Network protocols and management

OSI model

Overview

OSI model is a standard model specified by the International Organization for Standardization, a total of seven

Layered concept

Application layer (Application)
- Network Access application layer process
  - For the application process (eg: e-mail, file transfer and terminal emulation) to provide network services
  - Provide user authentication
The presentation layer (the Presentation)
- Data representation
  - Ensure that the receiving system can read data
  - Formatted data
  - Building data
  - Negotiation for data transfer syntax for the application layer
  - Provides encryption
Session layer (Session)
- Inter-host communication
  - Build, manage and terminate sessions between applications
Transport Layer (Transport)
- Transmission problems
  - To ensure the reliability of data
  - Establish, maintain and terminate virtual circuits
  - Through error detection and recovery
  - Information flow control to guarantee reliability
Network layer (Network)
- data transmission
  - Routing data packets
  - Choose the best path to transfer data
  - Logical addressing and routing support
Data Link Layer (Data Link)
- Media access
  - How to define the data format for transmission and how to control access to the network
  - Support for error detection
The physical layer (the Physical)
- Binary transfer
  - Close to initiate and maintain the physical link specification defines the electrical, mechanical specifications, process specifications, functional specifications, and

Data encapsulation and decapsulation

Layer by layer on a fallen package
Data re-opened

Data re-opened

PDU

PDU: Protocol Data Unit, refers to a protocol data unit is a data unit transferred between peer level

PDU is the physical layer data bit bit
PDU data link layer frame is a data frame
PDU is a data packet network layer packet
PDU is the transport layer data segment segment
Other higher-level PDU message is the message

General communication mode

Communication mode is generally divided into three types:

Unicast
Multicast
Broadcast
one-way and two-way transmission:
Simplex: transmission only in one direction
Half-duplex: the same time can only transmit in one direction
Full duplex: transmission in both directions at the same time

LAN standards

Shielded twisted pair cable

Unshielded twisted pair UTP, which is usually referred to as cable interface RJ-45 connector, a mode T568A, T568B lines of two components, generally T568B connected to the computer, divided into straight and crossover cable

LAN standards schematic

LAN

Ethernet Frame以太网帧结构

Frame
以太网帧有两个版本，现在用蓝色的版本，有8字节的先导头，6字节的目的地址，6字节的源地址，2字节的上层协议类型，46-1500字节的数据，4字节的校验位，由于到达电脑的都是已经被验证过正确的包，所以抓包到的没有先导头和校验位

MAC地址

MACADDR
其中前一半是分配给厂商的，后一半是厂商分配的
MACADDRESS

各种网络设备

Hub集线器

仅仅是将插入接口的网络设备将他们连起来，工作特点：

共享带宽
半双工

以太网桥
以太网桥工作原理：
以太网桥监听数据帧中源MAC地址，学习MAC，建立MAC表 * 对于未知MAC地址，网桥将转发到除接收该帧的端口之外的所有端口
当网桥接到一个数据帧时，如果该帧的目的位于接收端口所在网段上，它就过
滤掉该数据帧；如果目的MAC地址在位于另外一个端口，网桥就将该帧转发到
该端口
当网桥接到广播帧时候，它立即转发到除接收端口之外的所有其他端口

交换式以太网的又是：

扩展了网络带宽
分割了网络冲突域，使网络冲突被限制在最小的范围内
交换机作为更加智能的交换设备，能够提供更多用户所要求的功能

交换机

交换机每一个接口对应一个设备，在学习之后，就会对应转发，将数据包转化到对应的端口，学习过程是根据发送的端口和MAC地址对应来记忆端口
特点：

隔断冲突域
每个端口一个带宽，不会带宽共享

Router路由器

路由器的作用：

分隔广播域
选择路由表中到达目标最好的路径
维护和检查路由信息
连接广域网

路由：把一个数据包从一个设备发送到不同网络里的另一个设备上去，这些工作依靠路由器来完成。路由器只关心网络的状态和决定网络中的最佳路径，路由的实现依靠路由器中的路由表来完成

VLAN

可以起到分隔广播域的作用，管理跟家灵活，在交换机内对不同的网络设备进行分组，不同的分组之间通信通过路由通信

IEEE 802.1Q帧结构：
VLAN1

VLAN12

VLAN标签各字段含义

TPID: Tag Protocol Identifier (Tag Protocol Identifier), 2Byte, frame type, a value of
0x8100 indicates when the IEEE 802.1Q VLAN frames. If the device does not support 802.1Q receives such a frame
will be discarded, each vendor can define the value from the field. When the neighbor device configured as a non TPID value
when 0x8100, to be able to identify such packets, to achieve interoperability, the TPID value must be modified in the device, and to ensure
and TPID values of neighboring devices configured with the same
PRI: Priority, 3bit, indicating frame 802.1p (extended protocol is IEEE 802.1Q) priority. It takes
a value ranging from 0 to 7, the greater the value the higher the priority. When the network is congested, switches preferentially transmit high priority data frame
CFI: Canonical Format Indicator (standard format indicator bits), 1bit, represents a different MAC address
whether a transmission format encapsulated in the standard medium for compatibility Ethernet and Token Ring networks. CFI value of 0 indicates that
the MAC address encapsulated in the standard format, is encapsulated in a non-standard format represents. In Ethernet, CFI value 0 * VID: VLAN ID, 12bit , indicating that the data frame belongs VLAN ID. VLAN ID ranges from 0 to
4095. Since the value 0 Reserved 4095 and the protocol, the valid range for the VLAN ID is 1 to 4094

11-1 network protocols and management