目录
Connection mode of computer
coaxial cable
characteristic：Half-duplex communication，easy-conflict，not secure，中间断了，整个瘫痪
Hub
characteristic：Half-duplex communication，easy-conflict，not secure
Bridge
characteristic：The MAC address of each interface can be learned by self-learning to isolate conflict domains
Switch
characteristic：It's like a bridge with more interfaces，Full-Duplex Communication，secure
Router
- direct network cable，coaxial cable，Hub，bridge，switch，the connected devices who use them must be on the same network segment and in the same broadcast domain.
characteristic：Data can be forwarded on different network segments，Isolated broadcast domain
MAC地址
- Each NIC has a six-byte (48-bit) MAC address
- Unique in the world, solidified in the ROM of the NIC, by the IEEE802 standard
- First three bytes: OUI (Organization Unique Identifier), which is assigned to the vendor by the registrar of IEEE
- Last three bytes: allocated by the vendor
MAC地址的表示格式
ＭＡＣ地址操作
ARP协议获得MAC地址
Two machines need IP addresses and MAC addresses to communicate with each other，如下：
如果一开始两台机器没有在命令行中进行ping操作，是无法进行ICMP的，因为缺少MAC。
此时发送请求的机器就会进行ARP协议发送广播给所有连接的设备，告诉那些设备要寻找MAC的ip地址
FFFF.FFFF.FFF就是广播，在计算机中是一堆1。
然后所有的设备进行检查，当一个设备发现寻找的ip地址就是自己时，就会将MAC返回到原来的机器。
这样，有ip又有MAC，之后就可以进行ICMP协议ping通
ＩＰ地址
A类地址
B类地址
C类地址
子网掩码的CIDR表示方法
子网
为什么要进行子网划分？
等长子网划分：等分成两个子网段做例子
边长子网划分：
