Tuesday, May 28, 2013

What Is a Port Number (Logical Port)?

In computer networking, the term port can refer to either physical or virtual connection points.
When considering computer networks, there are two kinds of port that we deal with - Physical Ports and Logical Ports. 

Physical network ports allow connecting cables to computers, routers, modems and other peripheral devices. Several different types of physical ports available on computer network hardware.
A physical port, as opposed to a virtual or logical port is an interface on a computer into which you can insert a connector for a device.
Examples of Physical Port : RJ45 port (Ethernet/LAN/NIC Port), Serial Port (RS-232), USB Port.

Virtual ports are part of TCP/IP networking. These ports allow software applications to share hardware resources without interfering with each other. Computers and routers automatically manage network traffic traveling via their virtual ports. Network firewalls additionally provide some control over the flow of traffic on each virtual port for security purposes.

Logical Port :

In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint in a computer's host operating system. A port is associated with an IP address of the host, as well as the type of protocol used for communication. The purpose of ports is to uniquely identify different applications or processes running on a single computer and thereby enable them to share a single physical connection to a packet-switched network like the Internet.

The protocols that primarily use ports are the Transport Layer protocols, such as the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) of the Internet Protocol Suite. A port is identified for each address and protocol by a 16-bit number, commonly known as the port number. The port number, added to a computer's IP address, completes the destination address for a communications session. That is, data packets are routed across the network to a specific destination IP address, and then, upon reaching the destination computer, are further routed to the specific process bound to the destination port number.
Note that it is the combination of IP address and port number together that must be globally unique. Thus, different IP addresses or protocols may use the same port number for communication; e.g., on a given host or interface UDP and TCP may use the same port number, or on a host with two interfaces, both addresses may be associated with a port having the same number.

In computer networking, a port number is part of the addressing information used to identify the senders and receivers of messages. Port numbers are most commonly used with TCP/IP connections. Home network routers and computer software work with ports and sometimes allow you to configure port number settings. These port numbers allow different applications on the same computer to share network resources simultaneously.

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How Port Numbers Work

Port numbers are associated with network addresses. For example, in TCP/IP networking, both TCP and UDP utilize their own set of ports that work together with IP addresses.
Port numbers work like telephone extensions. Just as a business telephone switchboard can use a main phone number and assign each employee an extension number (like x100, x101, etc.), so a computer has a main address and a set of port numbers to handle incoming and outgoing connections.
In both TCP and UDP, port numbers start at 0 and go up to 65535. Numbers in the lower ranges are dedicated to common Internet protocols (like 21 for FTP and 80 for HTTP).

Port numbers are typically processed by network hardware and software automatically. Normally you will not see them while casually using a network nor need to take any action involving them. However, in these special cases you can work with network port numbers:When You May Need to Take Action with Port Numbers

  • network administrators may need to set up port forwarding to allow the port numbers of specific applications to pass through a firewall. On home networks, broadband routers support port forwarding on their configuration screens.
  • network programmers sometimes need to specify port numbers in their code, such as in socket programming.
  • sometimes, a Web site URL will require a specific TCP port number be included. For example, http://localhost:8080/ uses TCP port 8080. Again, this is more usually seen in software development environments than on the Internet.
For List Of UDP and TCP Port Numbers Please Visit this LINK :

In TCP/IP and UDP networks, a port is an endpoint to a logical connection and the way a client program specifies a specific server program on a computer in a network. Some ports have numbers that are pre-assigned to them by the IANA, and these are called the "well-known ports" which are specified in RFC 1700.
Port numbers range from 0 to 65536, but only ports numbers 0 to 1024 are reserved for privileged services and designated as well-known ports. This list of well-known port numbers specifies the port used by the server process as its contact port.
Port NumberDescription
1TCP Port Service Multiplexer (TCPMUX)
5Remote Job Entry (RJE)
18Message Send Protocol (MSP)
20FTP -- Data
21FTP -- Control
22SSH Remote Login Protocol
25Simple Mail Transfer Protocol (SMTP)
42Host Name Server (Nameserv)
49Login Host Protocol (Login)
53Domain Name System (DNS)
69Trivial File Transfer Protocol (TFTP)
70Gopher Services
103X.400 Standard
108SNA Gateway Access Server
115Simple File Transfer Protocol (SFTP)
118SQL Services
119Newsgroup (NNTP)
137NetBIOS Name Service
139NetBIOS Datagram Service
143Interim Mail Access Protocol (IMAP)
150NetBIOS Session Service
156SQL Server
179Border Gateway Protocol (BGP)
190Gateway Access Control Protocol (GACP)
194Internet Relay Chat (IRC)
197Directory Location Service (DLS)
389Lightweight Directory Access Protocol (LDAP)
396Novell Netware over IP
444Simple Network Paging Protocol (SNPP)
458Apple QuickTime
546DHCP Client
547DHCP Server
For further information, see RFC 1700.