The following lists encapsulation service options on Ethernet ports:
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Null
Supports a single service on the port. For example, where a single customer with a single service customer edge (CE) device is attached to the port. The encapsulation ID is always 0 (zero).
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Dot1q
Supports multiple services for one customer or services for multiple customers (Figure: Multiple SAPs on a single port or channel). For example, the port is connected to a multi-tenant unit (MTU) device with multiple downstream customers. The encapsulation ID used to distinguish an individual service is the VLAN ID in the IEEE 802.1Q header.
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Q-in-Q
The q-in-q encapsulation type adds an IEEE 802.1Q tag to the 802.1Q tagged packets entering the network to expand the VLAN space by tagging tagged packets, producing a double tagged frame.
Note: The SAP can be defined with a wildcard for the inner label. (for example, ‟100:*”). In this situation all packets with an outer label of 100 are treated as belonging to the SAP. If, on the same physical link there is also a SAP defined with a q-in-q encap of 100:1, then traffic with the 100:1 encapsulation goes to that SAP and all other traffic with 100 as the first label goes to the SAP with the 100:* definition.
In the dot1q and q-in-q options, traffic encapsulated with tags for which there is no definition are discarded.
