"Introduction This memo defines a metric for one-way packet loss across Internet paths. It builds on notions introduced and discussed in the IPPM Framework document@ RFC 2330 [1]; the reader is assumed to be familiar with that document. This memo is intended to be parallel in structure to a companion document for One-way Delay (""A One-way Delay Metric for IPPM"") [2]; the reader is assumed to be familiar with that document. The key words ""MUST""@ ""MUST NOT""@ ""REQUIRED""@ ""SHALL""@ ""SHALL NOT""@ ""SHOULD""@ ""SHOULD NOT""@ ""RECOMMENDED""@ ""MAY""@ and ""OPTIONAL"" in this document are to be interpreted as described in RFC 2119 [5]. Although RFC 2119 was written with protocols in mind@ the key words are used in this document for similar reasons. They are used to ensure the results of measurements from two different implementations are comparable@ and to note instances when an implementation could perturb the network."