Trunking

  • VLANs are local to each switch’s database, and VLAN information is not passed between switches.
  • Trunk links provide VLAN identification for frames traveling between switches.
  • Cisco switches have two Ethernet trunking mechanisms: ISL and IEEE 802.1Q.
  • Certain types of switches can negotiate trunk links.
  • Trunks carry traffic from all VLANs to and from the switch by default but can be configured to carry
    only specified VLAN traffic.
  • Trunk links must be configured to allow trunking on each end of the link.

    To enable trunking between the switches & specify a range of ports use the following steps :

    switchport trunk allowed vlan 1-5
    switchport mode trunk
    switchport nonegotiate
    speed 100
    duplex full
    Now Create the Vlan’s on the Switch :

    vlan database
    vlan 2 name MEDIA
    vlan 3 name DMZ
    vlan 4 name OFFICE
    vlan 5 name ACCOUNTS

    Now exit : This will create a vlan.dat file in flash memory.
    Don’t forget the ” ip default-gateway 192.168.1.1″ command :
    where 192.168.1.1 is the Layer3 Trunking Device.

    Now let create Layer 3 interVLAN Routing :

    Whenever hosts in one VLAN need to communicate with hosts in another VLAN, the traffic
    must be routed between them. This is known as     inter-VLAN routing. On Catalyst switches it is
    accomplished by creating     Layer 3 interfaces (Switch virtual interfaces (SVI) ).

    Verify ip routing is enabled,  Enable routing on the switch by using the ip routing command.

    interface FastEthernet0/1
    description TRUNK_PORT
    no ip address
    speed 100
    full-duplex
    !
    interface FastEthernet0/1.1
    description TRUNK_VLAN 1
    encapsulation dot1Q 1 native
    ip address 192.168.1.1 255.255.255.248
    !
    interface FastEthernet0/1.2
    description MEDIA
    encapsulation dot1Q 2
    ip address 192.168.2.1 255.255.255.248
    !
    interface FastEthernet0/1.3
    description DMZ
    encapsulation dot1Q 3
    ip address 192.168.3.1 255.255.255.248
    !
    interface FastEthernet0/1.4
    description OFFICE
    encapsulation dot1Q 4
    ip address 192.168.4.1 255.255.255.240
    !
    interface FastEthernet0/1.5
    description ACCOUNTS
    encapsulation dot1Q 5
    ip address 192.168.5.1 255.255.255.248

    Lastly :

    Configure the default route for the Layer 3 switch.
    (config)#ip route 0.0.0.0 0.0.0.0 200.1.1.2

    Note : On layer 2 devices, only 1 vlan can exist with an ip address assigned,
    This ip address is only for managment purpose to device.
    Only 1 vlan will be active status : up up.
    Verify Vlan’s on Layer2 Switch are created “show vlans“, in order to have vlan
    info pass over the trunk to a layer 3 device.