Tag :: Dot1q Tag

The Flexible Encapsulation (FlexEncap) feature is used in conjunction with pseudowire, L2, and L3 subinterfaces to match on incoming VLAN tags and retain and/or rewrite them on egress. In the case where VLAN tags are swapped or pushed, the class of service (CoS) field of any new VLAN tag is set based on the configured traffic-class to CoS mapping. That is, based on the traffic class the incoming packet traversed through, the CoS of all VLAN tags of the outgoing packet is determined by the result of the traffic-class to CoS map.

EOS supports the ability to match on a single VLAN tag (example: encapsulation dot1q vlan 10) or a VLAN tag pair (example: encapsulation dot1q vlan 10 inner 20) to map matching packets to an interface. In this case, the encapsulation string is considered consumed by the mapped interface before forwarding, which means that the tags are effectively removed from the incoming packet for the purposes of any downstream forwarding.

User-defined TPIDs allows an arbitrary TPID (Tag Protocol Identifier) to be used with a FlexEncap specification. A TPID is used in Ethernet frames to identify the encapsulation protocol, where standard values like 0x8100 (for IEEE 802.1q VLAN tagging) and 0x88a8 (for IEEE 802.1ad Q-in-Q) are commonly used. However, some network equipment may use non-standard or legacy values such as 0x9100. This feature allows FlexEncap subinterfaces to be configured with an arbitrary TPID to allow interfacing with networking equipment that uses values besides 0x8100 and 0x88a8.