Day 10 网络基础

Day 9复习

OSI七层协议口诀：应表会传网数物

协议

应用层

HTTP

HTTPS

FTP

传输层

TCP（文字，图片）

UDP（视频）

网络层

IP

ICMP

一网络设备

Hub 集线器

Hubs connect multiple computer networking devices together. A hub also acts as a repeater in that it amplifies signals that deteriorate after traveling long distances over connecting cables. A hub is the simplest in the family of network connecting devices because it connects LAN components with identical protocols. A hub can be used with both digital and analog data, provided its settings have been configured to prepare for the formatting of the incoming data. For example, if the incoming data is in digital format, the hub must pass it on as packets; however, if the incoming data is analog, then the hub passes it on in signal form. Hubs do not perform packet filtering or addressing functions; they just send data packets to all connected devices. Hubs operate at the Physical layer of the Open Systems Interconnection (OSI) model. There are two types of hubs: simple and multiple port.

集线器将多个计算机网络设备连接在一起。集线器还可以用作中继器，因为它可以放大在连接电缆上长距离传输后劣化的信号。集线器是网络连接设备家族中最简单的，因为它以相同的协议连接LAN组件。集线器可以与数字和模拟数据一起使用，只要它的设置已配置为准备传入数据的格式即可。例如，如果传入数据为数字格式，则集线器必须将其作为数据包传递；但是，如果输入的数据是模拟数据，则集线器将其以信号形式传递。集线器不执行数据包过滤或寻址功能。他们只是将数据包发送到所有连接的设备。集线器在开放系统互连（OSI）模型的物理层上运行。集线器有两种：简单端口和多端口。

Switch 交换机

Switches generally have a more intelligent role than hubs. A switch is a multiport device that improves network efficiency. The switch maintains limited routing information about nodes in the internal network, and it allows connections to systems like hubs or routers. Strands of LANs are usually connected using switches. Generally, switches can read the hardware addresses of incoming packets to transmit them to the appropriate destination. Using switches improves network efficiency over hubs or routers because of the virtual circuit capability. Switches also improve network security because the virtual circuits are more difficult to examine with network monitors. You can think of a switch as a device that has some of the best capabilities of routers and hubs combined. A switch can work at either the Data Link layer or the Network layer of the OSI model. A multilayer switch is one that can operate at both layers, which means that it can operate as both a switch and a router. A multilayer switch is a high-performance device that supports the same routing protocols as routers. Switches can be subject to distributed denial of service (DDoS) attacks; flood guards are used to prevent malicious traffic from bringing the switch to a halt. Switch port security is important so be sure to secure switches: Disable all unused ports and use DHCP snooping, ARP inspection and MAC address filtering.

交换机通常比集线器更智能。交换机是一种提高网络效率的多端口设备。交换机维护有关内部网络中节点的有限路由信息，并且允许连接到集线器或路由器之类的系统。局域网的子线通常使用交换机连接。通常，交换机可以读取传入数据包的硬件地址，以将其传输到适当的目的地。由于具有虚拟电路功能，使用交换机可提高集线器或路由器的网络效率。交换机还提高了网络安全性，因为虚拟电路更难通过网络监视器进行检查。您可以将交换机视为具有路由器和集线器最佳功能的设备。交换机可以在OSI模型的数据链路层或网络层工作。多层交换机是可以同时在两层上运行的多层交换机，这意味着它可以同时充当交换机和路由器。多层交换机是一种高性能设备，支持与路由器相同的路由协议。交换机可能会遭受分布式拒绝服务（DDoS）攻击；泛洪防护用于防止恶意流量使交换机停止运行。交换机端口安全性很重要，因此请确保交换机安全：禁用所有未使用的端口，并使用DHCP侦听，ARP检查和 MAC地址过滤。

Router 路由器

Routers help transmit packets to their destinations by charting a path through the sea of interconnected networking devices using different network topologies. Routers are intelligent devices, and they store information about the networks they’re connected to. Most routers can be configured to operate as packet-filtering firewalls and use access control lists (ACLs). Routers, in conjunction with a channel service unit/data service unit (CSU/DSU), are also used to translate from LAN framing to WAN framing. This is needed because LANs and WANs use different network protocols. Such routers are known as border routers. They serve as the outside connection of a LAN to a WAN, and they operate at the border of your network. Router are also used to divide internal networks into two or more subnetworks. Routers can also be connected internally to other routers, creating zones that operate independently. Routers establish communication by maintaining tables about destinations and local connections. A router contains information about the systems connected to it and where to send requests if the destination isn’t known. Routers usually communicate routing and other information using one of three standard protocols: Routing Information Protocol (RIP), Border Gateway Protocol (BGP) or Open Shortest Path First (OSPF). Routers are your first line of defense, and they must be configured to pass only traffic that is authorized by network administrators. The routes themselves can be configured as static or dynamic. If they are static, they can only be configured manually and stay that way until changed. If they are dynamic, they learn of other routers around them and use information about those routers to build their routing tables. Routers are general-purpose devices that interconnect two or more heterogeneous networks. They are usually dedicated to special-purpose computers, with separate input and output network interfaces for each connected network. Because routers and gateways are the backbone of large computer networks like the internet, they have special features that give them the flexibility and the ability to cope with varying network addressing schemes and frame sizes through segmentation of big packets into smaller sizes that fit the new network components. Each router interface has its own Address Resolution Protocol (ARP) module, its own LAN address (network card address) and its own Internet Protocol (IP) address. The router, with the help of a routing table, has knowledge of routes a packet could take from its source to its destination. The routing table, like in the bridge and switch, grows dynamically. Upon receipt of a packet, the router removes the packet headers and trailers and analyzes the IP header by determining the source and destination addresses and data type, and noting the arrival time. It also updates the router table with new addresses not already in the table. The IP header and arrival time information is entered in the routing table. Routers normally work at the Network layer of the OSI model.

路由器通过绘制使用不同网络拓扑的互连网络设备的大海路径来帮助将数据包传输到目的地。路由器是智能设备，它们存储有关所连接网络的信息。可以将大多数路由器配置为充当数据包筛选防火墙，并使用访问控制列表（ACL）。路由器与通道服务单元/数据服务单元（CSU / DSU）结合使用，还可用于从 LAN框架转换为WAN框架。这是必需的，因为LAN和WAN使用不同的网络协议。这种路由器称为边界路由器。它们充当LAN与WAN的外部连接，并且在网络边界运行。路由器还用于将内部网络划分为两个或多个子网。路由器也可以在内部连接到其他路由器，从而创建独立运行的区域。路由器通过维护有关目的地和本地连接的表来建立通信。路由器包含有关与其连接的系统以及目的地未知的情况下向何处发送请求的信息。路由器通常使用三种标准协议之一传递路由和其他信息：路由信息协议（RIP），边界网关协议（BGP）或开放式最短路径优先（OSPF）。路由器是您的第一道防线，必须将其配置为仅通过网络管理员授权的流量。路由本身可以配置为静态或动态。如果它们是静态的，则只能手动配置它们，并保持这种状态直到更改。如果它们是动态的，他们将了解周围的其他路由器，并使用有关这些路由器的信息来构建其路由表。路由器是将两个或多个异构网络互连的通用设备。它们通常专用于专用计算机，每个连接的网络都有单独的输入和输出网络接口。由于路由器和网关是诸如互联网之类的大型计算机网络的骨干，因此它们具有特殊的功能，这些功能使它们具有灵活性，并能够通过将大数据包分割成适合新网络的较小尺寸来应对变化的网络寻址方案和帧大小。组件。每个路由器接口都有自己的地址解析协议（ARP）模块，自己的LAN地址（网卡地址）和自己的Internet协议（IP）地址。路由器借助路由表，了解数据包可能从其源到目的地的路由。路由表，就像在桥和交换机中一样，是动态增长的。接收到数据包后，路由器将删除数据包标头和标头，并通过确定源地址和目标地址以及数据类型并记录到达时间来分析IP标头。它还使用表中尚未存在的新地址来更新路由器表。IP标头和到达时间信息输入到路由表中。路由器通常在OSI模型的网络层工作。IP标头和到达时间信息输入到路由表中。路由器通常在OSI模型的网络层工作。IP标头和到达时间信息输入到路由表中。路由器通常在OSI模型的网络层工作。

Bridge 网桥

Bridges are used to connect two or more hosts or network segments together. The basic role of bridges in network architecture is storing and forwarding frames between the different segments that the bridge connects. They use hardware Media Access Control (MAC) addresses for transferring frames. By looking at the MAC address of the devices connected to each segment, bridges can forward the data or block it from crossing. Bridges can also be used to connect two physical LANs into a larger logical LAN. Bridges work only at the Physical and Data Link layers of the OSI model. Bridges are used to divide larger networks into smaller sections by sitting between two physical network segments and managing the flow of data between the two. Bridges are like hubs in many respects, including the fact that they connect LAN components with identical protocols. However, bridges filter incoming data packets, known as frames, for addresses before they are forwarded. As it filters the data packets, the bridge makes no modifications to the format or content of the incoming data. The bridge filters and forwards frames on the network with the help of a dynamic bridge table. The bridge table, which is initially empty, maintains the LAN addresses for each computer in the LAN and the addresses of each bridge interface that connects the LAN to other LANs. Bridges, like hubs, can be either simple or multiple port. Bridges have mostly fallen out of favor in recent years and have been replaced by switches, which offer more functionality. In fact, switches are sometimes referred to as “multiport bridges” because of how they operate. 网桥用于将两个或多个主机或网段连接在一起。网桥在网络体系结构中的基本作用是在网桥连接的不同段之间存储和转发帧。他们使用硬件媒体访问控制（MAC）地址来传输帧。通过查看连接到每个网段的设备的MAC地址，网桥可以转发数据或阻止其交叉。网桥还可以用于将两个物理LAN连接到更大的逻辑 LAN。网桥仅在OSI模型的“物理”和“数据链路”层工作。通过将网桥放置在两个物理网段之间并管理两者之间的数据流，可以将较大的网络划分为较小的部分。在许多方面，网桥就像集线器，包括以相同协议连接LAN组件的事实。但是，网桥会在转发前过滤输入数据包（称为帧）的地址。桥接器在过滤数据包时，不会对传入数据的格式或内容进行任何修改。桥接器借助动态桥接表过滤并转发网络上的帧。桥表最初是空的，它维护LAN中每台计算机的LAN地址以及将LAN连接到其他LAN的每个桥接口的地址。像集线器一样，网桥可以是简单端口，也可以是多个端口。近年来，桥大多已不受欢迎，并已被提供更多功能的交换机所取代。实际上，由于开关的操作方式，有时有时将其称为“多端口桥”。

Gateway 网关

Gateways normally work at the Transport and Session layers of the OSI model. At the Transport layer and above, there are numerous protocols and standards from different vendors; gateways are used to deal with them. Gateways provide translation between networking technologies such as Open System Interconnection (OSI) and Transmission Control Protocol/Internet Protocol (TCP/IP). Because of this, gateways connect two or more autonomous networks, each with its own routing algorithms, protocols, topology, domain name service, and network administration procedures and policies. Gateways perform all of the functions of routers and more. In fact, a router with added translation functionality is a gateway. The function that does the translation between different network technologies is called a protocol converter.

网关通常在OSI模型的传输和会话层工作。在传输层及更高层，有许多来自不同供应商的协议和标准。网关用于处理它们。网关提供网络技术之间的转换，例如开放系统互连（OSI）和传输控制协议/ Internet 协议（TCP / IP）。因此，网关连接两个或多个自治网络，每个自治网络都有自己的路由算法，协议，拓扑，域名服务以及网络管理过程和策略。网关执行路由器的所有功能以及更多功能。实际上，具有附加翻译功能的路由器就是网关。在不同网络技术之间进行转换的功能称为协议转换器。

Modem 调制解调器

Modems (modulators-demodulators) are used to transmit digital signals over analog telephone lines. Thus, digital signals are converted by the modem into analog signals of different frequencies and transmitted to a modem at the receiving location. The receiving modem performs the reverse transformation and provides a digital output to a device connected to a modem, usually a computer. The digital data is usually transferred to or from the modem over a serial line through an industry standard interface, RS-232. Many telephone companies offer DSL services, and many cable operators use modems as end terminals for identification and recognition of home and personal users. Modems work on both the Physical and Data Link layers.

调制解调器（调制器-解调器）用于在模拟电话线上传输数字信号。因此，调制解调器将数字信号转换为不同频率的模拟信号，并在接收位置将其发送到调制解调器。接收调制解调器执行反向转换，并向连接到调制解调器的设备（通常是计算机）提供数字输出。通常，通过串行线通过工业标准接口RS-232将数字数据传输到调制解调器或从调制解调器传输数字数据。许多电话公司提供DSL服务，许多电缆运营商使用调制解调器作为终端终端，以识别和识别家庭和个人用户。调制解调器可在物理层和数据链路层上工作。

Repeater 中继器

A repeater is an electronic device that amplifies the signal it receives. You can think of repeater as a device which receives a signal and retransmits it at a higher level or higher power so that the signal can cover longer distances, more than 100 meters for standard LAN cables. Repeaters work on the Physical layer. 中继器是一种电子设备，可以放大接收到的信号。您可以将中继器视为接收信号并以更高电平或更高功率转发信号的设备，以便信号可以覆盖更长的距离，对于标准LAN电缆而言，可以超过100米。中继器在物理层上工作。

Access Point 接入点

While an access point (AP) can technically involve either a wired or wireless connection, it commonly means a wireless device. An AP works at the second OSI layer, the Data Link layer, and it can operate either as a bridge connecting a standard wired network to wireless devices or as a router passing data transmissions from one access point to another. Wireless access points (WAPs) consist of a transmitter and receiver (transceiver) device used to create a wireless LAN (WLAN). Access points typically are separate network devices with a built-in antenna, transmitter and adapter. APs use the wireless infrastructure network mode to provide a connection point between WLANs and a wired Ethernet LAN. They also have several ports, giving you a way to expand the network to support additional clients. Depending on the size of the network, one or more APs might be required to provide full coverage. Additional APs are used to allow access to more wireless clients and to expand the range of the wireless network. Each AP is limited by its transmission range — the distance a client can be from an AP and still obtain a usable signal and data process speed. The actual distance depends on the wireless standard, the obstructions and environmental conditions between the client and the AP. Higher end APs have high-powered antennas, enabling them to extend how far the wireless signal can travel. APs might also provide many ports that can be used to increase the network’s size, firewall capabilities and Dynamic Host Configuration Protocol (DHCP) service. Therefore, we get APs that are a switch, DHCP server, router and firewall. To connect to a wireless AP, you need a service set identifier (SSID) name. 802.11 wireless networks use the SSID to identify all systems belonging to the same network, and client stations must be configured with the SSID to be authenticated to the AP. The AP might broadcast the SSID, allowing all wireless clients in the area to see the AP’s SSID. However, for security reasons, APs can be configured not to broadcast the SSID, which means that an administrator needs to give client systems the SSID instead of allowing it to be discovered automatically. Wireless devices ship with default SSIDs, security settings, channels, passwords and usernames. For security reasons, it is strongly recommended that you change these default settings as soon as possible because many internet sites list the default settings used by manufacturers. Access points can be fat or thin. Fat APs, sometimes still referred to as autonomous APs, need to be manually configured with network and security settings; then they are essentially left alone to serve clients until they can no longer function. Thin APs allow remote configuration using a controller. Since thin clients do not need to be manually configured, they can be easily reconfigured and monitored. Access points can also be controller-based or stand-alone. 虽然接入点（AP）从技术上可以涉及有线或无线连接，但通常指无线设备。AP在第二个OSI层（数据链路层）工作，它既可以充当将标准有线网络连接到无线设备的网桥，也可以充当将数据传输从一个接入点传递到另一个接入点的路由器。类型 IP地址范围 A类 1.0.0.1-127.255.255.254 B类 128.0.0.1-191.255.255.254 C类 192.0.0.1-223.255.255.254 无线接入点（WAP）包括用于创建无线LAN（WLAN）的发送器和接收器（收发器）设备。接入点通常是带有内置天线，发射器和适配器的独立网络设备。AP使用无线基础结构网络模式在WLAN和有线以太网LAN之间提供连接点。它们还具有多个端口，使您可以扩展网络以支持其他客户端。根据网络的大小，可能需要一个或多个AP来提供完整的覆盖范围。附加的AP用于允许访问更多的无线客户端并扩展无线网络的范围。每个AP都受其传输范围的限制-客户端到AP的距离仍然可以获取可用的信号和数据处理速度。实际距离取决于无线标准，客户与AP之间的障碍物和环境条件。高端AP具有高功率天线，从而使它们能够扩展无线信号可以传播的距离。 AP可能还会提供许多端口，这些端口可用于增加网络的大小，防火墙功能和动态主机配置协议（DHCP）服务。因此，我们得到的AP是交换机，DHCP服务器，路由器和防火墙。要连接到无线AP，您需要一个服务集标识符（SSID）名称。802.11无线网络使用SSID来识别属于同一网络的所有系统，并且客户端站必须配置有SSID才能向AP进行身份验证。AP可能会广播SSID，从而使该区域中的所有无线客户端都能看到AP的SSID。但是，出于安全原因，可以将AP配置为不广播SSID，这意味着管理员需要为客户端系统提供SSID，而不是允许其自动被发现。无线设备附带默认的SSID，安全设置，通道，密码和用户名。出于安全原因，强烈建议您尽快更改这些默认设置，因为许多Internet站点都列出了制造商使用的默认设置。接入点可以是胖的或瘦的。胖AP（有时仍称为自治AP）需要通过网络和安全设置进行手动配置。那么他们基本上就任由客户服务，直到他们不再运作为止。瘦AP允许使用控制器进行远程配置。由于不需要手动配置瘦客户端，因此可以轻松地重新配置和监视它们。接入点也可以基于控制器或独立。

4.以下网段中，每个网段的可用主机数是多少？

10.10.0.0——255.255.0.0

256^2-2=65534个

10.0.12.0——255.255.255.0

256-2=254个

172.16.0.0——255.255.0.0

256^2-2=65534个

172.31.200.0——255.255.255.0

256-2=254个

192.168.31.0——255.255.255.0

256-2=254个

192.168.50.0——255.255.255.128

相当于192.168.50.129-192.168.50.254

254-129+1=126个

二网络分类

地理位置

局域网

城域网

广域网

传输介质

有线网

无线网

光纤网

拓扑结构

星型

环形

总线型

树形

通信分类

点对点

广播式

三制作网线流程

网线线序

T568A线序

绿白绿橙白蓝蓝白橙棕白棕

T568B线序

橙白橙绿白蓝蓝白绿棕白棕

交叉线和直通线分别用于什么场景？

交叉线 cross hairs

同种设备之间连接

直通线 straight-through

非同种设备之间连接

四 IP地址

1.IP地址定义与版本

IP地址定义 Internet Protocol Address

是指互联网协议地址，又译为网际协议地址。

IP address stands for internet protocol address; it is an identifying number that is associated with a specific computer or computer network. When connected to the internet, the IP address allows the computers to send and receive information.

2.IP地址分类

公有地址 Public address

私有地址 Private address

3.A、B、C类IP地址的内网IP地址范围

网络类别	内网IP地址范围
A类	10.0.0.0--10.255.255.255
B类	172.16.0.0--172.31.255.255
C类	192.168.0.0--192.168.255.255