MPLS Network Actions: Technological Overview and P4-Based Implementation on a High-Speed Switching ASIC

TL;DR

This paper overviews MPLS Network Actions (MNA), compares it to IPv6 extension headers, and presents a high-speed P4 hardware implementation demonstrating scalability, performance, and practical use cases like link measurement and bandwidth reservation.

Contribution

It provides a comprehensive overview of MNA, compares it with IPv6 EHs, and introduces P4-MNA hardware implementation with scalability and performance evaluation.

Findings

P4-MNA runs at 400 Gb/s per port with negligible delay impact.

MNA supports use cases like link measurement and bandwidth reservation.

Hardware constraints influence the number of supported network actions.

Abstract

In MPLS, packets are encapsulated with labels that add domain-specific forwarding information. Special purpose labels were introduced to trigger special behavior in MPLS nodes but their number is limited. Therefore, the IETF proposed the MPLS Network Actions (MNA) framework. It extends MPLS with new features, some of which have already been defined to support relevant use cases. This paper provides a comprehensive technological overview of MNA concepts and use cases. It compares MNA to IPv6 extension headers (EHs) that serve a similar purpose, and argues that MNA can be better deployed than EHs. It then presents P4-MNA, a first hardware implementation running at 400 Gb/s per port. Scalability and performance of P4-MNA are evaluated, showing negligible impact on processing delay caused by network actions. Moreover, the applicability of MNA is demonstrated by implementing the use cases of link-specific packet loss measurement using the alternate-marking-method (AMM) and bandwidth reservation using network slicing. We identify header stacking constraints resulting from hardware resources and from the number of network actions that must be supported according to the MNA encoding. They make an implementation for hardware that can only parse a few MPLS headers infeasible. We propose to make the number of supported network actions a node parameter and signal this in the network. Then, an upgrade to MNA is also feasible for hardware with fewer available resources. We explain that for MNA with in-stack data (ISD), some header bits must remain unchanged during forwarding, and give an outlook on post-stack data (PSD).