When an 802.1Q Ethernet frame is encapsulated for transport over a VC tunnel, the entire frame is included, except for the preamble and FCS.
There is a configuration option that determines whether the 4-byte VLAN (Virtual LAN) tag field is included in the transmitted packet. By default, the tag field is not included. If the tag field is not included, the egress LER may add one. If it is included, the tag service identifier may be overwritten by the egress LER. The ability to add a tag field or to overwrite the service identifier at the egress node allows two (possibly independently administered) VLAN segments with different VLAN IDs to be treated as a single VLAN.
The following command can be used to include the VLAN tag field:
configure l2vpn [vpls vpls_name | vpws vpws_name] {dot1q [ethertype hex_number | tag [include | exclude]]} {mtu number}
This command can also be used to control the overwriting of the 802.1Q ethertype when the VLAN tag field is included. In this case, the ingress node prior to transmitting the encapsulated packet overwrites the ethertype. This allows devices with a configurable VLAN tag ethertype to interoperate.
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