used for interprocess communication on a single computer   Applications can create multiple sockets for communicating with each other   Sockets are bidirectional  meaning that either side of the connection is capable of both sending and receiving data

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A socket allows to the communication between two applications in a single  machine or two machine  actually it is like door  if the door opens there can  be a connection between the process or application that are inside the door  and outside the door    There are 4 types of sockets    stream sockets datagram sockets raw sockets sequential packet sockets    Sockets are mostly used in client-server applications  The port identifies different end points on a network address  It contains a numerical value    As overall a socket is a combination of a port and a network address

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The port was the easiest part  it is just a unique identifier for a socket  A socket is something processes can use to establish connections and to communicate with each other  Tall Jeff had a great telephone analogy which was not perfect  so I decided to fix it    ip and port   phone number socket   phone device connection   phone call establishing connection   calling a number processes  remote applications   people messages   speech

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These are basic networking concepts so I will explain them in an easy yet a comprehensive way to understand in details    A socket is like a telephone  i e  end to end device for communication  IP is like your telephone number  i e  address for your socket  Port is like the person you want to talk to  i e  the service you want to order from that address  A socket can be a client or a server socket  i e  in a company the telephone of the customer support is a server but a telephone in your home is mostly a client    So a socket in networking is a virtual communication device bound to a pair  ip   port     address   service     Note     A machine  a computer  a host  a mobile  or a PC can have multiple addresses   multiple open ports  and thus multiple sockets  Like in an office you can have multiple telephones with multiple telephone numbers and multiple people to talk to   Existence of an open active port necessitate that you must have a socket bound to it  because it is the socket that makes the port accessible  However  you may have unused ports for the time being  Also note  in a server socket you can bind it to  a port  a specific address of a machine  or to  a port  all addresses of a machine  as in the telephone you may  connect many telephone lines  telephone numbers  to a telephone or one specific telephone line to a telephone and still you can reach a person through all these telephone lines or through a specific telephone line  You can not associate  bind  a socket with two ports as in the telephone usually you can not always have two people using the same telephone at the same time   Advanced  on the same machine you cannot have two sockets with same type  client  or server  and same port and ip  However  if you are a client you can open two connections  with two sockets  to a server because the local port in each of these client s sockets  is different    Hope it clears you doubts

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In a broad sense  Socket - is just that  a socket  just like your electrical  cable or telephone socket  A point where  requisite stuff   power  signal  information  can go out and come in from  It hides a lot of detailed stuff  which is not required for the use of the  requisite stuff   In software parlance  it provides a generic way of defining a mechanism of communication between two entities  those entities could be anything - two applications  two physically separate devices  User  amp  Kernel space within an OS  etc   A Port is an endpoint discriminator  It differentiates one endpoint from another  At networking level  it differentiates one application from another  so that the networking stack can pass on information to the appropriate application

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Relative TCP IP terminology which is what I assume is implied by the question  In layman s terms   A PORT is like the telephone number of a particular house in a particular zip code  The ZIP code of the town could be thought of as the IP address of the town and all the houses in that town   A SOCKET on the other hand is more like an established phone call between telephones of a pair of houses talking to each other  Those calls can be established between houses in the same town or two houses in different towns  It s that temporary established pathway between the pair of phones talking to each other that is the SOCKET

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In a broad sense  Socket - is just that  a socket  just like your electrical  cable or telephone socket  A point where  requisite stuff   power  signal  information  can go out and come in from  It hides a lot of detailed stuff  which is not required for the use of the  requisite stuff   In software parlance  it provides a generic way of defining a mechanism of communication between two entities  those entities could be anything - two applications  two physically separate devices  User  amp  Kernel space within an OS  etc   A Port is an endpoint discriminator  It differentiates one endpoint from another  At networking level  it differentiates one application from another  so that the networking stack can pass on information to the appropriate application

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A socket represents a single connection between two network applications  These two applications nominally run on different computers  but sockets can also be used for interprocess communication on a single computer  Applications can create multiple sockets for communicating with each other  Sockets are bidirectional  meaning that either side of the connection is capable of both sending and receiving data  Therefore a socket can be created theoretically at any level of the OSI model from 2 upwards  Programmers often use sockets in network programming  albeit indirectly  Programming libraries like Winsock hide many of the low-level details of socket programming  Sockets have been in widespread use since the early 1980s   A port represents an endpoint or  channel  for network communications  Port numbers allow different applications on the same computer to utilize network resources without interfering with each other  Port numbers most commonly appear in network programming  particularly socket programming  Sometimes  though  port numbers are made visible to the casual user  For example  some Web sites a person visits on the Internet use a URL like the following   http   www mairie-metz fr 8080  In this example  the number 8080 refers to the port number used by the Web browser to connect to the Web server  Normally  a Web site uses port number 80 and this number need not be included with the URL  although it can be    In IP networking  port numbers can theoretically range from 0 to 65535  Most popular network applications  though  use port numbers at the low end of the range  such as 80 for HTTP    Note  The term port also refers to several other aspects of network technology  A port can refer to a physical connection point for peripheral devices such as serial  parallel  and USB ports  The term port also refers to certain Ethernet connection points  such as those on a hub  switch  or router   ref http   compnetworking about com od basicnetworkingconcepts l bldef port htm  ref http   compnetworking about com od itinformationtechnology l bldef socket htm

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A port is an entity that is used by networking protocols to attain access to connected hosts  Ports could be application-specific or related to a certain communication medium  Different protocols use different ports to access the hosts  like HTTP uses port 80 or FTP uses port 23  You can assign user-defined port numbers in your application  but they should be above 1023    Ports open up the connection to the required host while sockets are an endpoint in an inter-network or an inter-process communication  Sockets are assigned by APIs Application Programming Interface  by the system    A more subtle difference can be made saying that  when a system is rebooted ports will be present while the sockets will be destroyed

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Already theoretical answers have been given to this question  I would like to give a practical example to this question  which will clear your understanding about Socket and Port   I found it here     This example will walk you thru the process of connecting to a website  such as Wiley  You would open your web browser  like Mozilla Firefox  and type www wiley com into the address bar  Your web browser uses a Domain Name System  DNS  server to look up the name www wiley com to identify its IP address is  For this example  the address is 192 0 2 100       Firefox makes a connection to the 192 0 2 100 address and to the port   where the application layer web server is operating  Firefox knows   what port to expect because it is a well-known port   The well-known   port for a web server is TCP port 80       The destination socket that Firefox attempts to connect is written as   socket port  or in this example  192 0 2 100 80  This is the server   side of the connect  but the server needs to know where to send the   web page you want to view in Mozilla Firefox  so you have a socket for   the client side of the connection also       The client side connection is made up of your IP address  such as   192 168 1 25  and a randomly chosen dynamic port number  The socket associated with Firefox looks like 192 168 1 25 49175  Because web   servers operate on TCP port 80  both of these sockets are TCP sockets    whereas if you were connecting to a server operating on a UDP port    both the server and client sockets would be UDP sockets

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A socket is a communication endpoint  A socket is not directly related to the TCP IP protocol family  it can be used with any protocol your system supports  The C socket API expects you to first get a blank socket object from the system that you can then either bind to a local socket address  to directly retrieve incoming traffic for connection-less protocols or to accept incoming connection requests for connection-oriented protocols  or that you can connect to a remote socket address  for either kind of protocol   You can even do both if you want to control both  the local socket address a socket is bound to and the remote socket address a socket is connected to  For connection-less protocols connecting a socket is even optional but if you don t do that  you ll have to also pass the destination address with every packet you want to send over the socket as how else would the socket know where to send this data to  Advantage is that you can use a single socket to send packets to different socket addresses  Once you have your socket configured and maybe even connected  consider it to be a bi-directional communication pipe  You can use it to pass data to some destination and some destination can use it to pass data back to you  What you write to a socket is send out and what has been received is available for reading   Ports on the other hand are something that only certain protocols of the TCP IP protocol stack have  TCP and UDP packets have ports  A port is just a simple number  The combination of source port and destination port identify a communication channel between two hosts  E g  you may have a server that shall be both  a simple HTTP server and a simple FTP server  If now a packet arrives for the address of that server  how would it know if that is a packet for the HTTP or the FTP server  Well  it will know so as the HTTP server will run on port 80 and the FTP server on port 21  so if the packet arrives with a destination port 80  it is for the HTTP server and not for the FTP server  Also the packet has a source port since without such a source port  a server could only have one connection to one IP address at a time  The source port makes it possible for a server to distinguish otherwise identical connections  they all have the same destination port  e g  port 80  the same destination IP  the IP of the server   and the same source IP  as they all come from the same client  but as they have a different source ports  the server can distinguish them from each other  And when the server sends back replies  it will do so to the port the request came from  that way the client can also distinguish different replies it receives from the same server

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Summary A TCP socket is an endpoint instance defined by an IP address and a port in the context of either a particular TCP connection or the listening state  A port is a virtualisation identifier defining a service endpoint  as distinct from a service instance endpoint aka session identifier   A TCP socket is not a connection  it is the endpoint of a specific connection  There can be concurrent connections to a service endpoint  because a connection is identified by both its local and remote endpoints  allowing traffic to be routed to a specific service instance  There can only be one listener socket for a given address port combination  Exposition This was an interesting question that forced me to re-examine a number of things I thought I knew inside out  You d think a name like  quot socket quot  would be self-explanatory  it was obviously chosen to evoke imagery of the endpoint into which you plug a network cable  there being strong functional parallels  Nevertheless  in network parlance the word  quot socket quot  carries so much baggage that a careful re-examination is necessary  In the broadest possible sense  a port is a point of ingress or egress  Although not used in a networking context  the French word porte literally means door or gateway  further emphasising the fact that ports are transportation endpoints whether you ship data or big steel containers  For the purpose of this discussion I will limit consideration to the context of TCP-IP networks  The OSI model is all very well but has never been completely implemented  much less widely deployed in high-traffic high-stress conditions  The combination of an IP address and a port is strictly known as an endpoint and is sometimes called a socket  This usage originates with RFC793  the original TCP specification  A TCP connection is defined by two endpoints aka sockets  An endpoint  socket  is defined by the combination of a network address and a port identifier  Note that address port does not completely identify a socket  more on this later   The purpose of ports is to differentiate multiple endpoints on a given network address  You could say that a port is a virtualised endpoint  This virtualisation makes multiple concurrent connections on a single network interface possible   It is the socket pair  the 4-tuple consisting of the client IP address  client port number  server IP address  and server port number  that specifies the two endpoints that uniquely identifies each TCP connection in an internet   TCP-IP Illustrated Volume 1  W  Richard Stevens   In most C-derived languages  TCP connections are established and manipulated using methods on an instance of a Socket class  Although it is common to operate on a higher level of abstraction  typically an instance of a NetworkStream class  this generally exposes a reference to a socket object  To the coder this socket object appears to represent the connection because the connection is created and manipulated using methods of the socket object  In C   to establish a TCP connection  to an existing listener  first you create a TcpClient  If you don t specify an endpoint to the TcpClient constructor it uses defaults - one way or another the local endpoint is defined  Then you invoke the Connect method on the instance you ve created  This method requires a parameter describing the other endpoint  All this is a bit confusing and leads you to believe that a socket is a connection  which is bollocks  I was labouring under this misapprehension until Richard Dorman asked the question  Having done a lot of reading and thinking  I m now convinced that it would make a lot more sense to have a class TcpConnection with a constructor that takes two arguments  LocalEndpoint and RemoteEndpoint  You could probably support a single argument RemoteEndpoint when defaults are acceptable for the local endpoint  This is ambiguous on multihomed computers  but the ambiguity can be resolved using the routing table by selecting the interface with the shortest route to the remote endpoint  Clarity would be enhanced in other respects  too  A socket is not identified by the combination of IP address and port        TCP demultiplexes incoming segments using all four values that comprise the local and foreign addresses  destination IP address  destination port number  source IP address  and source port number  TCP cannot determine which process gets an incoming segment by looking at the destination port only  Also  the only one of the  various  endpoints at  a given port number  that will receive incoming connection requests is the one in the listen state   p255  TCP-IP Illustrated Volume 1  W  Richard Stevens   As you can see  it is not just possible but quite likely for a network service to have numerous sockets with the same address port  but only one listener socket on a particular address port combination  Typical library implementations present a socket class  an instance of which is used to create and manage a connection  This is extremely unfortunate  since it causes confusion and has lead to widespread conflation of the two concepts  Hagrawal doesn t believe me  see comments  so here s a real sample  I connected a web browser to http   dilbert com and then ran netstat -an -p tcp  The last six lines of the output contain two examples of the fact that address and port are not enough to uniquely identify a socket  There are two distinct connections between 192 168 1 3  my workstation  and 54 252 94 236 80  the remote HTTP server    TCP    192 168 1 3 63240      54 252 94 236 80       SYN SENT   TCP    192 168 1 3 63241      54 252 94 236 80       SYN SENT   TCP    192 168 1 3 63242      207 38 110 62 80       SYN SENT   TCP    192 168 1 3 63243      207 38 110 62 80       SYN SENT   TCP    192 168 1 3 64161      65 54 225 168 443      ESTABLISHED  Since a socket is the endpoint of a connection  there are two sockets with the address port combination 207 38 110 62 80 and two more with the address port combination 54 252 94 236 80  I think Hagrawal s misunderstanding arises from my very careful use of the word  quot identifies quot   I mean  quot completely  unambiguously and uniquely identifies quot   In the above sample there are two endpoints with the address port combination 54 252 94 236 80  If all you have is address and port  you don t have enough information to tell these sockets apart  It s not enough information to identify a socket  Addendum Paragraph two of section 2 7 of RFC793 says  A connection is fully specified by the pair of sockets at the ends   A local socket may participate in many connections to different foreign sockets   This definition of socket is not helpful from a programming perspective because it is not the same as a socket object  which is the endpoint of a particular connection  To a programmer  and most of this question s audience are programmers  this is a vital functional difference   plugwash makes a salient observation   The fundamental problem is that the TCP RFC definition of socket is in conflict with the defintion of socket used by all major operating systems and libraries   By definition the RFC is correct  When a library misuses terminology  this does not supersede the RFC  Instead  it imposes a burden of responsibility on users of that library to understand both interpretations and to be careful with words and context  Where RFCs do not agree  the most recent and most directly applicable RFC takes precedence  References  TCP-IP Illustrated Volume 1 The Protocols  W  Richard Stevens  1994 Addison Wesley  RFC793  Information Sciences Institute  University of Southern California for DARPA  RFC147  The Definition of a Socket  Joel M  Winett  Lincoln Laboratory

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Socket is SW abstraction of networking endpoint  used as the interface to the application  In Java  C  it is represented by object  in Linux  Unix it is a file    Port is just a property of a socket you have specify if you want to establish a communication  To receieve packet from a socket you have to bind it to specific local port and NIC  with local IP address  or all NICs  INADDR ANY is specified in the bind call   To send packet  you have to specify port and IP of the remote socket

User · Answer

After reading the excellent up-voted answers  I found that the following point needed emphasis for me  a newcomer to network programming   TCP-IP connections are bi-directional pathways connecting one address port combination with another address port combination  Therefore  whenever you open a connection from your local machine to a port on a remote server  say www google com 80   you are also associating a new port number on your machine with the connection  to allow the server to send things back to you   e g  127 0 0 1 65234    It can be helpful to use netstat to look at your machine s connections    gt  netstat -nWp tcp  on OS X  Active Internet connections Proto Recv-Q Send-Q  Local Address          Foreign Address         state      tcp4       0      0  192 168 0 6 49871      17 172 232 57 5223     ESTABLISHED

User · Answer

I know that there are lot of explanations  But  there is one more easy way to understand with practical example  We all can connect to HTTP port 80  but does it mean only one user can connect to that port at a time   The answer is obviously  no   Multiple users for multiple purposes can access HTTP port 80 but they still get proper response they are waiting for  from the server  can t they   Now think about it for a minute  how       Yes you are correct  its IP address that uniquely identifies different users who contacts for different purposes  If you would have read the previous answers before reaching here  you would know that IP address is a part of information that socket consists  Think about it  is it possible to have a communication without sockets   The answer is  Yes  but you cannot run more than one application in a port but we know that we are not a  Dump  switch that runs on just hardware

User · Answer

A socket is a data I O mechanism  A port is a contractual concept of a communication protocol  A socket can exist without a port  A port can exist witout a specific socket  e g  if several sockets are active on the same port  which may be allowed for some protocols    A port is used to determine which socket the receiver should route the packet to  with many protocols  but it is not always required and the receiving socket selection can be done by other means - a port is entirely a tool used by the protocol handler in the network subsystem  e g  if a protocol does not use a port  packets can go to all listening sockets or any socket

[networking] What is the difference between a port and a socket?

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