Overview

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 34, 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 now supports logical routers. Logical routers 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 34, a set of logical routers within a single router can handle the functions previously performed by several small routers.

The following protocols and functions are supported on logical routers:

• 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-routers logical-router-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-routers logical-router-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-routers logical-router-name protocols] hierarchy level. Rendezvous point (RP) and source designated router (DR) functionality for multicast protocols within a logical router is also supported.
• All policy-related statements available at the [edit policy-options] hierarchy level are supported at the [edit logical-routers policy-options] hierarchy level.
• Most routing options statements available at the [edit routing-options] hierarchy level are supported at the [edit logical-routers routing-options] hierarchy level. Only the route-record statement is not supported at the [edit logical-routers routing-options] hierarchy level.
• Graceful Routing Engine switchover (GRES) is supported on J-series, M-series, MX-series, and T-series routers. For more information about GRES, see the JUNOS High Availability Configuration Guide.
• You can assign most interface types to a logical router, 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 routers when you configure these features on the main router.
• Simple Network Management Protocol (SNMP) has been extended to support logical routers and routing instances. A network management system receives instance-aware information in the following format:

  logical-router-name / routing-instance @ community

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

The following restrictions apply to logical routers:

• You can configure a maximum of 15 logical routers on a router.
• The router has only one configuration file which contains configuration information for the main router and all associated logical routers.
• If a logical router 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-router-name.core-tarball.number.tgz. Likewise, if you issue the restart routing command in a logical router, only the routing protocol process (rpd) for the logical router is restarted.
• If you configure trace options for a logical router, the output log file is stored in the following location: /var/log/logical-router-name . To monitor a log file within a logical router, issue the monitor start logical-router-name/filename command.
• The following Physical Interface Cards (PICs) are not supported with logical routers: Adaptive Services, ES, Monitoring Services, and Monitoring Services II.
• 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 router is not supported.
• You cannot include the vrf-table-label statement on multiple logical routers if the core-facing interfaces are channelized or configured with multiple logical interfaces (Frame Relay DLCIs or Ethernet VLANs).

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