This document outlines some interoperability issues observed with the use of ARP over GMPLS controlled Ethernet router-to- router (PSC) interfaces transiting from a non-Ethernet core, e.g., FSC or LSC core. The document also recommends some procedures to address these issues. The aim of this document is to facilitate and ensure better interworking of GMPLS- capable Label Switching Routers (LSRs), based on experience gained in interoperability testing.