vlan4.htm

V-LAN 虚拟局域网的学习笔记

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     <p class=MsoNormal><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
     mso-hansi-font-family:"Times New Roman"'>每增加一个</span><span lang=EN-US>VLAN</span><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
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<p class=MsoNormal><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>但是，这个办法从<span
style='color:red'>扩展性和管理效率来看都不好</span>。例如，在现有网络基础上再新建</span><span lang=EN-US
style='mso-bidi-font-size:10.5pt'>VLAN</span><span style='mso-bidi-font-size:
10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>时，为了让这个</span><span lang=EN-US style='mso-bidi-font-size:
10.5pt'>VLAN</span><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>能够互通，就需要在交换机间连接新的网线。建筑物楼层间的纵向布线是比较麻烦的，一般不能由基层管理人员随意进行。并且，</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>VLAN</span><span style='mso-bidi-font-size:
10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>越多，楼层间（严格地说是交换机间）互联所需的端口也越来越多，交换机端口的利用效率低是对资源的一种浪费、也限制了网络的扩展。</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'><o:p></o:p></span></p>

<p class=MsoNormal><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>为了避免这种低效率的连接方式，人们想办法让<span
style='color:blue'>交换机间互联的网线集中到一根上，这时使用的就是汇聚链接（</span></span><span lang=EN-US
style='mso-bidi-font-size:10.5pt;color:blue'>Trunk Link</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman";color:blue'>）</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>。</span><span lang=EN-US
style='mso-bidi-font-size:10.5pt'><o:p></o:p></span></p>

<p class=MsoNormal><span lang=EN-US style='mso-bidi-font-size:10.5pt'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span
style='font-size:12.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman";color:red'>何谓汇聚链接？</span></b><b
style='mso-bidi-font-weight:normal'><span lang=EN-US style='font-size:12.0pt;
color:red'><o:p></o:p></span></b></p>

<p class=MsoNormal><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>汇聚链接（</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>Trunk Link</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>）指的是<span style='color:blue'>能够转发多个不同</span></span><span
lang=EN-US style='mso-bidi-font-size:10.5pt;color:blue'>VLAN</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman";color:blue'>的通信的端口</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>。</span><span lang=EN-US
style='mso-bidi-font-size:10.5pt'><o:p></o:p></span></p>

<p class=MsoNormal><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
color:blue'>汇聚链路上流通的数据帧，都被附加了用于识别分属于哪个</span><span lang=EN-US style='mso-bidi-font-size:
10.5pt;color:blue'>VLAN</span><span style='mso-bidi-font-size:10.5pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman";color:blue'>的特殊信息</span><span style='mso-bidi-font-size:10.5pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>。</span><span lang=EN-US style='mso-bidi-font-size:10.5pt'><o:p></o:p></span></p>

<p class=MsoNormal><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>现在再让我们回过头来考虑一下刚才那个网络如果采用汇聚链路又会如何呢？用户只需要简单地将交换机间互联的端口设定为汇聚链接就可以了。<span
style='color:red'>这时使用的网线还是普通的</span></span><span lang=EN-US style='mso-bidi-font-size:
10.5pt;color:red'>UTP</span><span style='mso-bidi-font-size:10.5pt;font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
color:red'>线</span><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>，而不是什么其他的特殊布线。图例中是交换机间互联，因此需要用交叉线来连接。</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'><o:p></o:p></span></p>

<p class=MsoNormal><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>接下来，让我们具体看看汇聚链接是如何实现跨越交换机间的</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>VLAN</span><span style='mso-bidi-font-size:
10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>的。</span><span lang=EN-US style='mso-bidi-font-size:10.5pt'><o:p></o:p></span></p>

<p class=MsoNormal><span lang=EN-US style='mso-bidi-font-size:10.5pt'>A</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>发送的数据帧<span style='color:blue'>从交换机</span></span><span
lang=EN-US style='mso-bidi-font-size:10.5pt;color:blue'>1</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman";color:blue'>经过汇聚链路到达交换机</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt;color:blue'>2</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman";color:blue'>时，在数据帧上附加了表示属于红色</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt;color:blue'>VLAN</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman";color:blue'>的标记</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>。</span><span lang=EN-US
style='mso-bidi-font-size:10.5pt'><o:p></o:p></span></p>

<p class=MsoNormal><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
color:blue'>交换机</span><span lang=EN-US style='mso-bidi-font-size:10.5pt;
color:blue'>2</span><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
color:blue'>收到数据帧后，经过检查</span><span lang=EN-US style='mso-bidi-font-size:10.5pt;
color:blue'>VLAN</span><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
color:blue'>标识发现这个数据帧是属于红色</span><span lang=EN-US style='mso-bidi-font-size:
10.5pt;color:blue'>VLAN</span><span style='mso-bidi-font-size:10.5pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman";color:blue'>的，因此去除标记后根据需要将复原的数据帧只转发给其他属于红色</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt;color:blue'>VLAN</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman";color:blue'>的端口</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>。这时的转送，是指经过确认目标</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>MAC</span><span style='mso-bidi-font-size:
10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>地址并与</span><span lang=EN-US style='mso-bidi-font-size:10.5pt'>MAC</span><span
style='mso-bidi-font-size:10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>地址列表比对后只转发<span class=GramE>给目标</span></span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>MAC</span><span style='mso-bidi-font-size:
10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>地址所连的端口。只有当数据帧是一个广播帧、多播<span class=GramE>帧</span>或是目标不明<span
class=GramE>的帧时</span>，它才会被转发到所有属于红色</span><span lang=EN-US style='mso-bidi-font-size:
10.5pt'>VLAN</span><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>的端口。</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'><o:p></o:p></span></p>

<p class=MsoNormal><span style='mso-bidi-font-size:10.5pt;font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>蓝色</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>VLAN</span><span style='mso-bidi-font-size:
10.5pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>发送数据帧时的情形也与此相同。</span><span lang=EN-US style='mso-bidi-font-size:
10.5pt'><o:p></o:p></span></p>

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