Introduction to TCP/IP

I. TCP/IP Beijing and introduction

In the 70 's, with the development of computer technology, computers users realized that it was necessary to connect computers from all over the world to play a more important role in computer. But the simple connection is not enough, because the computer can not communicate. Therefore, the design of a common "language" to communicate is necessary to be less, then the TCP/IP protocol was born.

TCP/IP (transmission Control protocol/internet Protocol) is the short name for transmission protocol and network protocols, which defines how point devices connect to the Internet and how data is transferred between them. TCP/IP is not a protocol, but a general term for a protocol family that includes IP protocols, ICMP protocols, TCP protocols, and HTTP, FTP, POP3 protocols, and so on. Computers in the network are interconnected using this set of protocols.

Second, network protocol stack architecture

Refers to the network protocol stack architecture, the most famous is the OSI seven layer model, but the TCP/IP protocol family structure is slightly different, the hierarchy between them:

Visible TCP/IP is divided into 4 layers, each layer of the task is not the same, each layer of the work of the Protocol is not in the same way, each layer of packaging data in the upper level is not the same.

(1) Application layer: The application through this layer to access the network, common FTP, HTTP, DNS and TELNET protocol;

(2) Transport layer: TCP protocol and UDP Protocol;

(3) Network layer: IP protocol, ARP, RARP protocol, ICMP protocol, etc.

(4) Network interface layer: is the base of TCP/IP protocol, responsible for sending and receiving data frames.

III. Preparation of knowledge

1. IP Address

Each node on the network must have a separate IP address, usually using an IP address that is a 32bit number. into 4 groups, for example, 255.255.255.255 is an IP address. With an IP address, the user's computer can discover and connect to another computer on the Internet.

2. Domain Name

12-digit IP address is difficult to remember, in the actual application, the user generally do not need to remember the IP address, the Internet to each IP address an alias, used to be called domain name. For example: Baidu's IP address is 119.75.218.70, but in fact most of the time we are through the domain name www.baidu.com access to the URL, because it is more in line with people's memory logic. The domain name corresponds to the IP address of the computer and stores the correspondence in the Domain Name service, which allows the user to communicate with the specified computer by remembering the domain name. Common domain names include COM, net, and org three top-level domain suffixes, in addition to each country has its own country-specific domain name suffix (such as our country's domain name suffix cn). Currently used domain names such as Baidu (www.baidu.com), the Linux Organization (www.lwn.net) and so on. In the Windows command line we can use the command nslookup or ping to view the IP address that corresponds to the domain name.

3. MAC Address

MAC (Media Access Control) address, or physical address, or hardware address, used to define the location of devices in the Internet. In the TCP/IP hierarchy model, the network layer manages the IP address, and the link layer is responsible for the MAC address. So each network location will have an IP address dedicated to it, and each host will have a dedicated MAC address.

4. Port number

IP addresses are used to discover and find addresses in a network, but how different programs communicate with each other requires a port number to identify them. If the IP address is likened to a house, the port is the door to the house. The real house has only a few doors, but the port is identified by a 16-bit number, and an IP address can have a port of 65536 (that is: 2^16)! The server's default programs are generally identified by the port numbers that are known to them. For example, for each TCP/IP implementation, the TCP port number of the SMTP (Simple Mail Transfer Protocol) server is either the TCP port number of the 25,FTP (File Transfer Protocol) server or the UDP port number of the 21,tftp (Simple File Transfer Protocol) server is 69. Any TCP/IP implementation provides a service that uses a well-known port number between 1-1023. These known port numbers are managed by the Internet Port number assignment Authority (internet Assigned Numbers Authority, IANA).

5. Encapsulation and Separation

Encapsulation: When the application sends data, the data goes from top to bottom through each layer in the protocol hierarchy, each layer adds some header or trailer information to the data, as shown in the data unit passed to the network layer by the transport layer called the TCP Packet segment (TCP segment) or the UDP datagram (UDP Datagram). The data unit that the network layer passes to the link layer is called an IP datagram (IP datagram). The transmission unit on the link layer is called a frame.

divide : When the host receives a data frame, the data rises from the bottom of the protocol layer, passing each layer, checking and removing the corresponding level of the packet header or tail, and the package process is the opposite.

6. RFC

The RFC (Request for Comment) documentation is the official standard for all Ethernet protocols and is published on its official web site, developed by the IETF Standards Association. A large number of RFCs is not a formal standard, and the purpose of publication is simply to provide information. The length of the RFC varies from a few pages to hundreds of pages. Each protocol is identified by a number, such as RFC 3720 is the standard for the ISCSI protocol, and the larger the number, the more recent the content of the RfC is, or the corresponding protocol (standard) that appears later.

All RFC documents can be found on the web and are on the IETF's website. On the site, you can quickly find RFC documents for the target protocol by category and search. There are currently thousands of RFC documents on the IETF website, but we do not need to master all, in the work or study if the corresponding interpretation can be found, the theory and the actual combination will have a better effect, simply read the effect of the RFC generally.

Introduction to TCP/IP