Introduction to several operation logics in C Language

MTU: Maximum Transmission Unit (MTU) refers to the Maximum data packet size (in bytes) that can be passed on a layer of a communication protocol ). The maximum transmission unit parameter is usually related to the communication interface (network interface card, serial port, etc ).

The Chinese name of a VLAN (Virtual Local Area Network) is "Virtual LAN ". VLAN is a new data exchange technology that logically divides LAN devices into network segments to implement virtual working groups.

Wireless Local Area Networks (WLAN) is a very convenient data transmission system. It uses the Radio Frequency (RF) technology to replace the outdated Coaxial copper wire) the local area network makes it possible for users to use a simple access architecture to achieve the ideal state of "Portable Information and convenient access to the world.

Virtual Private Network (VPN) refers to the technology for establishing a Private Network on a public Network. It is called virtual network, mainly because the connection between any two nodes of the VPN network does not have the end-to-end physical link required by the traditional private network, but is built on the network platform provided by the public network service provider, such as Internet, ATM (asynchronous transmission mode>, Frame Relay (Frame Relay), and other logical networks. User data is transmitted in a logical link. It covers extensions of private networks that encapsulate, encrypt, and authenticate links across shared networks or public networks. VPN mainly uses the color tunnel technology, encryption and decryption technology, key management technology and user and device identity authentication technology.

Network Layer-a very important field in the packet format is called the Protocol Number. For example, for TCP connections on the transport layer, the Protocol number in the IP packet on the network layer will have a value of 6. For UDP, the value is 17 --- transport layer.

Transport Layer --- associate through interfaces (the port field is called Port) --- application layer.

Use netstat-an to view the port opened on the local machine.

The proxy server uses the following ports:

(1) common port number of the HTTP Proxy Server: 80/8080/3128/8081/9080

(2) SOCKS proxy protocol server port: 1080

(3) FTP (file transfer) protocol Proxy Server common port: 21

(4) Telnet protocol Proxy Server common port: 23

HTTP server. The default port number is 80/tcp (this port is enabled for Trojan Executor );

HTTPS (securely transferring web pages) server. The default port number is 443/tcp 443/udp;

Telnet (Insecure text transfer). The default port number is 23/tcp (port opened by Tiny Telnet Server );

FTP. The default port number is 21/tcp (ports opened by Doly Trojan, Fore, Invisible FTP, WebEx, WinCrash, and Blade Runner );

TFTP (Trivial File Transfer Protocol), the default port number is 69/udp;

SSH (secure logon), SCP (file transfer), and port redirection. The default port number is 22/tcp;

SMTP Simple Mail Transfer Protocol (E-mail ), the default port number is 25/tcp (this port is enabled for Trojan Antigen, Email Password Sender, Haebu Coceda, Shtrilitz Stealth, WinPC, and WinSpy );

POP3 Post Office Protocol (E-mail), the default port number is 110/tcp;

WebLogic. The default port number is 7001;

The default port number of the Webshpere application is 9080;

Webshpere management tool. The default port number is 9090;

JBOSS. The default port is 8080;

TOMCAT. The default port number is 8080;

WIN2003 remote login, the default port number is 3389;

Symantec AV/Filter for MSE, default port: 8081;

The default port number of the Oracle database is 1521;

Oracle emctl. The default port is 1158;

Oracle XDB (XML database), default port: 8080;

Oracle xdb ftp service. The default port number is 2100;

Ms SQL * SERVER database server, the default port number is 1433/tcp 1433/udp;

Ms SQL * SERVER database monitor, the default port number is 1434/tcp 1434/udp;

QQ. The default port number is 1080/udp.