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

Local area network and wide area network, simple, intuitive and economical expression

Local area network: spend money on equipment and guaranteed bandwidth

Wan: spend money on bandwidth

Server and client

1. From a hardware point of view: the client is an ordinary computer, and the server is a computer dedicated to providing services, which is different from that of ordinary use.

two。 From the software point of view: the client is the computer with the request service software, and the server is the computer with the service.

OSI reference model

Seven-tier model:

Application layer: an application that can generate network traffic.

Presentation layer: encryption, compression and coding of data generated by the application layer

Session layer: establish a session to maintain contact between the server and the client (can be viewed by typing netstat-n at the command prompt)

Transport layer: reliable transmission (TCP protocol), unreliable transmission (UDP protocol) (three-way handshake flow control packet loss retransmission)

Network layer: choosing the best path, network address planning

Data link layer: how to identify the start and end of data frames for MAC addresses of network devices, error checking

Physical layer: define the interface, voltage and other physical standards of network equipment.

The method of Network troubleshooting

Order from bottom to top

Physical layer failure: network cable problem, network card problem. Check whether the packets sent and received by the network connection are normal

Data link failure: 1. Network speed matching is inconsistent, for example, if the adaptive rate is not set in the operating system, it is forced to 10m but the switch or router is forced to 100m. 2.MAC address conflict, someone modified the MAC address in the operating system for various reasons, resulting in address conflict. 3.ADSL is not connected to the Internet. In the case of physical troubleshooting, check whether the fee is in arrears and whether the username password is correct.

Network layer failures: IP address setting error, gateway error, subnet mask error, routing error

Application layer failures: application problems, operating system problems. Methods: reinstall (drive), restart (system or network card), format (system).

Replacement is a method of troubleshooting that can be used frequently.

Understanding OSI model from a security point of view

Physical layer security: prevent random insertion of network cables, random unplugging of power supply, and random movement of physical equipment.

Data link layer security: manage wireless passwords, MAC addresses, and ADSL dialing

Network layer security: IP sealing, port sealing, packet filtering based on IP address

Transport layer security: mainly link security

Application layer security: fix the vulnerabilities of each application in a timely manner

Network equipment

1. Network cable: commonly used twisted pair, 8 pairs of 4 pairs, 10m and 100m twisted pair 1, 3, 4, 6, 1000m all

two。 Nic: MAC physical address, which cannot be changed (except in the operating system, in this case, a physical change), 48-bit binary. Only in the world, the first 24 represent the manufacturer, and the last 24 are designated by the manufacturer.

3. Hub (HUB): is a collision domain, insecure, all connected computers share bandwidth, up to about 30 computers connected.

4. Bridge: can construct MAC address table, forward data based on MAC address, and divide collision domain.

5. Switch: upgraded version of the bridge (multi-port bridge), can store and forward in case of conflict, security, can forward broadcast packets, the bandwidth of each port is exclusive.

6. Router: there is a wide area network interface that can forward data between different network segments and isolate broadcast packets.

According to OSI reference model, network devices can be divided into physical layer devices, data link layer devices and network layer devices.

Data encapsulation process

Computer applications generate data (application layer data)-- > transport layer data segment TCP header + application layer data-> network layer packet IP header + transport layer data segment-> data link layer data frame MAC header + network layer packet + FCS (data check code)-- > physical layer electrical signal 010010101010011

Transmission mode

Simplex: can only be sent or received

Half duplex: can be sent or received, but not at the same time

Full duplex: can send and receive at the same time

Three-layer model of CISCO networking

Access layer

Convergence layer

Core layer

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