VLAN实验：三层交换原理

Switch#vlan database
    % Warning: It is recommended to configure VLAN from config mode,
      as VLAN database mode is being deprecated. Please consult user
      documentation for configuring VTP/VLAN in config mode.
    Switch(vlan)# vlan 2 name marking
    VLAN 2 added:
        Name: marking
    Switch(vlan)# vlan 3 name counting
    VLAN 3 added:
        Name: counting

2 分配端口
    Switch(config)#interface FastEthernet0/1
    Switch(config-if)#switchport mode access
    Switch(config-if)#switchport access vlan 2
    Switch(config-if)#exit
    Switch(config)#interface FastEthernet0/2
    Switch(config-if)#switchport access vlan 2
    Switch(config-if)#interface FastEthernet0/3
    Switch(config-if)#switchport access vlan 3
    Switch(config-if)#interface FastEthernet0/4
    Switch(config-if)#switchport access vlan 3
    Switch(config-if)#exit
    Switch(config)#exit
    Switch#

    3 Show vlan 查看信息

Switch#show vlan

VLAN Name                             Status    Ports
    ---- -------------------------------- --------- -------------------------------
    1    default                          active    Fa0/5, Fa0/6, Fa0/7, Fa0/8
                                                    Fa0/9, Fa0/10, Fa0/11, Fa0/12
                                                    Fa0/13, Fa0/14, Fa0/15, Fa0/16
                                                    Fa0/17, Fa0/18, Fa0/19, Fa0/20
                                                    Fa0/21, Fa0/22, Fa0/23, Fa0/24
    2    marking                          active    Fa0/1, Fa0/2
    3    counting                         active    Fa0/3, Fa0/4
    1002 fddi-default                     active
    1003 token-ring-default               active
    1004 fddinet-default                  active
    1005 trnet-default                    active

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
    ---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
    1    enet  100001     1500  -      -      -        -    -        0      0
    2    enet  100002     1500  -      -      -        -    -        0      0
    3    enet  100003     1500  -      -      -        -    -        0      0
    1002 enet  101002     1500  -      -      -        -    -        0      0
    1003 enet  101003     1500  -      -      -        -    -        0      0

其实做这个实验很简单就是划分子网，主要是为了说明三层交换机最本质工作原理，即一次路由，多次交换  结合arp的工作原理，两台主机通讯时，传统的2层交换机进行arp广播寻找目标mac地址，，当目的主机在同一网段内时，不需涉及网关。否则由网关回复arp广播。

传统的2层交换模块不能实现网间互访，而三层交互交换机的三层路由模块把源和目的IP地址缓存交换机中，随后第3层中跨子网的包传送将不再由路由器来进行。实验中的三层交换机充当了传统网络中的路由器的角色，通过它可以实现网间互访。