This document compares SRv4 and SRv6, which are segment routing technologies built on MPLS and IPv6 respectively. It first provides background on MPLS and how it routes traffic based on labels instead of addresses. It then introduces segment routing, which adds a segment label stack to packets to control the transmission path. The rest of the document outlines how segment routing works by encapsulating packets at the ingress node with a path of segments, having each segment endpoint forward the packet to the next until it reaches the egress node and final destination.