> [TOC]

# 1、网络层与链路层的功能

## 1.1、网络层功能（主要关注性能）

![image-20220820124110410](assets/image-20220820124110410.png)

## 1.2、数据链路层功能

![image-20220820124137359](assets/image-20220820124137359.png)

## 1.3、多播：广播与组播

![image-20220820124240241](assets/image-20220820124240241.png)

# 2、IPv4 分类地址

## 2.1、定义

![image-20220820125012282](assets/image-20220820125012282.png)

## 2.2、IP 地址的分配机构

![image-20220820125159983](assets/image-20220820125159983.png)

![image-20220820125239948](assets/image-20220820125239948.png)

* 网络地址：内网局域网

## 2.3、分类 IP 地址的优点

![image-20220820130044875](assets/image-20220820130044875.png)

## 2.4、分类 IP 寻址的问题

![image-20220820130102805](assets/image-20220820130102805.png)

# 3、CIDR无分类地址

## 3.1、定义

![image-20220820130152762](assets/image-20220820130152762.png)

## 3.2、CIDR 子网划分示例

![image-20220820130442476](assets/image-20220820130442476.png)

![image-20220820130638652](assets/image-20220820130638652.png)

## 3.3、特殊IP地址含义

![image-20220820130718586](assets/image-20220820130718586.png)

![image-20220820130924395](assets/image-20220820130924395.png)

# 4、IP 地址与链路地址的转换：ARP与RARP协议

## 4.1、MAC地址

![image-20220820131601143](assets/image-20220820131601143.png)

## 4.2、2.5 层协议 ARP：从IP 地址寻找MAC地址

![image-20220820131644588](assets/image-20220820131644588.png)

![image-20220820131745021](assets/image-20220820131745021.png)

* 本地缓存MAC-IP对应关系
* 提高效率

## 4.3、ARP 报文格式

![image-20220820132002062](assets/image-20220820132002062.png)

![image-20220820132023700](assets/image-20220820132023700.png)

## 4.4、2.5 层协议 RARP：从MAC 地址中寻找IP地址

![image-20220820132126848](assets/image-20220820132126848.png)

![image-20220820132143803](assets/image-20220820132143803.png)

## 4.5、RARP 报文格式

![image-20220820132158621](assets/image-20220820132158621.png)

## 4.6、ARP 欺骗

![image-20220820132214443](assets/image-20220820132214443.png)

# 5、NAT 地址转换与LVS 负载均衡

## 5.1、IPv4 地址短缺

![image-20220820132340919](assets/image-20220820132340919.png)

![image-20220820132350207](assets/image-20220820132350207.png)

## 5.2、NAT（IP Network Address Translator）应用的前提

![image-20220820132912557](assets/image-20220820132912557.png)

## 5.3、单向（向外）转换NAT：动态映射

![image-20220820132931581](assets/image-20220820132931581.png)

## 5.4、NAPT 端口映射：Network Address Port Translation

![image-20220820133701137](assets/image-20220820133701137.png)

* 与传输层有关：TCP协议

## 5.5、双向（向内）NAT：IP 地址静态映射

![image-20220820153141645](assets/image-20220820153141645.png)

* 没有端口映射
* ip地址经常变化

## 5.6、NAT 优点

![image-20220820153329582](assets/image-20220820153329582.png)

# 6、IP 选路协议

## 6.1、如何传输 IP 报文？

![image-20220820153424313](assets/image-20220820153424313.png)

## 6.2、路由表

![image-20220820153537454](assets/image-20220820153537454.png)

## 6.3、RIP

![image-20220820153618032](assets/image-20220820153618032.png)

## 6.4、OSPF 内部选路协议

![image-20220820153708433](assets/image-20220820153708433.png)

![image-20220820153959540](assets/image-20220820153959540.png)

## 6.5、BGP

![image-20220820154017642](assets/image-20220820154017642.png)

# 7、MTU 与 IP 报文分片

## 7.1、IP报文格式

![image-20220820154237558](assets/image-20220820154237558.png)

## 7.2、MTU

![image-20220820154449223](assets/image-20220820154449223.png)

![image-20220820154540744](assets/image-20220820154540744.png)

## 7.3、避免报文分片

![image-20220820154600158](assets/image-20220820154600158.png)

![image-20220820154626896](assets/image-20220820154626896.png)

# 8、IP 协议的助手：ICMP 协议

## 8.1、定义

![image-20220820154928355](assets/image-20220820154928355.png)

## 8.2、ICMP协议格式

![image-20220820154944959](assets/image-20220820154944959.png)

## 8.3、ICMPv4 报文类型

![image-20220820155038191](assets/image-20220820155038191.png)

![image-20220820155047144](assets/image-20220820155047144.png)

![image-20220820155058439](assets/image-20220820155058439.png)

![image-20220820155108037](assets/image-20220820155108037.png)

# 9、多播与 IGMP 协议

## 9.1、广播与组播

![image-20220820155259241](assets/image-20220820155259241.png)

## 9.2、广播地址

![image-20220820155310951](assets/image-20220820155310951.png)

## 9.3、组播IP地址

![image-20220820155326991](assets/image-20220820155326991.png)

![image-20220820155340804](assets/image-20220820155340804.png)

* 以太网地址：MAC地址

## 9.4、IGMP

![image-20220820155511338](assets/image-20220820155511338.png)

* 路由器知道组和组里面的IP

![image-20220820155722144](assets/image-20220820155722144.png)

![image-20220820155728454](assets/image-20220820155728454.png)