  Validating network paths taken by packets is critical for a secure Internet
architecture. Any feasible solution must both enforce packet forwarding along
endhost-specified paths and verify whether packets have taken those paths.
However, neither enforcement nor verification is supported by the current
Internet. Due likely to a long-standing confusion between routing and
forwarding, only limited solutions for path validation exist in the literature.
This survey article aims to reinvigorate research in to the significant and
essential topic of path validation. It crystallizes not only how path
validation works but also where seemingly qualified solutions fall short. The
analyses explore future research directions in path validation toward improving
security, privacy, and efficiency.
