Pseudowire Head-End Termination (PWHT) og PIC-funktioner

PWHT utilizes the Junos operating system and vTrio chip microcode to provide advanced routing, quality of service (HQoS), switching, and security features. The router control plane runs on x86 processors while forwarding is powered by vTrio.

Junos OS Release 17.3 provides enhanced aggregated infrastructure for redundant logical tunnel (RLT) interfaces, with anchor and transport logical interfaces being stacked atop an underlaying control logical interface for easier management.

Pseudowire Head-End Termination (PWHT)

Pseudowire Head-End Termination (PWHT) is an MPLS packet-switched network service that simulates the essential attributes of wire. PWHT connects a Layer 2 circuit from an access node into an L3 service such as L3VPN or EVPN at the provider edge (PE) router – unlike traditional pseudowires which require handoff between PE and metro edge routers; instead it supports L2 dedicated circuits at access nodes leading directly into an L3 virtual private network at PSN edges.

PWHT anchors the pseudowire service logical interface on either a chassis pseudowire logical tunnel (PTL), redundant PTL or RLT. You can configure any of these tunnels or RLTs to support traffic shaping and policing via distribution lists – this feature requires your chassis support the BBE access model.

If you choose PWHT, it is necessary to create two redundant PTL or RLTs and assign multiple logical tunnel interfaces from PWHT’s distribution list as load balancers for load balancing purposes. Each of the interfaces you choose must fall between device counts 0-1; and should serve as anchor points for pseudowire service logical interfaces.

To activate an RLT, at least two logical tunnel interfaces must be linked to it with active links on each. When the number of active links on an RLT decreases to zero, its interface also goes offline along with any stacked pseudowire or PWHT interfaces it connects.

Pseudowire Service Interface (PSI)

The Pseudowire Service Interface (PSI) defines how traffic travels along a pseudowire and serves to emulate MPLS data-plane functionality across an existing transport network. The PSI consists of two parts, the tunnel end and AC part; in turn, tunnel end hosts pseudowire’s media access control address while AC part hosts client’s media access control address (MAC address).

The pseudowire header format includes an 8 bit channel identifier field that supports up to 256 channels in a session, allowing multiplexing of traffic on one pseudowire and optimizing bandwidth utilization in downstream. Unfortunately, however, support for various combinations of channel types is not provided.

PSI not only provides redundancy in head-end termination of Pseudowires, but it also offers multi-home resilience for service edge routers within an EVPN-VPWS framework; this is accomplished using redundant active/standby service edges connected to remote CEs that are reachable via metro aggregation networks – these service Edge Routers then multi-homed using the EVPN-VPWS control plane as they would local CEs.

Each PE router understands which VLANs correspond with specific service edges based on the ESI values configured on each logical tunnel interface. When an egress PE router receives packets from Pseudowire tunnels, its VC label is identified, removed and forwarded directly to its service edge that corresponds with its top label in the stack.

Pseudowire Interface Configuration (PIC)

Pseudowire Interface Configuration (PIC) is a feature used to manage traffic across all active pseudowire interface devices of an anchor redundant logical tunnel. PIC allows you to prevent failure on one link from impacting all subscribers and maximize utilization of any reserved bandwidth that forms part of a PWHT connection. To take advantage of PIC, at least two logical tunnel interfaces (lt) must be configured within your PWHT connection in order for PIC to function.

The pwht config command enables you to specify a maximum number of pseudowire subscriber logical interfaces your router can support, with options like VLAN tagging and gratuitous ARP support available per pseudowire interface. In order to enable VLAN tagging for a tunnel logical tunnel, set an option using a VLAN-based hash key at [edit forwarding-options hash-key family mpls].

Set the maximum number of times that a logical tunnel may fail before being reset and activated as backup tunnel. By default, 100000 failures is permitted before activation is triggered using force switchover command in EXEC mode. You can manually trigger switchover using force switchover command.

Use the xconnect pseudowire autodiscovery command in privileged EXEC mode to automatically discover two endpoint PEs associated with a multiservice pseudowire (MS-PW), formed by stitching together two adjacent single service pseudowires into an MS-PW.

Active-Active Mode Without Targeting

Active-active mode enables multiple devices to process traffic simultaneously, making this configuration popular with streaming services. If any one device fails, another node takes over as active and continues processing requests – providing high availability for critical applications.

Active-active mode without targeting is configured so that all member logical tunnel interfaces (lt) of an anchor redundant logical tunnel (RLT) are set into active status by default, providing increased redundancy as well as automatic load balancing that maximizes use of bandwidth for PWHT connections. A minimum of two RLT member interfaces must be configured before configuring active-active mode without targeting; please see MPLS Pseudowires Configuration for directions on doing so.

This configuration resembles an active-standby setup, except the two BIG-IP devices synchronize their network components and perform failover at the protocol layer, enabling them to process requests simultaneously without becoming single points of failure. This results in increased throughput without single points of failure. TMOS supports this type of active-active clustering with its Device Service Clustering feature. To use it, at least two BIG-IP devices must be in a device group and all must have access to each other simultaneously. Devices should be assigned the same base network components and configured with a central configuration file for maximum synchronization. A nonstop active routing (NSR) implementation using both routers to route packets with identical virtual private wire service identifiers must also be implemented by this group of devices.