Label switching principles
MPLS

We saw (introduction) that a label was added to the IP packet, but we didn't specify how this was done. Depending on the proposal, this label is simply found in the header of the level 2 frame (IP Switching) or in a header added between the level 2 header and the IP header (Tag Switching, MPLS). In the former case, the core routers use Level 2 processing logic, while in the latter, routers and switches have to be slightly modified to learn how to process a new, very simple header. Thus, MPLS is often referred to as a Layer 2.5 protocol,...