Introduction to IEEE 802.1Q Tunnel

Today I am going to talk about configuration of 802.1Q tunnel. We are going to talk about the IEEE 802.1Q tunnel configuration on cisco routers and by default, in Cisco switches the 802.1Q tunnel is disable and switchport mode is auto by default.Tagging of IEEE 802.1Q native VLAN packets on all IEEE 802.1Q trunk ports is also disabled.

What is IEEE 802.1Q tunneling?
IEEE 802.1Q tunnel permits the use of a one VLAN to support multiple customer VLANs. The customer switches are trunk connected, but with IEEE 802.1Q tunnelling  the service provider switches only use one service provider VLAN to carry all the customer VLANs, in its place of straight transport all the customer VLANs.

Basic diagram showing the IEEE 802.1Q tunnelling between two different customers via single service provider

Fig 1.1- IEEE 802.1q Tunnelling 

Restrictions on IEEE 802.1Q tunneling 
  • Fallback bridging is not maintained on tunnel ports. Since all IEEE 802.1Q-tagged packets received from a tunnel port are treated as non-IP packets, if fallback bridging is enabled on VLANs that have tunnel ports configured, IP packets would be improperly bridged across VLANs. Therefore, you must not enable fallback bridging on VLANs with tunnel ports.
  • EtherChannel port groups are compatible with tunnel ports as long as the IEEE 802.1Q configuration is consistent within an EtherChannel port group.
  • Dynamic Trunking Protocol (DTP) is not compatible with IEEE 802.1Q tunnelling because you must manually configure asymmetric links with tunnel ports and trunk ports.

RouteXP_Switch> enable
RouteXP_Switch # configure terminal
RouteXP_Switch (config)# interface gigabitethernet2/0/1
RouteXP_Switch (config-if) # switchport access vlan 2
RouteXP_Switch (config-if) # switchport mode dot1q-tunnel
RouteXP_Switch (config-if) # exit
RouteXP_Switch (config)# vlan dot1q tag native
RouteXP_Switch (config)# end

Show Commands
RouteXP_Switch # show dot1q-tunnel
RouteXP_Switch # show running-config interface
RouteXP_Switch # show vlan dot1q native

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