This chapter provides information about Virtualized Service Router (VSR) pseudowire ports (PW ports), process overview, and implementation notes.
A PW port represents an extraction point of a payload carried within a tunnel. This payload is extracted onto a PW SAP within a service context (such as a Epipe, VPRN or IES). Various types of tunnels can be supported and the details of each tunnel type whose payload is terminated on a PW port is described in the following sections.
The entry point of a tunnel depends on the routing conditions in the network. To make a distinction between a PW port with a fixed connection to a physical port (a virtual port in the VSR), and a PW port that is free to switch between the ports, the latter is referred to as a Flex PW port.
A Flex PW port is bound to a list of ports, and the tunnel associated with the Flex PW port can be routed (and rerouted) through any port in that list. If traffic is re-routed through a different port due to failure in the network, the Flex PW port continues to be the terminating point of the tunnel, with minimal packet loss incurred during the switchover. See Figure 215.
Each port eligible to transmit traffic on a Flex PW port, must be added to a pw-port-list.
Only hybrid ports (configure port port-id ethernet mode hybrid) can be members of a PW port list.
A port used by Flex PW port can be shared with any other Layer 2 or Layer 3 service. For example, a Layer 3 interface using a regular SAP can be associated with a VPRN service, while the underlying port is also used by a Flex PW port. Another regular SAP from the same port can be associated with a VPLS or Epipe service at the same time.
Follow these rules when populating a PW port list:
From this, an operator can consider adding all ports that are in hybrid mode to a PW port list from the beginning of the system configuration. This ensures that those ports can be used by Flex PW port at any later time, independently of their current use.
Traffic loss during port switchover depends on several factors:
The egress queues on the new port must be recreated. However, this does not incur additional downtime because a spare egress queue is always present on a port (referred to as a failover queue) and is used while per PW SAP egress queues are being created.
Depending on the scale and network load, downtime during a switchover can range from the sub-second range to a several seconds.
Egress queues are attached to the port that is used by a Flex PW port to forward traffic (a Flex PW port is bound to one of the ports in the PW port list). In similar fashion, if an egress port scheduler is used, it is attached to the same port. However, the egress port schedulers must be associated by configuration with every port in the PW port list while egress queues are instantiated only on a single port. During a port switchover, egress queues are recreated on the new port and while this is occurring, the failover queue is used to forward traffic. Each port has a single egress failover queue that is used to forward traffic while SAP or subscriber queues are being recreated during transitioning events. A failover queue is an expedited queue with a CIR of 0 and this queue cannot be tied to an egress port scheduler.
On the other hand, egress port scheduler must be configured by the operator in advance on each port in the PW port list so that it can be ready to treat traffic immediately after its children queues are recreated on this port.
Policers are used on ingress and they do not need to be recreated during port switchover. Instead, they are re-mapped to a new port.
A sample QoS configuration is provided below:
The MPLS-based spoke SDP tunnel type is supported on a Flex PW port.
An MPLS-based spoke SDP can be rerouted between the ports defined in the PW port list and still be mapped to the same PW port based on the service label. Ethernet payload within the spoke SDP can be extracted onto a PW SAP with minimal traffic loss during port switchover.
The operational state of the Flex PW port is driven by the ability of the Epipe service (that ties the PW port to the spoke SDP) to forward traffic. The following events renders the PW port non-operational and triggers propagation of the PW status bits toward the remote end:
The corresponding PW status bits that are propagated to the remote end raises the counterpart flags on the remote end.
The corresponding PW status bits that are propagated to the remote end raises the counterpart flags on the remote end.
Statistics for the number of forwarded or dropped packets pr octets per direction on a Flex PW port associated with a MPLS based spoke SDP are maintained per the spoke SDP. Octets field counts octets in customer frame (including customer’s Ethernet header with VLAN tags).
The following command is used to display Flex PW port statistics along with the status of the spoke SDP associated with the PW port:
The termination of a MPLS-based spoke SDP on a Flex PW port follows the common provisioning framework: