Computer network: Use communication equipment and lines to connect multiple computers located in different geographical locations and operate relatively independently, and configure corresponding systems and application software to realize software and hardware resource sharing and information transmission between the original independent computers. systems with equal functions
Functions of computer network:
- Data communication 2. Resource sharing 3. Increase reliability 4. Improve system processing capacity
ARPANET: ARPANET was born in 1969. It is a milestone in the development of computer networks and the basis for the realization of the Internet.
Network protocols and standards:
- Protocol: "rules"; a protocol is a set of rules that control data communication;
three elements of a protocol: - Syntax: Structure and Form of Data
- Semantics: is the meaning of each part
- Synchronization: When and how often data is sent
Criteria: "Agreed Rules";
ISO: International Organization for Standardization
OSI: Open Systems Interconnection
ANSI: American National Bureau of Standardization
ITU-T: International Telecommunication Union-Telecommunications Standards Division
IEEE: Institute of Electrical and Electronics Engineers
IEEE802 local area network standard: It defines how network cards access transmission media (such as the more commonly used twisted pair, optical fiber, wireless, etc.), as well as methods for transmitting data on these media.
Divided by geographical scope: LAN: Local Area Network MAN: Metropolitan Area Network WAN: Wide Area Network
IEEE 802.3 standard
IEEE802.3U standard: 100Mb/s Fast Ethernet standard IEEE802.3z
standard: Optical fiber medium implements 1Gb/s Ethernet
standard
/s Ethernet standard
IEEE802.3ba standard: 100Gb/s Ethernet standard
IEEE802.11 standard
IEEE802.a standard: carrier frequency 5GHz, maximum rate 54Mb/s
IEEE802.b standard: carrier frequency 2.4GHz, maximum rate 11Mb/s
IEEE802.g standard: carrier frequency 2.4GHz, maximum rate 54Mb/s
IEEE802. n Standard: The most widely used technology at present, the highest rate is 600Mb/s
1. Switching and routing equipment
Router: The main equipment
switch used to find a reasonable path for data packets in a computer network : (1) The underlying switch is mainly used to connect hosts in the local area network, has the function of learning MAC addresses, and uses the learned MAC address. (2) The middle and high-level switches are used to connect the bottom switches, and integrate each small network into a large network with logic and hierarchy. Generally, it also has routing functions, and some also provide simple security features.
2. Network security equipment
(1) Firewall: Like a network security barrier, it can enforce access control policies on traffic flowing through different network areas.
(2) VPN equipment: virtual private network, VPN equipment can encrypt and transmit key business data, and the data will be cracked when it is transmitted to the receiver, thus ensuring the security of data during transmission.
3. Wireless network devices
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 Cisco
(2) Huawei
(3) H3C (formerly known as Huawei 3COM, a joint venture between Huawei and US 3COM)
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, mesh topology and so on.
(1) Advantages of star topology
: easy to implement; easy to expand the network; easy to troubleshoot.
Disadvantages: high pressure on the central node; high networking cost.
(2) Net topology
Each node in the net topology is connected to at least two other nodes. The biggest advantage of this topology is high reliability. There is a primary link and a backup link between any two nodes in the network at the same time, but these redundant lines themselves cause the network construction cost to increase exponentially.
There are two types of mesh topologies: full mesh topology and partial mesh topology.
The whole network topology means that any node in the network structure is interconnected with all other nodes. This kind of network structure truly realizes that any one or several points of failure will not affect other nodes. But in practice, this structure is rare, mainly because the cost is too high, and it is really unnecessary.
Partial mesh topology includes all mesh topologies except the full mesh topology, and is a relatively common topology at present. Due to the high pressure on the core network, once the core switch fails, the communication of the entire network will be intended. Therefore, when the network is initially designed, two core switches are generally prepared as backups for each other, and any branch switch to the core switch is connected to the core switch. There are two links, so even if one of the core devices or one link fails, it will not affect the normal operation of the network.
IP address
IP address definition: The 32-bit binary number is divided into 4 segments, each segment is 8 bits, and the middle is separated by the origin.
IP address classification: network part and host part, the network part is used to identify different networks, and the host part is used to identify a specific host.
It is divided into five categories:
Class A: 1-126; suitable for large-scale 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 In small networks; the maximum number of hosts is 28
Class D: 224-239; addresses used for multicast communication
Class E: 240-255; private addresses reserved for scientific research
(cannot be used 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. It has two main functions: one is to test the network configuration of the machine, and being able to ping 127.0.0.1 means that there is no problem with the network card and IP protocol installation of the machine; the other is some SERVER/CLIENT The application program needs to call the resources on the server when it is running. Generally, the IP address of the SERVER needs to be specified, but when the program wants to run on the same machine without other SERVERs, the SERVER resources can be installed on the local machine. SERVER A device with an IP address of 127.0.0.1 will work just as well.