CLNS Overview

Connectionless Network Service (CLNS) is a Layer 3 protocol similar to 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 SRX and J Series devices as provider edge (PE) routers within a CLNS network. CLNS networks can be connected over an IP MPLS network core using BGP and MPLS Layer 3 virtual private networks (VPNs). For more information, see RFC 2547, BGP/MPLS VPNs.

You can use either the J-Web configuration editor or CLI configuration editor to configure CLNS.

For more information about CLNS, IS-IS, and ES-IS, see the Junos Routing Protocols Configuration Guide.

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.

Depending on your network topology, one or more of the following components are needed to route within a CLNS environment:

• ES-IS—Provides the basic interaction between CLNS hosts (end systems) and routers (intermediate systems). Using ES-IS, hosts advertise their ISO NSAP addresses and subnetwork point-of-attachment (SNPA) addresses to other routers and hosts attached to the subnetwork. The resolution of Layer 3 ISO NSAPs to Layer 2 SNPAs by ES-IS is equivalent to ARP within an IPv4 network.

  If a CLNS island does not contain any end systems, you do not need to configure ES-IS on a device.

• IS-IS extensions—Provide the basic IGP support for collecting intradomain routing information for CLNS destinations within a CLNS network. Routers learning host addresses through ES-IS can advertise them to other routers (intermediate systems) using IS-IS.
• Static routes—You can configure static routes to exchange CLNS routes within a CLNS island. You can use static routing with or without IS-IS.
• Border Gateway Protocol (BGP) extensions—BGP extensions allow BGP to carry CLNS VPN network layer reachability information (NLRI) between PE routers. Each CLNS route is encapsulated into a CLNS VPN NLRI and propagated between remote sites in a VPN.

For more information about CLNS, see the ISO 8473 standards. For more information about IS-IS, see the ISO 10589 standard. For more information about ES-IS, see the ISO 9542 standard.