Shulou(Shulou.com)06/01 Report--

Computer network: a system in which multiple computers located at different geographical locations and operating independently are connected by communication equipment and lines, and corresponding systems and application software are configured to realize software and hardware resource sharing and information transmission among originally independent computers.

Functions of computer networks:

Data communication 2. Resource sharing Increased reliability 4. Improve system processing capacity

ARPANET: ARPANET was born in 1969, which is a milestone in the development of computer networks and the basis for Internet implementation.

Network protocols and standards:

Protocol: "rules"; a protocol is a set of rules governing data communication;

Three elements of the agreement:

Syntax: Structure and form of data Semantics: Yes Meaning of each part Synchronization: When data is sent and how often data is sent

Criteria: "consensus rule";

ISO: International Organization for Standardization

OSI: Open Systems Interconnection

ANSI: American National Bureau of Standardization

ITU-T: International Telecommunication Union--Telecommunication Standards Division

IEEE: Institute of Electrical and Electronics Engineers

IEEE802 local area network standard: It defines how network cards access transmission media (such as twisted pair, optical fiber, wireless, etc., which are commonly used at present) and how data is transmitted on these media.

LAN: local area network MAN: metropolitan area network WAN: wide area network

IEEE 802.3 standard

IEEE 802.3U Standard: 100Mb/s Fast Ethernet Standard

IEEE802.3z Standard: Fiber Optic Media for 1Gb/s Ethernet Standard

IEEE802.3ab Standard: Twisted Pair for 1Gb/s Ethernet

IEEE 802.3ae standard: 10Gb/s Ethernet standard

IEEE 802.3ba Standard: 100Gb/s Ethernet Standard

the IEEE 802.11 standard

IEEE 802.a standard: carrier frequency 5GHz, maximum rate 54Mb/s

IEEE 802.b standard: carrier frequency 2.4 GHz, maximum rate 11Mb/s

IEEE 802.g standard: carrier frequency 2.4GHz, maximum rate 54Mb/s

IEEE802.n Standard: The most widely used technology at present, the highest rate of 600Mb/s

1. switching routing equipment

The primary device used in computer networks to find reasonable paths for data packets

Switches: (1) The switches at the bottom layer are mainly used to connect the hosts in the local area network, have the function of learning MAC addresses, and realize high-speed data exchange between these hosts by using the learned address information;(2) The switches at the middle and upper layers are used to connect the switches at the bottom layer, integrating each small network into a large network with logic and hierarchy. It also generally has routing functions, and some also provide simple security features.

2. network security device

Firewall: A security barrier like a network that enforces access control policies on traffic flowing between different network zones.

(2) ××× equipment: Virtual private network, *** equipment can encrypt and transmit key service data, and the data will be cracked when transmitted to the receiver, thus ensuring the security of data during transmission.

3. wireless network device

Wireless network devices are network devices designed based on wireless communication protocols. Common wireless network devices include wireless routers, wireless network cards, wireless bridges, etc.

Network equipment manufacturers

(1) Cisco

(2) Huawei Company

(3) H3C (formerly Huawei 3COM Company, a joint venture between Huawei and 3COM Company of the United States)

Network topology refers to the physical layout of various devices interconnected by transmission media, that is, how to connect computers and network devices in the network. Generally, there are star topology, bus topology, ring topology, network topology, etc.

(1) Star topology

Advantages: easy to implement; easy to network expansion; easy to troubleshoot.

Disadvantages: high pressure on central nodes; high networking costs.

(2) Network topology

Each node in the network topology is connected to at least two other nodes. The biggest advantage of this topology is high reliability. There is a main link and a backup link between any two nodes in the network, but these redundant lines themselves cause the construction cost of the network to increase exponentially.

Network topology can be divided into two types: full network topology and partial network topology.

A full-network topology refers to the interconnection of any node with all other nodes in the network structure. This network structure truly realizes that any point or points of failure will not affect other nodes. But in practice, this structure is rare, mainly because it is too expensive and really unnecessary.

Partial network topology includes all network topologies except full network topology, which is a common topology structure at present. Because the pressure of the core network is relatively large, once the core switch fails, it will be intended to communicate with the whole network, so in the initial design of the network, two core switches are generally prepared for each other, and any branch switch has two links to the core switch, so even if one of the core devices or one link fails, it will not affect the normal operation of the network.

IP address definition: 32-bit binary number divided into 4 segments, each segment 8 bits, separated by the origin

IP address classification: network part and host part, network part is used to identify different networks, host part is used to identify a specific host.

There are five categories:

Class A: 1-126 ; suitable for large networks; maximum number of hosts: 224

Class B: 128-191 ; suitable for medium-sized networks; maximum number of hosts 216

Class C: 192-223 ; suitable for small networks; maximum number of hosts 28

Class D: 224-239 ; addresses used for multicast communications

Category E: 240-255 ; reserved address for scientific research

Private addresses (not available on the Internet):

 10.0.0.0 ~ 10.255.255.255

 172.16.0.0 ~ 172.31.255.255

 192.168.0.0 ~ 192.168.255.255

127.0.0.1 Is the local loopback address, there are two main functions: one is to test the network configuration of the machine, can Ping through 127.0.0.1 indicates that the machine's network card and IP protocol installation are no problem; Second, some SERVER/CLIENT applications need to call the resources on the server when running, generally to specify the IP address of SERVER, but when the program wants to run on the same machine and there is no other SERVER, you can install the SERVER resources on the local machine, SERVER IP address device 127.0.0.1 can also run.

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