Basic knowledge of network devices

 

Theory

Physical Layer: a feature that transmits binary bits over physical connections and defines mechanical, electrical, functional, and specification features.

Mechanical Characteristics: interface plug-in shape, size...

Electrical Characteristics: Level and impedance of binary bit streams

Feature: Function Definition of multiple signal lines, which are generally divided into data lines, control lines, and ground lines;

Procedure features: working rules and timing of Signal Lines

 

 

Data link layer: function Link Management, frame transmission, traffic control, and error control;

Frame: packages with strict logic and highly optimized data are encapsulated;

Frame composition: First and end signs 01 111, 0 bit insertion/deletion technology, address field a, control field C, Data Information Field Z, frame verification field FCs

Mac: Media Access Control

 

Network Layer: Route Selection and Traffic Control

Network-layer traffic limit: restrict the amount of data that enters the group exchange network;

 

 

Devices: physical layer, repeater, signal copy, amplification, adjustment, and other functions to increase the signal transmission distance;

Data link layer, bridge, switch

 

Hub:

Distribute the data received on a port to all ports;

Extension Method:

STACK: shared bandwidth. Data is transmitted on only one port at a time, which reduces the average bandwidth. The backplane is logically a separate device;

Cascade: uplink port, logically multiple devices;

 

Transceiver:

Used to connect a computer to different transmission media

 

Nic

Function: encapsulate frames and process frames;

 

Repeater,

Receives, copies, transmits, and zooms in two or more network segments physically;

Bridge: isolated subnets. Communications within the LAN are isolated;

 

Vswitch:

Back bus, internal switching matrix, all ports mounted on back bus;

Exchange refers to the automatic transmission of information by humans or devices according to the needs of transmitting information at both ends of the communication,Technology that sends the information to be transmitted to the corresponding route that meets the requirements

Data transmission between multiple port pairs at the same time

Find the port on which the NIC that owns the MAC address is mounted Based on the MAC address of the packet, and then send the data directly to the port. If the port does not exist, broadcast the data;

You can mount multiple MAC addresses on the same port.

STACK: logically turn multiple switches into one device;

Virtual LAN: divides several ports of a vswitch into one group to form a VLAN. The vswitch isolates the broadcast data between VLANs ;--

VLAN Division: Port, MAC address, IP address, and Policy Service

Layer-3 Switch: Provides subnet intercommunication capabilities. It is applicable to scenarios where multiple subnets need to be interconnected;

 

Router:

Connect multiple logically separate networks (subnets or separate networks) to forward data, exchange network topology information through the routing protocol, and dynamically generate a route table accordingly;

Route table:

Destination subnet (or address)
Subnet Mask gateway flag
Interface

201.66.37.0 255.255.255.0 201.66.37.12
U/h/g

Send all data sent to the destination subnet through the interface. If the flag is g, the data is sent to the Gateway. Otherwise, the data is directly sent to the host.

The same interface can be sent to multiple destination subnets. For the NIC of the host, the data "local subnet and gateway" is available, and all data from non-local subnets will be sent to the gateway; A Nic has only one gateway. How can this problem be solved?

U: Up Status

 

An example of a route table:

 

Destination Address Mask gateway id mss Interface Name

127.0.0.1 255.0.0.0 0.0.0 . 0 uh
3984 Lo

167.102.1.0 255.255.255.0 0.0.0 . 0 U
1500 eth0

0.0.0 . 0 0.0.0 . 0 167.102.1.1 UG
1500 eth0

Dynamic Route table: the route periodically broadcasts its route table information to the adjacent Route. After the other party obtains the information, it will know the subnets that can be reached through it and update its route table items.

Flag: h indicates that the destination address is a host; G to the destination address must pass through the gateway; H and G are not opposite sides.

 

Bridge:

Expansion: Network Distance

Filter: isolate unnecessary data between networks

Forward: forward data in one CIDR block to another CIDR block.

Self-learning capability: When receiving data, write down the source address and the LAN of the Data Source

 

 

Problem:

1, What if only half of the formatted data is transmitted over TCP? The other party must determine whether the received data is a complete data block;

2, How can multiple threads write formatted data to the same socket to avoid data block writing disorder?

3, TCPThe data written into the buffer at the application layer cannot be successfully transmitted to the target party.For example, the application cannot know whether the other party has executed the command, even if the other party has confirmed it, because the confirmation may not be sent back. What should I do?

4, Lan, physical layer concept, the area where a physical broadcast package can arrive; subnet, IP layer concept, the area where an IP broadcast package can arrive;