CCNA快速学习–笔记整理1（原创） – 作者:test555-安全小百科

Type ofnetwork devices
end devices （host）： clients 客户机、servers 服务器	End devices originate the data that flows through the network 终端设备会发出通过网络传输的数据 End devices are the source or destination of the messages 终端设备是消息的源或目的地 They are the interface between humans and the network 它们是人与通信网络之间的界面
intermediary devices	Connect hosts (end devices) to the network 中间设备可以将单个主机连接到网络中 They direct the path of the data 中间设备可以引导数据路径

Types of Network Media
copper 电缆线 fiber-optic 光纤 wireless 无线	How far the medium can send a signal所选介质可以成功传送信号的距离 Environment where the selected medium is to be installed要安装所选介质的环境 Media costs and installation costs介质成本和安装成本

BANDWIDTH 带宽 is measured in Bits per second ：BANDWIDTH is a measure of the data carrying capacity of the media 带宽是对介质的传送数据能力的一种衡量标准

Type of Network
Peer to Peer 对等网络	Client/Server 客户端/服务器网络
Easy to create 易于创建	Hard to create
Costs less Money 实施成本更少	Costs more Money
No central device is used for administration 缺少集中管理	Servers are used as central devices for administration
通过网络大小划分网络
LAN Local Area Network	Network in a small geographical area 针对较小地理区域内的用户和终端设备提供网络访问的基础设施
WLAN	WIRELESS LAN — Phone、tablets
WAN Wide Area Network	Network over a wide geographical area 针对广泛地理区域内的其他网络提供访问的网络基础设施
通过使用人群划分
INTERNET	Everyone can use
INTRANET 内部网	Company’s network that only it’s employees can use 公司的网络，只有它的员工才能使用
EXTRANET 外联网	Company’s network accessed by suppliers, customers, etc 可对供应商、客户等提供安全访问公司数据的服务

Type of Internet
broadband 带宽		wireless 无线
DSL 电话线拨号上网	cable 同轴电缆	cellular 蜂窝网络	satellite 卫星不适合木质区域

Characteristics of a good network

CONVERGED 融合：多媒体、语音、视频、文本
FAULT TOLERANT 容错：多路径去往目的地
NO CONGESTION 无拥塞：QOS （Quality of Service ）优先选择流量，实时传输语音视频
SECURED 安全

DATA SECURITY

Data CONFIDENTIALITY 保密性：强复杂的密码授权
Data Integrity 完整性：no one can change
Data Availability 可用性：需要时可访问

Security Violation

Denial of services to your resource 资源拒绝服务
virus
Capture of personal data

How to STOP Security Violations ？

Anti-Virus Software – 防毒软件
Firewall – 防火墙
Intrusion Prevention System (IPS) – 入侵防御
Intrusion Detection System (IDS) – 入侵检测

Operating System

Hardware 硬件
kernel 内核
Shell 外壳：用户界面 Command line interface （CLI）：Console，Telnet，secure shell（SSH），AUX

Graphical User interface（GUI）

Cisco IOS 访问方式
Console	console线with Serial Port 串行端口 or USB Port ，计算机使用终端仿真软件	第一次访问新设备必须使用console 默认工作物理设备附近工作
Telnet	非默认工作。远程访问	TELNET <IP Address/Hostname>
Secure Shell SSH	非默认工作。远程访问，SSH encrypts the user ID, password and data of the remote session 加密远程会话	SSH -L <Username> <IP Address/Hostname>
Secure Shell SSH
AUX	旧设备，电话连接访问设备

Types of Modes
Primary 主要命令模式验证排错	User—Exec 用户Exec模式
	Privilege Exec 特权模式
Configuration 配置命令模式	Line 线路配置模式
	Interface 接口配置模式

命名约定

Starts with a letter (a-z) – 以字母开头
Ends with a letter (a-z) or digit (0-9) – 以字母或数字结尾
Contains no spaces – 不包含空格
Use only letters, digits, and dashes – 仅使用字母、数字和破折号
Be less than 64 characters in length – 长度少于 64 个字符

Banner Message 标语

MAC-ADDRESS

Address made of 12 Hexa-Decimal numbers.
Hexa-Decimal is 0-15 (0-9, 10-A, 11-B, 12-C, 13-D, 14-E, 15-F)
One Hexa-Decimal digit is equal to 4 bits.
MAC-Address = 12*4 = 48 bits.
Example of a MAC-Address is: 0090-271A-60AF.
To Check MAC-Address of NIC on you computer,use the command: ipconfig/all

IP Address

子网掩码

Identify number of network bits & host bits in an IP Address

Helps to determine (find) which subnet (network) host belongs

确定主机所属的子网

We can say, 192.168.1.1 belongs to 192.168.1.0/24 network

PING

Check if the destination device is reachable through the network

是否可以通过网络到达目的设备

Tells about the average time to go to the destination & come back

数据包到达目的设备以及响应返回源设备的平均时间

IPV4	32位 4组 8位十进制组成 IP Address is of 32 bits. Network portion + Host portion 网络部分＋主机部分 IP Address has 4 Octets, so 4 numbers (e.g. 10.1.6.250). Each Octet = 8 bits. Smallest number in an IP Address can be a 0. Biggest number in an IP Address can be a 255. 回环地址 127.0.0.1
IPV4过渡IPV6技术	Dual Stack 双堆栈设备同时可以使用 IPv4,IPv6 地址 Tunneling 隧道在IPv4网络中传输 IPv6 包 Translation 转换 Network Address Translation 64 – NAT64 IPv6 packet is translated to an IPv4 packet and vice versa
IPv6	128位 4组 32位 16进制前面的0忽略 :: 连接接口需要Link-Local 地址 IPv4 from 192.254.0.1 — 169.254.255.254
	Types of IPv6 Addresses
	Unicast Address Global Unicast – Like IPv4 Public IP Addresses Global Routing Prefix (Prefix Mask) – Network Bits Subnet ID – Bits that identify different LANs or Subnets Interface ID – Host Bits Unique-Local – Like IPv4 Private IP Addresses Cannot be translated to a Global Unicast address Link-Local (FE80::10) – Automatic IP inside the Local network Cannot be used to send data outside the local network Loopback (::1/128) – Like 127.0.0.1 of IPv4 ping ::1
	Multicast Address
	Anycast Address 用于两台及以上设备 Packet with Destination IP of the Anycast IP is sent to the device nearest to the source 发送至任播地址的数据包会被路由到最近的拥有该地址的设备
	Two ways to assign IPv6 Address
	Static
	Dynamic SLAAC — Stateless Address Autoconfiguration Device gets the IP Configuration from the Router DHCP server is not needed Stateless DHCPv6 = SLAAC + DHCPv6 SLAAC gives IPv6 address, Prefix Mask & DG DHCPv6 gives DNS Server information to the device Stateful DHCPv6 No SLAAC only DHCPv6 DHCPv6 server gives away the full IP Configuration

子网划分

原因：

Slow network operations due to the significant amount of broadcast traffic.网络运行缓慢，原因是它导致的广播流量太大
Slow device operations because a device must accept and process each broadcast packet.设备运行缓慢，原因是设备必须接受和处理每个广播数据包
子网划分可以降低整体网络流量并改善网络性能方便管理员实施安全策略，例如哪些子网允许或不允许进行通信

等长子网划分

非等长子网

私有地址 Private Address	RFC 1918 Internal Address Range	CIDR Prefix
	Class A：10.0.0.0 — 10.255.255.255	10.0.0.0/8
	Class B：172.16.0.0 — 172.31.255.255	172.16.0.0/12
	Class C ：192.168.0.0 — 192.168.255.255	192.168.0.0/16
公有地址 Public Address	除去私有地址

Class A	1.0.0.0 — 126.0.0.0	First number of Class A IP Address is from 1 to 126 Default Subnet Mask for Class A is – 255 . 0 . 0 . 0 Class A IP Address has 8 Network Bits + 24 Host Bits Prefix Mask：/8
Class B	128.0.0.0 — 191.255.255.255	First number of Class B IP Address is from 128 to 191 Default Subnet Mask for Class B is – 255 . 255 . 0 . 0 Class B IP Address has 16 Network Bits + 16 Host Bits Prefix Mask：/16
Class C	192.0.0.0 — 223.255.255.255	First number of Class C IP Address is from 192 to 223 Default Subnet Mask for Class C is – 255 . 255 . 255 . 0 Class C IP Address has 24 Network Bits + 8 Host Bits Prefix Mask：/24

Type of IP Address
Network Address	Network Address is just like Father of the Family It is the First IP Address of the Network Host Bits of the Network Address are all 0’s
Broadcast Address	If you want everyone in the network to listen, send a message to the Broadcast Address Broadcast Address is just like Mother of the Family It is the Last IP Address of the Network Host Bits of the Broadcast Address are all 1’s
Host Addresses	Host Addresses are the Valid IP Addresses 有效IP地址 Valid means that Host IP Addresses can be assigned (given) to the network devices Host Addresses are IP Addresses between the Network Address & the Broadcast Address

Types of Network MESSAGES
Unicast ：单播	one to one
Broadcast ：广播	Limited Broadcast 有线广播 To send Broadcast in the Local (your) network Destination IP Address 255.255.255.255
Broadcast ：广播	Direction Broadcast 方向广播 To send Broadcast to a Remote (outside) network Let’s say if the remote network is 192.168.1.0/24,then Destination IP of Directed Broadcast is the Broadcast Address Destination IP: 192.168.1.255/24
Multicast ：组播	One packet is sent to a group of hosts (devices) Multicast IP range: 224.0.0.0 – 239.255.255.255 Multicast IP range (Local Network): 224.0.0.0 – 224.0.0.255 Used by Routers to exchange routing information 路由器可以使用组播传输交换路由信息

七层协议

All	Application Layer 应用层		HTTP 80,DNS（53） ,DHCP( UDP67和UDP68), FTP/TFTP POP3 110/IMAP,SMTP 25	应用层软件交互，提供网络资源负责决定一个进程的可用性并查看是否有可用的资源分给该进程
People	Presentation Layer 表示层		Html，MP3，MP4，ect	编解码，解压缩，加解密
Seem	Session Layer 会话层		logical Port 21,22,23,80…	创建于发送方和接送方监视数据传输时会话出具传输结束终止会话
To	Transport Layer 传输层	Segment 字段	TCP （可靠有确认）or UDP SPX	将数据分层小部分数据封装成PDU(Protocol data unit) 源和目的 Port Number 添加到字段 flow control
Need	Network Layer 网络层	Packet 数据包	Encapsulate the Transport Layer PDUs从传输层封装 PDU Routing the packets towards their destination将数据包路由到目的地	源和目的IP地址添加到数据段
Data	Data-link Layer 数据链路层	Frame 帧		源和目的MAC地址添加到 packet
Processing	Physical Layer 物理层		NIC (Network interface card or LAN card)	将帧转化为位 BIT（0&1）

Parts of the Frame		Frame Encapsulation / Frame Encoding 帧编码
Header 帧头	Frame start	8 bytes 二进制表示新帧的开始 10101011
	Addressing 编址	6 bytes 目的MAC地址 + 6 bytes 源 MAC地址
	Type 类型	2 bytes 告诉数据包中的三层协议 It is 0X0800 for IPv4 – 0000 1000 0000 0000 It is 0X86DD for IPv6 – 1000 0110 1101 1101 0X means Hexa-Decimal
	Control 控制	4 bytes 3 Bits out of 4 Bytes are used for Quality of Service 4个字节中的3个字节用于服务质量 111 means most important data 101 is used for VOICE Data 100 is used for VIDEO Data
Data 数据		数据完整性Data Integrity 无人能够在数据传输过程中更改数据
Trailer 帧尾	Error Detection 错误检测	4 bytes Frame Check Sequence (FCS) 检查数据完整性 Cyclic Redundancy Check – CRC循环冗余检验 CRC = 比较计算传输前后FH（帧头）+Data+FCS 值
Trailer 帧尾	Frame Stop
Size of Ethernet Frame
Runt 侏儒帧	＜64 bytes	drop
	64 bytes — 1518 bytes
Jumbo 巨人帧	＞ 1518 bytes	drop

	TCP/IP	OSI
4	Application	Application Layer Presentation Layer Session Layer	Data
3	Transport	Transport Layer	Segment 字段
2	Internet	Network Layer	Packet 数据包
1	Network Access	Data-link Layer Physical Layer	Frame 帧

TCP Transmission Control Protocol 传输控制协议	UDP User Datagram Protocol 用户数据报协议
Reliable Protocol Guarantee delivery of data 保证数据的传送	Unreliable Protocol NO guarantee of delivery
High Overhead (Big)，SLOW	Low Overhead (Small), FAST
Connection Oriented 面向连接：（要事先建立一条通信线路，其有三个过程：建立连接、使用连接和释放连接）	Connectionless 面向无连接：（通信双方不需要事先建立一条通信线路，而是把每个带有目的地址的包（报文分组）送到线路上，由系统自主选定路线进行传）
TCP如何避免数据冗余 congestion TCP uses Window Size 窗口大小（SLIDING WINDOW 滑动窗口） Default Window Size is 1
TCP 三次握手 TCP uses a Handshake before starting to send the data TCP uses Control Bits for the handshake Telnet — TCP 23 SSH — TCP 22 FTP —- TCP 21 HTTP — TCP 80
2 characteristics shared by TCP & UDP
Port Numbers 端口号	Ensure communication & connectivity with remote device 以确保与远程网络设备的通信和连接 To send data to the correct application 让接收主机转发数据到适当的应用程序 To deliver the Web page to the correct web browser 确保正确的网页传输到正确的浏览器窗口
Checksum 校验和	Sequence Number 序列号：每一个数据段有一个不同的序列号 Acknowledgement Number 应答 = 序列号 + 1	To reassemble the segments at the remote location 在远程位置重组数据段 To identify missing segments at the destination 确定目的地丢失的数据段

Data Link Sublayers 数据链路子层
Logical Link Control （LLC）逻辑链路控制	为网络层服务 LLC在帧中添加信息该信息用于标识帧中所封装的网络层协议 (IPv4 or IPv6)
Media Access Control （MAC）介质访问控制	帮助在不同类型上发送和接受数据帧同时处理错误检测 Error Detection

Topology 拓扑
LOGICAL Topology 逻辑拓扑	Logical topology shows how the network transfers data between connected devices 逻辑拓扑显示网络在相连节点之间传输数据的方式设备接口连接信息地址
PHYSICAL Topology 物理拓扑	Physical topology shows physical connection of devices 物理拓扑显示设备的物理互连方式设备位置
Types of LAN Topologies
Star 星型
Extended Star 拓展星型	2 or more Star Topologies connected together 中心设备相连
Bus 总线	All devices are connected in a line & ends terminated 所有终端设备都相互连接，并在两端以某种形式端接
Ring 环	All devices are connected like a ring (no termination) 终端系统与其各自的邻居相连，形成一个环状。与总线拓扑不同，环拓扑不需要端接。
Types of WAN Topologies
Point-to-Point – 点对点
Hub & Spoke – 集中星型	Hub – Head Office Spokes – Branch Offices 星型拓扑的 WAN 版本，在该拓扑中有一个中心站点，使用点对点链路互连各分支站点
Full Mesh – 全网状	所有人直连
Hybrid – 混合	混合拓扑是点对点、集中星型或网状拓扑的变体或组合。这可能包括部分网状或扩展星型拓扑。

Job of Switch & Router
Switch	send data from one end device to another in same LAN
	Learn MAC-address + Port number 学习学习源 MAC地址和帧进入端口号，并且储存到CAM表中（Content Addressable Memory）（Mac address of End Device + Port number to which End Device is connected） Command to CHECK the CAM Table is:# show mac-address-table Command to DELETE the CAM Table is:# clear mac-address-table
	Forward Message 转发如果已经学习目的Mac地址，就发送消息位置如果没有学习过，就会除去传入端口外所有端口转发帧（泛洪） 1.Store and Forward 存储转发交换接受全帧 CRC 检测帧大小，丢弃过大或者过小帧 High Latency 高滞后时间 2.Cut-Through 直通交换不等待全部帧只确认目的MAC地址不检查帧大小 Low Lanterncy
		Router	send data from one end device to another in different LANs
Path Selection – 路径选择
Packet Forwarding – 数据包转发

路由表 Routing Table

Check the Routing Table of the Router：# show ip route

Delete the Routing Table of the Router：# clear ip route *

Computer

#Route Print

#Netstat -r

Types of Communication 传输类型
Simplex 单工	键盘–电脑
Half Duplex 半双工	Both devices can send & receive data but one at a time 不能同时
Full Duplex 全双工	Both devices can send & receive data at the same time

交换机与其他设备直通线，和交换器交叉线

路由器，电脑之间使用交叉线

AUTO-MDIX

自动检测以太网电缆类型的功能

Types of Copper Cables
Unshielded Twisted-Pair (UTP) 非屏蔽双绞线	STRAIGHT-THROUGH – 直通 CROSSOVER – 交叉 ROLLOVER – 全反
Shielded Twisted-Pair (STP) 屏蔽双绞线
Coaxial 同轴电缆

Fiber-optic cable 光纤
Single-Mode Fiber (SMF)单模光纤	One Ray of Light in the Fiber 单束光 Uses LASER as Light Source 激光 Mostly used with Campus Backbone 园区主干
Multi-Mode Fiber (MMF)多模光纤	Multiple Rays of Lights in the Fiber Uses LED as Light Source Mostly used with LANs

copper cable	Less Money Easy to terminate & install Can be installed in places with sharp bends 急转弯 Cannot be used for long distances (<100 metres)
Fiber-optic	More Money Hard to terminate & install Cannot be installed in places with sharp bends Can be used for longer distances
wireless	smartphone & tablets SECURITY – 安全性 INTERFERENCE – 干扰 COVERAGE AREA – 覆盖范围

Throughput 吞吐量

Bits sent across the media over a given period of time

特定时间内通过介质传输的位数

Default Gateway ——DG

It helps a PC to send data outside its LAN

默认网关是可以将流量路由到其他网络的网络设备。它是将流量从本地网络路由出去的路由器。

ARP Request – Address Resolution Protocol

Disadvantages of ARP Request

It is a BROADCAST Message, so it goes to everyone in the same LAN. So everyone on the same LAN has to RECEIVE & PROCESS the ARP Request.本地网络上的每台设备都将收到并处理它们
In low bandwidth networks, data transfer can be delayed because of ARP broadcasts在带宽较低的大型网络中，多个 ARP 广播可能会导致数据通信延迟
Hacker can change the MAC & IP mappings to intercept (get) network data. This is called ARP SPOOFING 欺骗.网络攻击者可能会控制 ARP 消息中的 MAC 地址和 IP 地址映射，以图拦截网络流量

Application Layer Protocols
HTTP	Hyper Text Transfer Protocol 超文本传输协议	GET – Client uses it to request html page from web server PUT – Used to upload content to the web server
DHCP	Dynamic Host Configuration Protocol 动态主机配置协议	request an IP address
DNS	Domain Name Service 域名服务器	Translates Domain Name (URL) to IP Address (vice versa) Windows command to check DNS is > nslookup www.baidu.com

How to build a small Network

Buy Network Devices
Network Design & Cabling
Use of REDUNDANCY in the Network
IP Addressing

- Choose the IPv4 and/or IPv6 addressing
- Plan the IP Addressing Scheme – Do Subnetting规划IP寻址方案
- Assign the IP Addresses

5. Configure common Protocols & Services

6. Manage Network Traffic

Secure the Network

Identify the Types of Network Threats – 威胁
Identify the Types of Network Attacks – 攻击
Monitor – 监控 the network at all times

Types of Attacks
Malware attack 恶意软件攻击	damage 损伤 or steal 盗 data or cause problem in the working of the network TROJAN HORSE – Looks like a Video Game VIRUS – Spreads & copies itself into some other program. It is a .exe file. A user has to install a virus to make it work. WORM – Just like a Virus but you do not need to install it.
Reconnaissance attack 侦查攻击	This type of attack is to gather information that can be used to plan a bigger attack in future 收集未来可用于规划更大攻击的信息
Access attack 访问攻击	It is used to gain unauthorized access to the data以获得未经授权的访问数据 Password attacks & Man in the Middle attacks are examples of Access Attacks Brute Force attacks, Trojan Horse, Packet Sniffers are different types of Password Attacks
	Brute Force attack 暴力攻击 Brute Force attack → Password attack → Access Attack Hacker keeps trying the password many number of times Router(config)# login block-for 180 attempts 4 within 90 This command will block login attempts for 180 seconds if there are four failed login attempts within 90 seconds
		Denial of Service attack 拒绝服务攻击	This attack is used to stop the network users from using a network service, like DHCP, DNS, etc. Short name – DOS Attack