VPLS Service Pseudowire VLAN Tag Processing

VPLS services can be connected using pseudowires that can be provisioned statically or dynamically and are represented in the system as either a mesh or a spoke-SDP. The mesh and spoke-SDP can be configured to process zero, one, or two VLAN tags as traffic is transmitted and received. In the transmit direction, VLAN tags are added to the frame being sent, and in the received direction, VLAN tags are removed from the frame being received. This is analogous to the SAP operations on a null, dot1q, and QinQ SAP.

The system expects a symmetrical configuration with its peer; specifically, it expects to remove the same number of VLAN tags from received traffic as it adds to transmitted traffic. When removing VLAN tags from a mesh or spoke-SDP, the system attempts to remove the configured number of VLAN tags (see the following configuration information); if fewer tags are found, the system removes the VLAN tags found and forwards the resulting packet. As some of the related configuration parameters are local and not communicated in the signaling plane, an asymmetrical behavior cannot always be detected and so cannot be blocked. With an asymmetrical behavior, protocol extractions do not necessarily function as they would with a symmetrical configuration, resulting in an unexpected operation.

The VLAN tag processing is configured as follows on a mesh or spoke-SDP in a VPLS service:

Zero VLAN tags processed — VPLS Service Pseudowire VLAN Tag Processing. This requires the configuration of vc-type ether under the mesh-SDP or spoke-SDP, or in the related PW template.
One VLAN tag processed — This requires one of the following configurations:
- vc-type vlan under the mesh-SDP or spoke-SDP, or in the related PW template
- vc-type ether and force-vlan-vc-forwarding under the mesh-SDP or spoke-SDP, or in the related PW template
Two VLAN tags processed—This requires the configuration of force-qinq-vc-forwarding [c-tag-c-tag | s-tag-c-tag] under the mesh-SDP or spoke-SDP, or in the related PW template.

The PW template configuration provides support for BGP VPLS services and LDP VPLS services using BGP Auto-Discovery.

The following restrictions apply to VLAN tag processing:

The configuration of vc-type vlan and force-vlan-vc-forwarding is mutually exclusive.
BGP VPLS services operate in a mode equivalent to vc-type ether; consequently, the configuration of vc-type vlan in a PW template for a BGP VPLS service is ignored.
force-qinq-vc-forwarding [c-tag-c-tag | s-tag-c-tag] can be configured with the mesh-SDP or spoke-SDP signaled as either vc-type ether or vc-type vlan.
The following are not supported with force-qinq-vc-forwarding [c-tag-c-tag | s-tag-c-tag] configured under the mesh-SDP or spoke-SDP, or in the related PW template:
- Routed, E-Tree, or PBB VPLS services (including B-VPLS and I-VPLS)
- L2PT termination on QinQ mesh-SDP or spoke-SDPs
- IGMP/MLD/PIM snooping within the VPLS service
- force-vlan-vc-forwarding under the same spoke-SDP or PW template
- Eth-CFM LM tests

Table 1 and Table 2 describe the VLAN tag processing with respect to the zero, one, and two VLAN tag configuration described for the VLAN identifiers, Ethertype, ingress QoS classification (dot1p/DE), and QoS propagation to the egress (which can be used for egress classification and, or to set the QoS information in the innermost egress VLAN tag).

Table 1. VPLS Mesh and Spoke-SDP VLAN Tag Processing: Ingress
Ingress (received on mesh or spoke-SDP)	Zero VLAN tags	One VLAN tag	Two VLAN Tags (enabled by force-qinq-vc-forwarding [c-tag-c-tag \| s-tag-c-tag]
VLAN identifiers	—	Ignored	Both inner and outer ignored
Ethertype (to determine the presence of a VLAN tag)	—	0x8100 or value configured under sdp vlan-vc-etype	Both inner and outer VLAN tags: 0x8100, or outer VLAN tag value configured under sdp vlan-vc-etype (inner VLAN tag value must be 0x8100)
Ingress QoS (dot1p/DE) classification	—	Ignored	Both inner and outer ignored
QoS (dot1p/DE) propagation to egress	Dot1p/DE=0	Dot1p/DE taken from received VLAN tag	Dot1p/DE taken as follows: If the egress encapsulation is a Dot1q SAP, Dot1p/DE bits are taken from the outer received VLAN tag. If the egress encapsulation is QinQ SAP, the s-tag bits are taken from the outer received VLAN tag and the c-tag bits from the inner received VLAN tag.

Table 2. VPLS Mesh and Spoke-SDP VLAN Tag Processing: Egress
Egress (sent on mesh or spoke-SDP)	Zero VLAN tags	One VLAN tag	Two VLAN Tags (enabled by force-qinq-vc-forwarding [c-tag-c-tag \| s-tag-c-tag]
VLAN identifiers (set in VLAN tags)	—	For one VLAN tag, one of the following applies: the vlan-vc-tag value configured in PW template or value under the mesh/spoke-SDP value from the inner tag received on a QinQ SAP or QinQ mesh/spoke-SDP value from the VLAN tag received on a dot1q SAP or mesh/spoke-SDP (with vc-type vlan or force-vlan-vc-forwarding) value from the outer tag received on a qtag.* SAP 0 if there is no service delimiting VLAN tag at the ingress SAP or mesh/spoke-SDP	The inner and outer VLAN tags are derived from one of the following: vlan-vc-tag value configured in PW template or under the mesh/spoke-SDP: If c-tag-c-tag is configured, both inner and outer tags are taken from the vlan-vc-tag value. If s-tag-c-tag is configured, only the s-tag value is taken from vlan-vc-tag. value from the inner tag received on a QinQ SAP or QinQ mesh/spoke-SDP for the c-tag-c-tag option and value from outer/inner tag received on a QinQ SAP or QinQ mesh/spoke-SDP for the s-tag-c-tag configuration option value from the VLAN tag received on a dot1q SAP or mesh/spoke-SDP (with vc-type vlan or force-vlan-vc-forwarding) for the c-tag-c-tag option and value from the VLAN tag for the outer tag and zero for the inner tag
			value from the outer tag received on a qtag.* SAP for the c-tag-c-tag option and value from the VLAN tag for the outer tag and zero for the inner tag value 0 if there is no service delimiting VLAN tag at the ingress SAP or mesh/spoke-SDP Ethertype (set in VLAN tags)
Ethertype (set in VLAN tags)	—	0x8100 or value configured under sdp vlan-vc-etype	Both inner and outer VLAN tags: 0x8100, or outer VLAN tag value configured under sdp vlan-vc-etype (inner VLAN tag value is 0x8100)
Egress QoS (dot1p/DE) (set in VLAN tags)	—	Taken from the innermost ingress service delimiting tag, one of the following applies: the inner tag received on a QinQ SAP or QinQ mesh/spoke-SDP value from the VLAN tag received on a dot1q SAP or mesh/spoke-SDP (with vc-type vlan or force-vlan-vc-forwarding) value from the outer tag received on a qtag.* SAP	Inner and outer dot1p/DE: If c-tag-c-tag is configured, the inner and outer dot1p/DE bits are both taken from the innermost ingress service delimiting tag. It can be one of the following: inner tag received on a QinQ SAP value from the VLAN tag received on a dot1q SAP or spoke-SDP (with vc-type vlan or force-vlan-vcforwarding) value from the outer tag received on a qtag.* SAP
Egress QoS (dot1p/DE) (set in VLAN tags)	—	0 if there is no service delimiting VLAN tag at the ingress SAP or mesh/spoke-SDP Note that neither the inner nor outer dot1p/DE values can be explicitly set.	0 if there is no service delimiting VLAN tag at the ingress SAP or mesh/spoke-SDP If s-tag-c-tag is configured, the inner and outer dot1p/DE bits are taken from the inner and outer ingress service delimiting tag (respectively). They can be: inner and outer tags received on a QinQ SAP or QinQ mesh/spoke-SDP value from the VLAN tag received on a dot1q SAP or mesh/spoke-SDP (with vc-type vlan or force-vlan-vc-forwarding) for the outer tag and zero for the inner tag value from the outer tag received on a qtag.* SAP for the outer tag and zero for the inner tag value 0 if there is no service delimiting VLAN tag at the ingress SAP or mesh/spoke-SDP

Any non-service delimiting VLAN tags are forwarded transparently through the VPLS service. SAP egress classification is possible on the outermost customer VLAN tag received on a mesh or spoke-SDP using the ethernet-ctag parameter in the associated SAP egress QoS policy.