Connectionless Network Service (CLNS) is a Layer 3 protocol similar to IP version 4 (IPv4) for linking hosts (end systems) with routers (intermediate systems) in an Open Systems Interconnection (OSI) network. CLNS and its related OSI protocols, Intermediate System-to-Intermediate System (IS-IS) and End System-to-Intermediate System (ES-IS), are International Organization for Standardization (ISO) standards.
You can configure devices running Junos OS as provider edge (PE) routers within a CLNS network. CLNS networks can be connected over an IP MPLS network core using Border Gateway Protocol (BGP) and MPLS Layer 3 virtual private networks (VPNs). See RFC 2547, BGP/MPLS VPNs.
CLNS uses network service access points (NSAPs), similar to IP addresses found in IPv4, to identify end systems (hosts) and intermediate systems (routers). ES-IS enables the hosts and routers to discover each other. IS-IS is the interior gateway protocol (IGP) that carries ISO CLNS routes through a network.
For more information about CLNS, see the ISO 8473 standards.