The MPLS protocol, traditionally focused on packet forwarding using labels, has evolved to include advanced mechanisms such as Service Function Chaining (SFC), Alternate-Marking Method (AMM), and in-situ OAM (IOAM). However, many of those mechanisms require extensions to existing specifications in MPLS making them difficult to deploy. To bridge this gap, the IETF MPLS WG proposed the MPLS Network Actions (MNA) framework which provides a unified encoding for signaling network actions and their data within the MPLS stack. Network actions in the MNA framework serve a similar role for MPLS as extension headers (EH) do for IPv6. The network actions can be encoded within the label stack (in-stack) or following the stack (post-stack). In this work, we give a comprehensive overview of the design principles of network actions in the MNA framework and the mechanisms that benefit from this framework. We summarize and explain use cases in the MNA framework. Building on this, we implement the MNA framework in P4 on the Intel Tofino 2 switching ASIC. Our work explores an in-stack data (ISD) implementation of the MNA framework. The implementation can process 51 label stack entries containing 32 network actions at a line rate of 400 Gb/s per port. Additionally, we implement and evaluate an exemplary network action for performance measurement with AMM. Finally, we identify challenges with an MNA in-stack implementation and propose an extension to the signaling procedure.

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