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    Routing Engine Software Components

    The Junos OS runs on all Routing Engines in the routing matrix. The software consists of processes that support Internet routing protocols, control the routing matrix's interfaces and chassis, and provide an interface for system management. The processes run on top of a kernel that coordinates the communication among processes and has a direct link to the Packet Forwarding Engine software.

    Routing Engine Software

    The Routing Engine in the TX Matrix Plus router maintains the routing tables used by the routing matrix and controls the routing protocols that run on the routing matrix. The TX Matrix Plus router provides all routing tables, along with updates, to each T1600 router in the routing matrix.

    Each Routing Engine consists of a CPU running Junos OS.

    Caution: We recommend that you run the same Junos OS Release on the master and backup Routing Engines. If you choose to run different Junos OS Releases on the Routing Engines, a change in Routing Engine mastership can cause one or all T1600 routers to be logically disconnected from the TX Matrix Plus router.

    Routing Protocol Process

    The Junos OS routing protocol process controls the routing protocols that run on the TX Matrix Plus router. The routing protocol process starts all configured routing protocols and handles all routing messages. It consolidates the routing information learned from all routing protocols into common routing tables. From this routing information, the routing protocol process determines the active routes to network destinations and installs these routes into the TX Matrix Plus Routing Engine's forwarding table. Finally, the routing protocol process implements the routing policies you specify, which determine how routing information is transferred between the routing protocols and the routing table.

    For complete information about routing concepts, see the Junos OS configuration guides.

    IPv4 Routing Protocols

    The Junos OS implements full IP routing functionality, providing support for IP version 4 (IPv4). The routing protocols are fully interoperable with existing IP routing protocols and provide the scale and control necessary for the Internet core. The software provides support for the following routing and traffic engineering protocols:

    • Unicast routing protocols
      • BGP—Border Gateway Protocol, version 4.
      • ICMP—Internet Control Message Protocol.
      • IS-IS—Intermediate System–to–Intermediate System.
      • OSPF—Open Shortest Path First, version 2.
      • RIP—Routing Information Protocol, version 2.
    • Multicast routing protocols
      • DVMRP—Distance Vector Multicast Routing Protocol.
      • IGMP—Internet Group Management Protocol, versions 1 and 2.
      • MSDP—Multicast Source Discovery Protocol.
      • PIM sparse mode and dense mode—Protocol Independent Multicast.
      • SAP/SDP—Session Announcement Protocol and Session Description Protocol.
    • MPLS application protocols
      • LDP—Label Distribution Protocol.
      • MPLS—Multiprotocol Label Switching.
      • RSVP—Resource Reservation Protocol, version 1.

    IPv6 Routing Protocols

    The Junos OS implements full IP routing functionality, providing support for IP version 6 (IPv6). The routing protocols are fully interoperable with existing IP routing protocols and provide the scale and control necessary for the Internet core. The software provides support for the following unicast routing protocols:

    • BGP—Border Gateway Protocol, version 4.
    • ICMP—Internet Control Message Protocol.
    • IS-IS—Intermediate System–to–Intermediate System.
    • OSPF—Open Shortest Path First, version 3 (OSPFv3).
    • RIP—Routing Information Protocol, version 2.

    Routing and Forwarding Tables

    The primary function of the Junos routing protocol process is maintaining routing tables and using the information in them to determine active routes to network destinations. The process copies information about the active routes into the TX Matrix Plus Routing Engine's forwarding table, which is synchronized with each T1600 router by the kernel synchronization process that runs on each T1600 router's Routing Engine (see Figure 1). The Junos kernel running on each T1600 router's Routing Engine copies its forwarding table to all Packet Forwarding Engines in the router. The Junos kernel running on each T1600 Routing Engine copies its forwarding table to all Packet Forwarding Engines in the router.

    Figure 1: Control Packet Handling for Routing and Forwarding Table Updates

    Control Packet Handling for
Routing and Forwarding Table Updates

    By default, the routing protocol process maintains the following routing tables and uses the information in each table to determine active routes to network destinations:

    • Unicast routing table—Stores routing information for all unicast protocols running on the router, including BGP, IS-IS, OSPF, and RIP. You can also configure additional routes, such as static routes, for inclusion in the routing table. The unicast routing protocols use the routes in this table when advertising routing information to their neighbors.

      In the unicast routing table, the routing protocol process designates routes with the lowest preference values as active. By default, a route's preference value is simply a function of how the routing protocol process learned about the route. You can modify the default preference value by setting routing policies and configuring other software parameters. See Routing Policy.

    • Multicast routing table (cache)—Stores routing information for all multicast protocols running on the router, including DVMRP and PIM. You can configure additional routes for inclusion in the routing table.

      In the multicast routing table, the routing protocol process uses traffic flow and other parameters specified by the multicast routing protocol algorithms to select active routes.

    • MPLS routing table—Stores MPLS label information.

    For unicast routes, the routing protocol process determines active routes by choosing the most preferred route, which is the route with the lowest preference value. By default, the route’s preference value is simply a function of how the routing protocol process learned about the route. You can modify the default preference value using routing policy and with software configuration parameters.

    For multicast traffic, the routing protocol process determines active routes based on traffic flow and other parameters specified by the multicast routing protocol algorithms. The routing protocol process then installs one or more active routes to each network destination into the TX Matrix Plus Routing Engine’s forwarding table.

    You can configure additional routing tables to meet your requirements, as described in the Junos OS Routing Protocols Configuration Guide PDF Document.

    Routing Policy

    By default, all routing protocols place their routes into the routing table. When advertising routes, the routing protocols, by default, advertise only a limited set of routes from the routing table. Specifically, each routing protocol exports only the active routes that were learned by that protocol. In addition, IGPs (IS-IS, OSPF, and RIP) export the direct (interface) routes for the interfaces on which the protocol is explicitly configured.

    For each routing table, you can affect the routes that a protocol places into the table and the routes from the table that the protocol advertises by defining one or more routing policies and then applying them to the specific routing protocol.

    Routing policies applied when the routing protocol places routes into the routing table are called import policies because the routes are being imported into the routing table. Policies applied when the routing protocol is advertising routes that are in the routing table are called export policies because the routes are being exported from the routing table. In other words, the terms import and export are used with respect to the routing table.

    Routing policy enables you to control (filter) which routes are imported into the routing table and which routes are exported from the routing table. Routing policy also allows you to set the information associated with a route as it is being imported into or exported from the routing table. Routing policies applied to imported routes control the routes used to determine active routes, whereas policies applied to exported routes control which routes a protocol advertises to its neighbors.

    You implement routing policy by defining policies. A policy specifies the conditions to use to match a route and the action to perform on the route when a match occurs. For example, when a routing table imports routing information from a routing protocol, a routing policy might modify the route's preference, mark the route with a color to identify it for later manipulation, or prevent the route from even being installed in a routing table. When a routing table exports routes to a routing protocol, a policy might assign metric values, modify the BGP community information, tag the route with additional information, or prevent the route from being exported altogether. You also can define policies for redistributing the routes learned from one protocol into another protocol.

    VPNs

    The Junos OS supports several types of VPNs:

    • Layer 2 VPNs.
    • Layer 3 VPNs.
    • Interprovider VPNs.
    • Carrier-of-Carrier VPNs.

    Interface Process

    The Junos OS interface process manages the physical interface devices and logical interfaces in the routing matrix. It implements the Junos OS command-line interface (CLI) commands and configuration statements that you use to specify interface properties such as location (FPC location in the routing matrix and PIC location on an FPC), the interface type (such as SONET/SDH or ATM), encapsulation, and interface-specific properties. You can configure both interfaces that are currently active and interfaces that might be installed later.

    The Junos OS interface process communicates with the Packet Forwarding Engine through the Junos kernel, enabling the Junos OS to track the status and condition of routing matrix interfaces.

    Chassis Process

    The Junos OS chassis process, which runs on all Routing Engines in the routing matrix, allows you to configure and control the properties of the routing matrix, including conditions that trigger alarms and clock sources. The chassis process running on the TX Matrix Plus Routing Engine manages the components in the TX Matrix Plus chassis, and the chassis process running on each T1600 router Routing Engine manages the components in that router's chassis. All chassis processes running in the routing matrix collectively coordinate the control of the routing matrix switch fabric.

    SNMP and MIB II Processes

    The Junos OS supports the Simple Network Management Protocol (SNMP), versions 1, 2, and 3, which provides a mechanism for monitoring the state of the routing matrix. This software is controlled by the Junos SNMP and Management Information Base (MIB) II processes, which consist of an SNMP master agent and a MIB II agent, and run on the TX Matrix Plus Routing Engine.

    Management Process

    The management process starts all the other Junos OS processes and the CLI when the router boots. It monitors the running Junos processes and makes all reasonable attempts to restart any process that terminates.

    Kernel Synchronization Process

    The kernel synchronization process runs on each T1600 router's Routing Engine (see Figure 1). This process synchronizes the TX Matrix Plus Routing Engine's forwarding table with the forwarding table on a T1600 router. The Junos kernel running on each T1600 router's Routing Engine copies its forwarding table to all Packet Forwarding Engines in the router.

    Routing Engine Kernel

    The Routing Engine kernel provides the underlying infrastructure for all Junos OS processes. The Routing Engines in the T1600 routers run their own kernel, which is synchronized with the kernel running on the TX Matrix Plus Routing Engine (see Kernel Synchronization Process).

    The kernel running on the TX Matrix Plus Routing Engine maintains the master forwarding table for the routing matrix. The kernel running on each T1600 router's Routing Engine copies its local forwarding table—which is synchronized with the master forwarding table by the kernel synchronization process—to all Packet Forwarding Engines in the router.

    Published: 2011-12-19