The protocol number is the value contained in the protocol field of an IPv4 header. It is used to identify the log. This is an 8-bit file. In IPv6, this field is called the «Next Header» field. Some of the protocol numbers of commonly used routing protocols are given below:Protocol protocol numberEIGRP 88OSPF 89 When the kernel receives IP packets, how does it know what they represent? Are they part of a TCP stream, a UDP datagram, or something else? Known ports are standardized port numbers that allow remote computers to know which port to connect to for a particular network service. This simplifies the connection process because both the sender and recipient know in advance that the data related to a particular process is using a specific port. For example, all systems that offer Telnet do so on port 23. Hello! amirkh1566, I`m not sure ip=0 what do you mean? Can you please elaborate on that? Thank you port numbers are not unique between transport layer protocols. Numbers are unique only in a specific transport protocol. In other words, TCP and UDP can use the same port numbers. It is the combination of protocol and port numbers that uniquely identifies the specific process to which the data should be delivered. The combination of an IP address and a port number is called a socket. A socket uniquely identifies a single network process throughout the Internet.
Sometimes the terms «socket» and «port number» are used interchangeably. In fact, well-known services are often referred to as «known outlets.» In the context of this discussion, a «socket» is the combination of an IP address and a port number. A pair of sockets, one socket for the receiving host, and one for the sending host, define the connection for connection-oriented protocols such as TCP. The answer is that all IP packets contain an IP protocol number. This is the ninth byte of the packet. Each protocol that runs over IP has its own number. TCP is number 6; UDP is number 17. Some protocol and port numbers are reserved to identify known services. Well-known services are standard network protocols such as FTP and Telnet, which are often used throughout the network. Protocol numbers and port numbers associated with known services are documented in the RFC Assigned Numbers. UNIX systems define protocol and port numbers in two simple text files.
After IP transmits the incoming data to the transport protocol, the transport protocol transmits the data to the appropriate application process. Application processes (also known as network services) are identified by port numbers, which are 16-bit values. The source port number, which identifies the process that sent the data, and the destination port number, which identifies the process that will receive the data, are included in the first header word of each TCP segment and UDP packet. In the Telnet example, the first user gets a random source port number and a destination port number of 23 (Telnet). The second user gets a different random source port number and the same destination port. This is the pair of port, source, and destination numbers that uniquely identifies each network connection. The destination host knows the source port because it is provided in both the TCP segment header and the UDP packet header. Both hosts know the destination port because it is a known port.
A port number is an address for some Layer 4 protocols (TCP or UDP). The port number is used by the Layer 4 protocol to determine which application receives the payload from the Layer 4 datagram. The port number defines the number of protocols in an application layer. Can anyone explain it clearly? I know that port numbers are used by applications to distinguish the services you have requested, and routing protocols use protocol numbers in the TCP header. You can see them all on /etc/protocols on your computer! The official list is maintained by the Internet Assigned Numbers Authority (IANA) here: www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml On a UNIX system, protocol numbers are defined in /etc/protocols. This file is a simple table that contains the log name and the protocol number associated with that name. The format of the table is a single entry per row, consisting of the official name of the protocol, separated by spaces of the protocol number. The log number is separated by spaces in the alias of the log name. Comments in the table start with #. A /etc/protocols file is shown below: In TCP/IP, a port is a software endpoint in an operating system. Each port is assigned a number. This is called the port number.
A port number can be between 0 and 65535. There are UDP and TCP port numbers in the same range. Port numbers are used by Transmission Control Protocol (TCP) and User Datagram Protocol (UDP), while protocol numbers are reserved numbers used to identify protocols A protocol is simply the language in which both applications accept conversation at both ends. If your app sends byte streams to my app, my app needs to know how to interpret those bytes. The protocol number is used by layer 3 (IPv4 or IPv6) to determine which layer 4 protocol in the network stack to send the packet payload. Once the data has been routed over the network and transmitted to a specific host, it must be transmitted to the appropriate user or process. As data moves up or down on the TCP/IP layers, a mechanism is needed to provide it to the right protocols in each layer. The system must be able to combine data from many applications into a few transport protocols and transport protocols into the Internet Protocol. Combining multiple data sources into a single stream is called multiplexing. The protocol number is a single byte in the third word of the datagram header. The value identifies the protocol in the IP layer to which the data is to be transmitted.
Let`s take the example of dynamically assigned ports and known ports. For example, suppose a user on host 172.16.12.2 uses Telnet to connect to host 192.168.16.2. Host 172.16.12.2 is the source host. A unique port number is dynamically assigned to the user: 3382. The connection is established to the Telnet service on the remote host, to which known port 23 is assigned according to the standard. The socket for the source side of the connection is 172.16.12.2.3382 (IP address 172.16.12.2 plus port number 3382). For the connection landing page, the socket is 192.168.16.2.23 (address 192.168.16.2 plus port 23). The target socket port is known to both systems because it is a known port. The source socket port is known because the source host informed the source socket destination host when the connection request was made. Therefore, the socket pair is known to the source and destination computers. The combination of the two sockets clearly identifies this connection; no other connection on the Internet has this pair of sockets. You can think of a port as a phone extension, where the computer`s IP address is like its phone number.
You can call the number (IP address) to communicate with the computer, and then dial the extension (port) to communicate with a specific application. An application must listen on a port in order to communicate. The protocol number defines the field in the IP header to which the protocol should be transmitted. What exactly does this table mean? When a datagram arrives and its destination address matches the local IP address, the IP layer knows that the datagram must be transmitted to one of the transport protocols above. To decide which protocol to receive the datagram, IP examines the protocol number of the datagram. You can use this table to see that if the datagram protocol number is 6, IP delivers the datagram to TCP. If the protocol number is 17, IP transmits the datagram to UDP. TCP and UDP are the two transport-layer services we deal with, but all the protocols listed in the table use the IP datagram delivery service directly.
Some, such as ICMP, EGP and GGP, have already been mentioned. You don`t have to worry about smaller protocols. A socket consists of an IP address( in the IP ADDRESS we have one of the fields for the protocol number) and a port number, so now when you hear a specific port number, you can receive messages from remote machines The list above is the contents of the /etc/protocols file from a Solaris 2.5.1 workstation. This list of figures is by no means exhaustive. If you refer to the Protocol Numbers section of the RFC Assigned Numbers, many other protocol numbers are displayed. However, a system only needs to contain the number of protocols it actually uses. Even the above list is more than that particular workstation needs, but the extra entries don`t hurt. There is a second type of port number called dynamically assigned port.
As the name suggests, dynamically assigned ports are not pre-assigned. If necessary, they are assigned to processes. The system ensures that it does not assign the same port number to two processes and that the assigned numbers are greater than the range of default port numbers. Data from the network must be demultiplexed: divided to be delivered to several processes. To perform this task, IP uses protocol numbers to identify transport protocols, and transport protocols use port numbers to identify applications. On UNIX systems, port numbers are defined in the /etc/services file. There are many more network applications than transport layer protocols, as shown by the size of the table. Port numbers below 256 are reserved for known services (such as FTP and Telnet) and are defined in the assigned RFC numbers. Ports with a number between 256 and 1024 are used for UNIX-specific services, services such as rlogin, which were originally developed for UNIX systems.
However, most of them are no longer UNIX-specific. I am a little confused about the concept of port number and protocol number. someone can define that. I know that the port number is given to the protocols that run on L4 and the protocol number is given to the protocol that runs at the network level….