Epipe service pseudowire VLAN tag processing

Distributed Epipe services are connected using a pseudowire, which can be provisioned statically or dynamically and is represented in the system as a spoke-SDP. The spoke-SDP can be configured to process zero, one, or two VLAN tags as traffic is transmitted and received; see Table 1 and Table 2 for the ingress and egress tag processing. In the transmit direction, VLAN tags are added to the frame being sent. 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 spoke-SDP, the system attempts to remove the configured number of VLAN tags. If fewer tags are found, the system removes the VLAN tags found and forwards the resulting packet.

Because 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, a protocol extraction does not necessarily function as it would with a symmetrical configuration, resulting in an unexpected operation.

The VLAN tag processing is configured as follows on a spoke-SDP in an Epipe service:

Zero VLAN tags processed — This requires the configuration of vc-type ether under the spoke-SDP, or in the related PW template.
One VLAN tag processed — This requires one of the following configurations:
- vc-type vlan under the spoke-SDP or in the related PW template
- vc-type ether and force-vlan-vc-forwarding under the 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 spoke-SDP or in the related PW template.

The PW template configuration provides support for BGP VPWS services.

The following restrictions apply to VLAN tag processing:

The configuration of vc-type vlan and force-vlan-vc-forwarding is mutually exclusive.
force-qinq-vc-forwarding [c-tag-c-tag | s-tag-c-tag] can be configured with the 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 spoke-SDP, or in the related PW template:
- Multi-segment pseudowires.
- PBB-Epipe services
- force-vlan-vc-forwarding under the same spoke-SDP or PW template
- Eth-CFM LM tests are NOT supported on UP MEPs when force-qinq-vc-forwarding is enabled.

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 or 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. Epipe spoke-SDP VLAN tag processing: ingress
Ingress (received on 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)	N/A	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 The egress cannot be a spoke-sdp because force-qinq-vc-forwarding does not support multi-segment PWs.

Table 2. Epipe-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)	—	The tag is derived from one of the following: the vlan-vc-tag value configured in PW template or under the spoke-SDP value from the inner tag received on a QinQ SAP or QinQ spoke-SDP value from the VLAN tag received on a dot1q SAP or 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 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 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 for the c-tag-c-tag option and value from outer/inner tag received on a QinQ SAP for the s-tag-c-tag configuration option value from the VLAN tag received on a dot1q 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 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 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)	—	The tag taken from the innermost ingress service delimiting tag can be one of the following: The inner tag received on a QinQ SAP or QinQ spoke-SDP value from the VLAN tag received on a dot1q SAP or 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 value from the outer tag received on a qtag.* SAP value 0 if there is no service delimiting VLAN tag at the ingress SAP
		0 if there is no service delimiting VLAN tag at the ingress SAP or spoke-SDP Note that neither the inner nor outer dot1p/DE values can be explicitly set.	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 value from the VLAN tag received on a dot1q SAP 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 Note that neither the inner nor outer dot1p/DE values can be explicitly set.

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