Service OAM packets also include an entropy label and ELI if entropy label capability is signaled for the corresponding tunnel and entropy label is enabled for the service. The EL/ELI pair is inserted at the same level in the label stack as it is in user data packets; that is, within the innermost LSP label context closest to the service payload that has advertised entropy label capability. The EL/ELI pair will therefore always reside at a different level in the label stack from special-purpose labels related to the service payload (for example, the router alert label).
OAM packets at the LSP level, such as LSP ping and LSP trace, do not have the EL/ELI pair inserted.