North Carolina State University North Carolina State University Juniper Networks University of Oslo This document defines a data structure that can be appended to selected ICMP messages. The ICMP extension defined herein can be used to gain visibility on environmental sustainability information on the Internet by providing per-hop (i.e., per topological network node) power metrics and other current or future sustainability metrics. This will contribute to achieving an objective mentioned in the IAB E-Impact workshop. The techniques presented are useful not only in a transactional setting (e.g., a user-issued traceroute or a ping request), but also in a scheduled automated setting where they may be run periodically in a mesh across an administrative domain to map out environmental sustainability metrics.