网络基本知识

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OSI模型：物理层；数据链路层；网络层；传输层；会话层；表示层；应用层。
网络地址分类：
A   1-127；
B    128-191；
C    192-223
每个网段中结尾为255：广播地址；
每个网段中结尾为0：网络循环地址；
解析方式：
主机名<-->IP：/etc/host 文件；NIS；DNS
IP<-->MAC地址（六组二十四位八进制数字）：ARP地址解析
TCP：双向确认传输；
UDP：单向传输；
传输介质：双绞线；同轴电缆；光缆
网络拓扑结构：总线型；环型；星型
访问方式：
802.3 / Ethernet：CSMA/CD；
802.4 / 802.5 / FDDI：令牌
分子网：
例子1：128.1.X.X 如果不分网段，可用主机IP为256*256 - 2(广播地址；网络循环地址)  65534，子网掩码：255.255.0.0
为方便管理，需要分子网。取2位分子网。
子网网段分别为：
128.1.00|XXXXXX.X：路由使用
128.1.01|XXXXXX.X：用户使用
128.1.10|XXXXXX.X：用户使用
128.1.11|XXXXXX.X：路由使用
01网段具体IP:
128.1.01000000.0：网络循环地址；
128.1.01111111.255：广播地址；
正常使用地址128.1.01000000.1 -- 128.1.01111111.254 共16382；
子网掩码：255.255.192.0
例子2：128.1.X.X 取4位分子网
子网网段共16(其中头尾为路由所用)个分别为：
128.1.0000|XXXX.X
128.1.0001|XXXX.X
....
128.1.1111|XXXX.X
0001网段具体IP:
128.1.00010000.0：网络循环地址；
128.1.00011111.255：广播地址；
正常使用地址：128.1.00010000.1-- 128.1.00011111.254 共4094；
子网掩码：255.255.240.0
B类和C类子网划分参考表单 
网络基本知识 - thomas_shen - thomas_shen的博客
third level switch vs router
router: NAT + IP forward function; applied in connection of LAN and WAN

third level switch: IP forward function; applied in connection of WAN and WAN

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