A new method for encoding MPLS segment routing TE paths

摘要

Segment Routing (SR) architecture has a great potential to replace the MPLS control plane. It simplifies considerably the operation and management of the MPLS networks. A Segment Routing path does not require signaling because it relays on the source routing paradigm, where the path description is directly encoded into the packet's header as a label stack. This has a direct consequence on the size of the label stack which increases linearly with the length of the path. Unfortunately, such approach runs into the routers physical limitation known as the Maximum Stack Depth (MSD), that bounds the maximum number of labels a router can push onto packets. Consequently, it prevents traffic to flow on some of the network paths, leading to underutilization of network resources. Therefore, the MSD restrains the adoption of Segment Routing as it impacts the service provider ability to perform traffic engineering. Several algorithms have been proposed to mitigate the impact of the MSD. They usually rely on an optimization of the SR paths encoding. However, none of them eliminates the impact of the MSD limitation. In this work, we propose a path segmentation approach to definitively eliminate the impact of the MSD. Accordingly, all the possible paths in the network may be considered to forward traffic. This approach is based on the introduction of a new type of Segment Identifiers (SID)s called Targeted SID (TSIDs). We detail the architectural requirements and propose an optimization algorithm to reduce the introduced overhead.