Logical Systems Overview

For many years, engineers have combined power supplies, routing hardware and software, forwarding hardware and software, and physical interfaces into a networking device known as a router. Networking vendors have created large routers and small routers, but all routers have been placed into service as individual devices. As a result, the router has been considered a single physical device for most of its history.

The concept of logical systems breaks with this tradition. With Junos OS, you can partition a single router into multiple logical devices that perform independent routing tasks. Because logical systems perform a subset of the tasks once handled by the main router, logical systems offer an effective way to maximize the use of a single routing or switching platform.

Note: Beginning with Junos OS Release 9.3, the logical router feature has been renamed logical system. All configuration statements, operational commands, show command outputs, error messages, log messages, and SNMP MIB objects that contain the string logical-router or logical-routers have been changed to logical-system and logical-systems, respectively.

Traditionally, service provider network design requires multiple layers of switches and routers. These devices transport packet traffic between customers. As seen on the left side of Figure 1, access devices are connected to edge devices, which are in turn connected to core devices.

However, this complexity can lead to challenges in maintenance, configuration, and operation. To reduce such complexity, Juniper Networks support logical systems. Logical systems perform a subset of the actions of the main router and have their own unique routing tables, interfaces, policies, and routing instances. As shown on the right side of Figure 1, a set of logical systems within a single router can handle the functions previously performed by several small routers.

The following protocols and functions are supported on logical systems:

• Open Shortest Path First (OSPF), Intermediate System-to-Intermediate System (IS-IS), Routing Information Protocol (RIP), RIP next generation (RIPng), Border Gateway Protocol (BGP), Resource Reservation Protocol (RSVP), Label Distribution Protocol (LDP), static routes, and Internet Protocol version 4 (IPv4) and version 6 (IPv6) are supported at the [edit logical-systems logical-system-name protocols] hierarchy level.
• Multiprotocol Label Switching (MPLS) provider edge (PE) and core provider router functions, such as Layer 2 virtual private networks (VPNs), Layer 3 VPNs, circuit cross-connect (CCC), Layer 2 circuits, and virtual private LAN service (VPLS) are supported at the [edit logical-systems logical-system-name routing-instances] hierarchy level.
• Multicast protocols, such as Protocol Independent Multicast (PIM) and Distance Vector Multicast Routing Protocol (DVMRP), are supported at the [edit logical-systems logical-system-name protocols] hierarchy level. Rendezvous point (RP) and source designated router (DR) functionality for multicast protocols within a logical system are also supported.
• All policy-related statements available at the [edit policy-options] hierarchy level are supported at the [edit logical-systems policy-options] hierarchy level.
• Most routing options statements available at the [edit routing-options] hierarchy level are supported at the [edit logical-systems routing-options] hierarchy level.
• Graceful Routing Engine switchover (GRES) is supported on Juniper Networks M Series Multiservice Edge Routers, Juniper Networks MX Series Ethernet Services Routers, and Juniper Networks T Series Core Routers. For more information about GRES, see the Junos High Availability Configuration Guide.
• You can assign most interface types to a logical system, including SONET/SDH interfaces, Ethernet interfaces, Asynchronous Transfer Mode (ATM) interfaces, ATM2 intelligent queuing (IQ) interfaces, channelized IQ and Gigabit Ethernet IQ interfaces, aggregated interfaces, Link Services interfaces, and Multilink Services interfaces.
• Source class usage, destination class usage, unicast reverse-path forwarding, class of service, firewall filters, class-based forwarding, and policy-based accounting work with logical systems when you configure these features on the main router.
• Simple Network Management Protocol (SNMP) has been extended to support logical systems and routing instances. A network management system receives instance-aware information in the following format:
  logical-system-name/routing-instance@community

  As a result, a network manager can gather statistics for a specific community within a routing instance within a logical system. For more information on SNMP for logical systems, see the Junos Network Management Configuration Guide.

• SNMP support for logical systems and routing instances has been enhanced. The SNMP manager for a routing instance can now request and manage SNMP data only for that routing instance and other routing instances in the same logical system. As in previous releases, by default the SNMP manager for the default routing instance in the main router (inet.0) can access SNMP data from all routing instances. To restrict that manager's access to the default routing instance only, include the routing-instance-access statement at the [edit snmp] hierarchy level. For more information, see the Junos Network Management Configuration Guide.

The following restrictions apply to logical systems:

• You can configure a maximum of 15 logical systems plus the master logical system on a router. When a configuration session is in use, users who are tied to the same logical system cannot commit configuration changes.
• The router has only one running configuration database, which contains configuration information for the main router and all associated logical systems. When configuring a logical system, users have their own candidate configuration database, which does not become part of the running configuration database until the user issues the commit statement.
• If a logical system experiences an interruption of its routing protocol process (rpd), the core dump output is placed in a file in the following location: /var/tmp/rpd_logical-system-name.core-tarball.number.tgz. Likewise, if you issue the restart routing command in a logical system, only the routing protocol process (rpd) for the logical system is restarted.
• If you configure trace options for a logical system, the output log file is stored in the following location: /var/log/logical-system-name. To monitor a log file within a logical system, issue the monitor start logical-system-name/filename command.
• The following Physical Interface Cards (PICs) are not supported with logical systems: Adaptive Services, Multiservices, ES, Monitoring Services, and Monitoring Services II.
• The Multiservices Dense Port Concentrator (MS-DPC) is not supported with logical systems.
• Generalized MPLS (GMPLS), IP Security (IPsec), point-to-multipoint label-switched paths (LSPs), port mirroring, and sampling are not supported.
• LSP ping and traceroute for autonomous system (AS) number lookup are not supported.
• Class of service (CoS) on logical tunnel (lt) or virtual loopback tunnel (vt) interfaces in a logical system is not supported.
• You cannot include the vrf-table-label statement on multiple logical systems if the core-facing interfaces are channelized or configured with multiple logical interfaces (Frame Relay DLCIs or Ethernet VLANs).
• The master administrator must configure global interface properties and physical interface properties at the [edit interfaces] hierarchy level. Logical system administrators can only configure and verify configurations for the logical systems to which they are assigned. For more information on configuring interfaces, see the Junos Network Interfaces Configuration Guide.

Note: A virtual router does not have the same capabilities as a logical system. A virtual router is a type of simplified routing instance that has a single routing table. A logical system is a partition of the main router and can contain multiple routing instances and routing tables. For example, a logical system can contain multiple virtual router routing instances. As a result, these two entities are not equivalent.