📄 vlantheory.htm

📁 BOSON NETSIM是目前最好的路由器模拟软件
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<p><b><span style="font-size: 13.5pt; font-family: Arial; color: green">VLAN 
Theory </span></b></p>
<p>A VLAN is a virtual LAN. VLANs are defined as separate broadcast domains. You 
use VLANs within a switched network to contain broadcasts and segment a 
broadcast domain. VLANs are set up as logical connections and are more flexible 
that physical connections. They act as if they are on the same media but in 
reality they can be on different LAN segments. Because a broadcast domain is 
considered a separate subnet you will still need a router (Layer 3 device) to 
move traffic between subnets. VLANs can be either static or dynamic.</p>
<p><b>VLAN Operations</b></p>
<p>You need to understand how to configure and enable a VLAN, facilitate 
InterVLAN routing in a network containing both switches and routers.</p>
<p><b>Trunking</b></p>
<p>Trunk links are used as point-to-point connections between two switches. This 
could be a connection between a router and a switch, a switch and a server or 
two switches. The trunk speed is either 100Mbps or 1000Mbps (Gigabit Ethernet). 
Without trunk links you would not be able to configure multiple VLANS.</p>
<p>You also need to understand the different trunking protocols, configure 
trunking on a switch and configuring the VLAN trunking protocols.</p>
<p><b>Trunking Protocols</b></p>
<p><b>ISL (Inter-Switch Link) Protocol - </b>ISL is a<i> Cisco proprietary</i> 
protocol used for tagging the source VLAN information on Ethernet trunk 
connections. It uses frame identification by encapsulating each frame between a 
header and the trailer. ISL will add a 26-byte header and a 4-byte trailer to 
the frame. ISL modifies the frame size from 1518 bytes to a new size of 1548 
bytes. <b>(You will be configuring ISL protocol in this lesson.)</b></p>
<p><b>IEEE 802.1Q Protocol</b></p>
<p>802.1Q is a standardized protocol that also is used to maintain VLAN 
information over trunk links. The standardization allows 802.1Q to work with 
different vendors and non Cisco equipment. (ISL only works with Cisco hardware) 
802.1Q protocol does not use encapsulation but embeds its tagging information 
within the Layer 2 frame. The original frame is modified by placing a 4-byte Tag 
Protocol Identifier (TPID) and a 2 byte Tag Control Information (TCI) into the 
existing fields. The size of the frame stays at 1518 bytes.</p>
<p><b>Switches - </b>Remember switches are Layer 2 devices that work at the Data 
Link layer in the OSI model to contain collisions domains. VLANS are used on a 
bridged or switched network to breakup multiple broadcast domains.</p>
<p><b>Routers - </b>Remember routers are Layer 3 devices that work at the 
Network layer in the OSI model to manage broadcast domains because they are on 
separate subnets.</p>
<p><b>Commands - </b>You need to understand what command format is used on each 
Cisco Switch, either CLI or Set-Based CLI</p>
<p><b>IOS CLI </b>(command-line interface)
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