MPLS was originally designed to be simple and fast. As you (and another) have commented, that was to help hardware. But it's grown into something that can be mo

MPLS was originally designed to be simple and fast. As you (and another) have commented, that was to help hardware. But it's grown into something that can be more complicated and even the P switches may read further down the stack to find hash labels etc (but yes, still only lookup using the top label). One benefit was to avoid using CAM but that's getting harder to realise. We don't have just switching labels and these other types may not be consumed, leaving the egress PE popping multiple labels. This is fine and the datapath is designed to make these sorts of packet manipulations, it's just harder to do that at full speed as people get further from the nice, simple original MPLS cases. When using multiple layers of encapsulation, customers don't make the same performance assumptions. Things are worse with SRv6 where the need to read much further into packets is approaching the pain point. Most (all?) network processors have a limit of what you can manipulate at full speed. There's another painful case but I don't think I can discuss that.