FPE-based PW port operational state

The ability of the stitching service to forward traffic drives the FPE-based PW port operational state. This includes the operational status of the stitching service and, if the external PW is TLDP signaled, the PW status bits. The stitching service operational status transitions to a non-operational state if the EVPN network destination, a BGP-VPWS spoke-SDP, or a configured spoke-SDP is operationally down.

With a TLDP-signaled PW, the operational state of the PW port depends on the PW status bits received from the peer, even if the stitching service is operationally up:

The PW port transitions into a non-operational state if the PW Preferential Forwarding bit (pwFwdingStandby) is received from the peer (the PW is in standby mode).
The PW port transitions into a non-operational state if the Local Attachment Circuit (LAC) or Local Packet Switched Network (PSN) faults are received from the peer (lacIngressFault, lacEgressFault, psnIngressFault, and psnEgressFault). The operator must explicitly enable this behavior through CLI. By default, the aforementioned fault bits received from the peer do not affect the state of the PW port.

The operational flag for a non-operational PW-port is set to stitchingSvcTxDown.

Transitioning of the PW port into the down state because of a PXC failure (for example physical port fails) brings the stitching service down with the following result:

In case of a TLDP-signaled PW, the psnIngressFault and psnEgressFault PW status bits are propagated to the remote end, indicating that the local stitching service is down.
In case of an EVPN, the EVPN route is withdrawn, indicating that the local stitching service is down.
In case of a BGP-VPWS, the BGP-VPWS ‛D’ bit of the Layer 2 Information Extended Community flag field is set, indicating that the local stitching service is down.

By default, if a PW port is mated to a T-LDP-signaled PW (for example, a spoke-SDP) across an FPE in an Epipe service, the PW port operational state only reacts to the following PW status bit being set on the received T-LDP status message:

pwFwdingStandby (5) -- Pseudo Wire in Standby mode

When the down-on-peer-tldp-pw-status-faults command is configured, the PW port only goes locally operationally down if any of the following PW status bits are received on the mate spoke-SDP:

pwNotForwarding (0), -- Pseudo Wire Not Forwarding

lacIngressFault (1), -- Local Attachment Circuit Rx Fault

lacEgresssFault (2), -- Local Attachment Circuit Tx Fault

psnIngressFault (3), -- Local PSN-facing PW Rx Fault

psnEgressFault (4), -- Local PSN-facing PW Tx Fault

If the configuration is removed, the system no longer takes the mate PW status fault bits into account in the operational state of the PW port.

Note: The stitching service in this context is an Epipe service in vc-switching mode for BGP-VPWS or T-LDP signaled PW, as follows:

Classic CLI commands

configure
      service epipe epipe-id customer cust-id vc-switching [create]
            pw-port pw-port-id fpe fpe-id
            spoke-sdp sdp-id:vc-id [create]
                  or 
            bgp-vpws

MD-CLI commands

configure 
      service epipe string 
            customer reference vc-switching 
            spoke-sdp sdp-id:vc-id
                  or
            bgp-vpws
      pw-port number 
            epipe epipe-id 
                fpe-id reference

Note: The stitching service in this context is an Epipe service in a non-VC-switching mode for EVPN, as follows:

Classic CLI commands

configure
      service epipe epipe-id customer cust-id create
            pw-port pw-port-id fpe fpe-id
            bgp-evpn

MD-CLI commands

configure
      service epipe string 
            customer reference
            bgp-evpn
      pw-port number 
            epipe epipe-id 
                fpe-id reference