Layer-4 Exchange Technology Analysis

In layer-4 switching, the TCP and UDP headers contain port numbers, which uniquely differentiate which application protocols (such as HTTP and FTP) are contained in each packet ). The endpoint system uses this information to distinguish packet data, especially the port number, so that a computer system at the receiving end can determine the type of the IP packet it receives and hand it over to appropriate high-level software. A combination of port numbers and device IP addresses is usually called "socket )". The port numbers between 1 and 255 are retained. They are called "well-known" ports, that is, these ports are the same in all TCP/IP protocol stack implementations of the host. In addition to "well-known" ports, standard UNIX services are allocated in the range of port 256 to port 1024. custom applications generally allocate port numbers over port 1024. you can find the latest list of allocated port Numbers on RFc1700 "Assigned Numbers. The additional information provided by the TCP/UDP port number can be used by the network switch, which is the basis for layer-3 switching.

Example of "familiar" Port Number:

Application Protocol port number

FTP 20 (data)

21 (Control)

TELNET23

SMTP 25

HTTP 80

NNTP 119

NNMP 16

162 (SNMP traps)

The additional information provided by the TCP/UDP port number can be used by the network switch, which is the basis for layer-4 switching.

A vswitch with the layer-4 function can act as the "virtual IP" (VIP) frontend connected to the server.

Each server and server group supporting a single or common application is configured with a VIP address. This VIP address is sent and registered on the domain name system.

1. Introduction to the fourth layer switch technology
2. What is layer-7 switch?