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Virtual Chassis Components Overview

 

A Virtual Chassis configuration for MX Series 3D Universal Edge Routers interconnects two MX Series routers into a logical system that you can manage as a single network element.Figure 1 illustrates a typical topology for a two-member MX Series Virtual Chassis.

Figure 1: Sample Topology for MX Series Virtual Chassis
Sample Topology
for MX Series Virtual Chassis

This overview describes the basic hardware and software components of the Virtual Chassis configuration illustrated in Figure 1, and covers the following topics:

Virtual Chassis Primary Router

One of the two member routers in the Virtual Chassis becomes the primary router, also known as the protocol primary. The Virtual Chassis primary router maintains the global configuration and state information for both member routers, and runs the chassis management processes. The primary Routing Engine that resides in the Virtual Chassis primary router becomes the global primary for the Virtual Chassis.

Specifically, the primary Routing Engine that resides in the Virtual Chassis primary router performs the following functions in a Virtual Chassis:

  • Manages both the primary and backup member routers

  • Runs the chassis management processes and control protocols

  • Receives and processes all incoming and exception path traffic destined for the Virtual Chassis

  • Propagates the Virtual Chassis configuration (including member IDs, roles, and configuration group definitions and applications) to the members of the Virtual Chassis

The first member of the Virtual Chassis becomes the initial primary router by default. After the Virtual Chassis is formed with both member routers, the Virtual Chassis Control Protocol (VCCP) software runs a primary-role election algorithm to elect the primary router for the Virtual Chassis configuration.

Note

You cannot configure primary-role election for an MX Series Virtual Chassis.

Virtual Chassis Backup Router

The member router in the Virtual Chassis that is not designated as the primary router becomes the backup router, also known as the protocol backup. The Virtual Chassis backup router takes over the primary role of the Virtual Chassis if the primary router is unavailable, and synchronizes routing and state information with the primary router. The primary Routing Engine that resides in the Virtual Chassis backup router becomes the global backup for the Virtual Chassis.

Specifically, the primary Routing Engine that resides in the Virtual Chassis backup router performs the following functions in a Virtual Chassis:

  • If the primary router fails or is unavailable, takes over the primary role of the Virtual Chassis in order to preserve routing information and maintain network connectivity without disruption

  • Synchronizes routing and application state, including routing tables and subscriber state information, with the primary Routing Engine that resides in the Virtual Chassis primary router

  • Relays chassis control information, such as line card presence and alarms, to the primary router

Virtual Chassis Line-Card Role

Note

The line-card role is not supported in the preprovisioned configuration for a two-member MX Series Virtual Chassis. The line-card role applies only in the context of split detection behavior.

A member router functioning in the line-card role runs only a minimal set of chassis management processes required to relay chassis control information, such as line card presence and alarms, to the Virtual Chassis primary router.

You cannot explicitly configure a member router with the line-card role. However, if the backup router fails in a two-member Virtual Chassis configuration and split detection is enabled (the default behavior), the primary router takes a line-card role, and line cards (FPCs) that do not host Virtual Chassis ports go offline. This state effectively isolates the primary router and removes it from the Virtual Chassis until connectivity is restored. As a result, routing is halted and the Virtual Chassis configuration is disabled.

Virtual Chassis Ports

Virtual Chassis ports are special Ethernet interfaces that form a point-to-point connection between the member routers in a Virtual Chassis. When you create a Virtual Chassis, you must configure the Virtual Chassis ports on Modular Port Concentrator/Modular Interface Card (MPC/MIC) interfaces. After you configure a Virtual Chassis port, it is renamed vcp-slot/pic/port (for example, vcp-2/2/0), and the line card associated with that port comes online. For example, the sample Virtual Chassis topology shown in Figure 1 has a total of four Virtual Chassis ports (represented by the dots), two on each of the two member routers.

After a Virtual Chassis port is configured, it is dedicated to the task of interconnecting member routers, and is no longer available for configuration as a standard network port. To restore this port to the global configuration and make it available to function as a standard network port, you must delete the Virtual Chassis port from the Virtual Chassis configuration.

Note

The Junos® operating system (Junos OS) software enables you to preconfigure ports that are currently unavailable for use. Although a Virtual Chassis port is unavailable for use as a standard network port, you can configure this port as a standard network port even after you configure it as a Virtual Chassis port. However, the router does not apply the configuration until you delete the Virtual Chassis port from the Virtual Chassis configuration.

You can configure a Virtual Chassis port on either a 1-Gigabit Ethernet (ge) interface or a 10-Gigabit Ethernet (xe) interface. However, you cannot configure a combination of 1-Gigabit Ethernet Virtual Chassis ports and 10-Gigabit Ethernet Virtual Chassis ports in the same Virtual Chassis. We recommend that you configure Virtual Chassis ports only on 10-Gigabit Ethernet interfaces. In addition, to minimize network disruption in the event of a router or link failure, configure redundant Virtual Chassis ports that reside on different line cards in each member router.

Virtual Chassis port interfaces carry both Virtual Chassis Control Protocol (VCCP) packets and internal control and data traffic. Because the internal control traffic is neither encrypted nor authenticated, make sure that the Virtual Chassis port interfaces are properly secured to prevent malicious third-party attacks on the data.

Virtual Chassis ports use a default class-of-service (CoS) configuration that applies equally to all Virtual Chassis port interfaces configured in a Virtual Chassis. Optionally, you can create a customized CoS traffic-control profile and apply it to all Virtual Chassis port interfaces. For example, you might want to create a nondefault traffic-control profile that allocates more than the default 5 percent of the Virtual Chassis port bandwidth to control traffic, or that assigns different priorities and excess rates to different forwarding classes.

Virtual Chassis Port Trunks

If two or more Virtual Chassis ports of the same type and speed are configured between the same two member routers in an MX Series Virtual Chassis, the VCCP software bundles these Virtual Chassis port interfaces into a trunk, reduces the routing cost accordingly, and performs traffic load balancing across all of the Virtual Chassis port interfaces (also referred to as Virtual Chassis port links) in the trunk.

A Virtual Chassis port trunk must include only Virtual Chassis ports of the same type and speed. For example, a Virtual Chassis port trunk can include either all 10-Gigabit Ethernet (xe media type) Virtual Chassis ports or all 1-Gigabit Ethernet (ge media type) Virtual Chassis ports. An MX Series Virtual Chassis does not support a combination of 1-Gigabit Ethernet Virtual Chassis ports and 10-Gigabit Ethernet Virtual Chassis ports in the same Virtual Chassis port trunk.

The router uses the following formula to determine the cost metric of a Virtual Chassis port link in a Virtual Chassis port trunk:

Cost = (300 * 1,000,000,000) / port-speed

where port-speed is the aggegate speed, in bits per second, of the Virtual Chassis port.

For example, a 10-Gigabit Ethernet Virtual Chassis port link has a cost metric of 30 (300 * 1,000,000,000 / 10,000,000,000). A 1-Gigabit Ethernet Virtual Chassis port link has a cost metric of 300 (300 * 1,000,000,000 / 1,000,000,000). Virtual Chassis port links with a lower cost metric are preferred over those with a higher cost metric.

An MX Series Virtual Chassis supports up to 16 Virtual Chassis ports per trunk.

Slot Numbering in the Virtual Chassis

When the Virtual Chassis forms, the slots for line cards (FPCs) that do not host Virtual Chassis ports are renumbered to reflect the slot numbering and offsets used in the Virtual Chassis instead of the physical slot numbers where the line card is actually installed. In a two-member MX Series Virtual Chassis, member 0 in the Virtual Chassis uses FPC slot numbers 0 through 11 with no offset, and member 1 uses FPC slot numbers 12 through 23, with an offset of 12.

For example, a 10-Gigabit Ethernet interface that appears as xe-14/2/2 (FPC slot 14, PIC slot 2, port 2) in the show interfaces command output is actually physical interface xe-2/2/2 (FPC slot 2, PIC slot 2, port 2) on member 1 after deducting the FPC slot numbering offset of 12 for member 1.

The slot numbering for Virtual Chassis ports uses the physical slot number where the Virtual Chassis port is configured. For example, vcp-3/2/0 is configured on physical FPC slot 3, PIC slot 2, port 0.

Virtual Chassis Control Protocol

An MX Series Virtual Chassis is managed by the Virtual Chassis Control Protocol (VCCP), which is a dedicated control protocol based on IS-IS. VCCP runs on the Virtual Chassis port interfaces and performs the following functions in the Virtual Chassis:

  • Discovers and builds the Virtual Chassis topology

  • Runs the primary-role election algorithm to determine the Virtual Chassis primary router

  • Establishes the interchassis routing table to route traffic within the Virtual Chassis

Like IS-IS, VCCP exchanges link-state PDUs for each member router to construct a shortest path first (SPF) topology and to determine each member router’s role (primary or backup) in the Virtual Chassis. Because VCCP supports only point-to-point connections, no more than two member routers can be connected on any given Virtual Chassis port interface.

Member IDs, Roles, and Serial Numbers

To configure an MX Series Virtual Chassis, you must create a preprovisioned configuration that provides the following required information for each member router:

  • Member ID—A numeric value (0 or 1) that identifies the member router in a Virtual Chassis configuration.

  • Role—The role to be performed by each member router in the Virtual Chassis. In a two-member MX Series Virtual Chassis, you must assign both member routers the routing-engine role, which enables either router to function as the primary router or backup router of the Virtual Chassis.

  • Serial number—The chassis serial number of each member router in the Virtual Chassis. To obtain the router’s serial number, find the label affixed to the side of the MX Series chassis, or issue the show chassis hardware command on the router to display the serial number in the command output.

The preprovisioned configuration permanently associates the member ID and role with the member router’s chassis serial number. When a new member router joins the Virtual Chassis, the VCCP software compares the router’s serial number against the values specified in the preprovisioned configuration. If the serial number of a joining router does not match any of the configured serial numbers, the VCCP software prevents that router from becoming a member of the Virtual Chassis.