Flow Aware Transport Pseudowire (Fat Pw); Any Transport Over Mpls - Cisco CRS Configuration Manual

Flow Aware Transport Pseudowire (FAT PW)

Flow Aware Transport Pseudowire (FAT PW)
Flow Aware Transport Pseudowires (FAT PW) are used to load-balance traffic in the core when equal cost
multipaths (ECMP) are used. The flow, in this context, refers to a sequence of packets that have the same
source and destination pair. The packets are transported from a source provider edge (PE) to a destination PE.
The following figure shows a FAT PW with two flows distributing over ECMPs and bundle links.
Figure 9: FAT PW with two flows distributing over ECMPs and Bundle-Links
The MPLS labels add an additional label to the stack, called the flow label, which contains the flow information
of a virtual circuit (VC). A flow label is a unique identifier that distinguishes a flow within the PW, and is
derived from the IP payload of a packet. The flow label contains the end of label stack (EOS) bit set and
inserted after the VC label and before the control word (if any). The ingress PE calculates and forwards the
flow label. The FAT PW configuration enables the flow label. The egress PE discards the flow label such that
no decisions are taken based on that label.
All core routers perform load balancing based on the flow-label in the FAT PW. Therefore, it is possible to
distribute flows over ECMPs and link bundles.

Any Transport over MPLS

Any Transport over MPLS (AToM) transports Layer 2 packets over a Multiprotocol Label Switching (MPLS)
backbone. This enables service providers to connect customer sites with existing Layer 2 networks by using
a single, integrated, packet-based network infrastructure. Using this feature, service providers can deliver
Layer 2 connections over an MPLS backbone, instead of using separate networks.
AToM encapsulates Layer 2 frames at the ingress PE router, and sends them to a corresponding PE router at
the other end of a pseudowire, which is a connection between the two PE routers. The egress PE removes the
encapsulation and sends out the Layer 2 frame.
Cisco IOS XR Virtual Private Network Configuration Guide for the Cisco CRS Router, Release 6.1.x
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Implementing Point to Point Layer 2 services