IS-IS Protocol has two types of nodes (since the roots of IS-IS are based on ISO Connectionless Network Protocol) i.e. IS & ES. ES (End System): A workstation or network host (limited routing capability) IS (Intermediate Systems): Network devices such as routers with full packet-forwarding capabilities. The word intermediate refers to the capabilities of routers as intermediate forwarding or relay devices. These are also referred to as gateway in some older networking literature of ISO   *If these terms are new to you, I would recommend to review the IS-IS terminology & basics at ATech before proceeding further at: A brief flashback of IS-IS – Part I … Continue reading Adjacencies in IS-IS