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  • Tatiana Plyushchenko thinks this is interesting:

A router that is running MPLS is known as a label-switching router (LSR). LSRs tag each packet passing through the LSP with a label. This label accomplishes several things, the most important of which is distinguishing the MPLS packet from a regular IP packet, thereby entitling the packet to continue crossing each LSR along the LSP without being subjected to Layer 3 scrutiny. The packet's label is changed by the LSR at every hop, hence the name label-switching...

From

Cover of Juniper Networks® Reference Guide: JUNOS™ Routing, Configuration, and Architecture

Note

LSP packet