1-1 What’s Trunk port?
A trunk port is a port that is assigned to carry traffic for all the VLANs.Trunk send Untagged and Tagged information. There are two standards for Trunking:
-
ISL(Cisco)
-
802.1Q(Industry Standard) is 4 Byte which is considered without Native Vlan
Example:
Trunk between two switches
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sw1(config)# int fa0/1
sw1(config-if)# switchport mode trunk
sw2(config)# int fa0/1
sw2(config-vlan)# switchport mode trunk
In older version of Cisco devices first you have to write:
switchport encapsulation dot1q
then
switchport mode trunk
1-2 Changing Native Vlan
For changing Native Vlan just write:
sw1(config)# int fa0/1
sw1(config-if)# switchport trunk native vlan 20
1-3 Allow Specific Vlan
To allow specific vlan just write:
sw1(config)# int fa0/1
sw1(config-if)# switchport allowed vlan 10,20,30
In above-mentioned code, just vlan 10, 20, 30 allowed through trunk port
You can use switchport command with add/all/except/none
sw1(config-if)# switchport allowed vlan 10,20,30
sw1(config-if)# switchport allowed vlan add/all/except/none 10,20,30
1-4 How to see trunk port
switch# show interface trunk
or
switch# show interface fa0/1 switchport
