End System to Intermediate System Protocol(ES- IS) is an ISO protocol that defines how end systems (ES) make themselves known to intermediate systems (IS) or how routers register with end systems. OSI refers to end systems as nodes or user devices, and intermediate systems as routers.
ES-IS protocols are also referred to as routable protocols. ES-IS protocols include the IP protocol, the IPX protocol, Internetwork Packet Exchange Protocol (IPX), and the XNS protocol, Xerox Network System (XNS), but also the Address Resolution Protocol ( ARP). The ES-IS protocol was specified by the International Organization for Standardization (ISO) as part of the Open Systems Interconnection (OSI) under ISO 8473.
The ES-IS protocol can be used to determine the presence and availability of end devices on specific subnets, as well as to determine the routers that can transport data packets to the end nodes. The ES-IS protocol can be used together with the IS-IS protocol in extensive network configurations.