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Feb 02

Trunking/VLAN tagging (802.1Q)

IEEE 802.1Q is the networking standard that supports virtual LANs (VLANs) on an Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by bridges and switches in handling such frames.

802.1Q frame tagging

Screen Shot 02-02-17 at 04.25 PM 001

Configuration:

Switch#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Swith(config)#int fastEthernet 0/1
Switch(config-if)#switchport mode trunk
Switch(config-if)#switchport trunk encapsulation dot1q


DTP

The Dynamic Trunking Protocol (DTP) is a proprietary networking protocol developed by Cisco Systems for the purpose of negotiating trunking on a link between two VLAN-aware switches, and for negotiating the type of trunking encapsulation to be used.

 

Administrative Mode Combinations and their Operational Modes

Screen Shot 02-02-17 at 04.55 PM
DTP is not recommended by Cisco. To disable auto-negotiation which is enabled by default run command:

Switch#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)#int fastEthernet 0/1
Switch(config-if)#switchport nonegotiate

Troubleshooting commands:

Switch#show interface fastEthernet 0/1 switchport
!
Switch#show interface trunk

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