vlan5.htm

V-LAN 虚拟局域网的学习笔记

     <td><![endif]>
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     lang=EN-US>0x8100</span></p>
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     <p class=MsoNormal><span lang=EN-US>2Bytes</span></p>
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     <p class=MsoNormal><span lang=EN-US>2Bytes</span></p>
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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"'>内含</span><span lang=EN-US>12bit</span><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>的</span><span lang=EN-US>VLAN</span><span
     style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
     "Times New Roman"'>标识</span></p>
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     <p class=MsoNormal><span lang=EN-US>CRC</span><span style='font-family:
     宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>经过重新计算</span></p>
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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"'>而当数据帧离开汇聚链路时，</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>TPID</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"'>和</span><span lang=EN-US style='mso-bidi-font-size:10.5pt'>TCI</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"'>会被去除，<span style='color:red'>这时还会进行一次</span></span><span
lang=EN-US style='mso-bidi-font-size:10.5pt;color:red'>CRC</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'>的重新计算</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;
color:blue;mso-fareast-language:JA'>TPID</span><span lang=JA 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;mso-fareast-language:JA'>的值，</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'>固定为</span><span lang=EN-US
style='mso-bidi-font-size:10.5pt;color:blue'>0x8100</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"'>。交换机通过</span><span lang=EN-US
style='mso-bidi-font-size:10.5pt'>TPID</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"'>，来确定数据帧内附加了基于</span><span lang=EN-US style='mso-bidi-font-size:
10.5pt'>IEEE802.1Q</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'>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"'>信息。而实质上的</span><span lang=EN-US style='mso-bidi-font-size:
10.5pt'>VLAN ID</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"'>，是</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>TCI</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"'>中的</span><span lang=EN-US style='mso-bidi-font-size:10.5pt'>12</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"'>位元。由于总共有</span><span lang=EN-US
style='mso-bidi-font-size:10.5pt'>12</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"'>位，因此最多<span style='color:blue'>可供识别</span></span><span
lang=EN-US style='mso-bidi-font-size:10.5pt;color:blue'>4096</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'>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"'>。</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"'>基于</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>IEEE802.1Q</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"'>附加的</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"'>信息，就像在传递物品时附加的标签。因此，它也被称作“<span style='color:blue'>标签型</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'>（</span><span lang=EN-US
style='mso-bidi-font-size:10.5pt;color:blue'>Tagging 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'>）</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 lang=EN-US
style='font-size:12.0pt;color:red'>ISL</span></b><span class=GramE><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'>（</span></b></span><b style='mso-bidi-font-weight:normal'><span
lang=EN-US style='font-size:12.0pt;color:red'>Inter Switch Link</span></b><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'>）</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 lang=EN-US style='mso-bidi-font-size:10.5pt'>ISL</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"'>，是</span><span lang=EN-US
style='mso-bidi-font-size:10.5pt'>Cisco</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"'>产品支持的一种与</span><span lang=EN-US style='mso-bidi-font-size:
10.5pt'>IEEE802.1Q</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"'>类似的、用于在汇聚链路上附加</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"'>信息的协议。</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"'>使用</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>ISL</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"'>后，每个数据帧头部都会被附加</span><span lang=EN-US style='mso-bidi-font-size:
10.5pt'>26</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"'>字节的“</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>ISL</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"'>包头（</span><span lang=EN-US style='mso-bidi-font-size:10.5pt'>ISL
Header</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"'>）”，并且<span
class=GramE>在帧尾带上</span>通过对包括</span><span lang=EN-US style='mso-bidi-font-size:
10.5pt'>ISL</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"'>包头在内的整个数据帧进行计算后得到的</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>4</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"'>字节</span><span lang=EN-US style='mso-bidi-font-size:10.5pt'>CRC</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"'>值。</span><span lang=JA
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";mso-fareast-language:JA'>换而言之，就是总共增加了</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt;mso-fareast-language:JA'>30</span><span
lang=JA 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";mso-fareast-language:
JA'>字节的信息。</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"'>在使用</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>ISL</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"'>的环境下，当数据帧离开汇聚链路时，只要简单地去除</span><span lang=EN-US
style='mso-bidi-font-size:10.5pt'>ISL</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"'>包头和新</span><span lang=EN-US style='mso-bidi-font-size:10.5pt'>CRC</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"'>就可以了。由于原先的数据帧及其</span><span
lang=EN-US style='mso-bidi-font-size:10.5pt'>CRC</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"'>都被完整保留，因此无需重新计算</span><span lang=EN-US style='mso-bidi-font-size:
10.5pt'>CRC</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>

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style='mso-spacerun:yes'>&nbsp;</span>SHAPE<span
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     <p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span
     lang=EN-US>ISL<o:p></o:p></span></b></p>
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     <p class=MsoNormal><span lang=EN-US>6Bytes</span></p>
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