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Understanding EX Series Virtual Chassis Components

Note: This topic applies to all EX Series Virtual Chassis except EX8200 Virtual Chassis. See Understanding EX8200 Virtual Chassis Components for information about EX8200 Virtual Chassis.

This topic describes the components of EX Series Virtual Chassis—including the components of any mixed Virtual Chassis that contains EX series member switches—except EX8200 Virtual Chassis.

This topic covers:

Maximum Number of Switches per Virtual Chassis

The maximum number of switches that a Virtual Chassis supports varies by Virtual Chassis and can depend on the Junos OS release running on the Virtual Chassis. Table 1 lists the maximum member switch support by Virtual Chassis and Junos OS release.

Virtual Chassis Ports (VCPs)

You use Virtual Chassis ports (VCPs) to interconnect the member switches in a Virtual Chassis.

Some switches have dedicated VCPs. Dedicated VCPs allow you to interconnect switches without requiring any additional interface configuration.

These switches have dedicated VCPs:

• EX4200 switches, on the rear panel
• EX4500 switches, on the Virtual Chassis module
• EX4550 switches, on the Virtual Chassis module

To interconnect switches that do not have dedicated VCPs or to interconnect switches across greater distances than allowed by a dedicated-VCP connection, you configure an optical port as a VCP. You can configure those VCPs on these switches:

• EX2200 switches, through an uplink port

  Note: All RJ-45 interfaces, including built-in network ports with 10/100/1000BASE-T Gigabit Ethernet connectors and 1000BASE-T RJ-45 transceivers, on EX2200 and EX2200-C switches, can also be configured into VCPs.

• EX3300 switches, through an uplink port

  Note: Uplink ports 2 and 3 on EX3300 switches are configured as VCPs by default.

• EX4200 switches, through uplink module ports (SFP, SFP+, or XFP) or through an SFP+ port on the EX4200-24F switch
• EX4300 switches, through uplink ports

  Note: All QSFP+ ports on an EX4300 switch are configured as VCPs by default.

• EX4500 switches, through any SFP+ port
• EX4550 switches, through any SFP+ port
• EX4600 switches, through SFP+ and QSFP+ ports.

All supported SFP, SFP+, and XFP uplink connections between EX4200, EX4500, and EX4550 switches can be configured as VCPs.

You can increase the Virtual Chassis bandwidth between member switches by configuring multiple optical ports connecting the switches as VCPs. The optical ports configured as VCPs automatically form a Link Aggregation Group (LAG) bundle. See Understanding EX Series Virtual Chassis Port Link Aggregation.

Master Role

The member that functions in the master role in the Virtual Chassis:

• Manages the member switches.
• Runs Junos OS for EX Series switches in a master role.
• Runs the chassis management processes and control protocols.
• Represents all the member switches interconnected within the Virtual Chassis configuration. (The hostname and other properties that you assign to this switch during setup apply to all members of the Virtual Chassis configuration.)

When an EX Series switch that supports Virtual Chassis is powered on as a standalone switch, it is considered the master member. In a Virtual Chassis, one member functions as the master and a second member functions as the backup:

• In a preprovisioned configuration, one of the two members assigned as routing-engine functions as the master member. The selection of which member assigned as routing-engine functions as master and which as backup is determined by the software based on the master election algorithm. See Understanding How the Master in a Virtual Chassis Is Elected.
• In a configuration that is not preprovisioned, the selection of the master and backup is determined by the mastership priority value and secondary factors in the master election algorithm.

In a mixed EX4300 and EX4600 Virtual Chassis, an EX4600 switch must assume the master role.

In any mixed Virtual Chassis configuration that includes EX4200 switches, EX4500 switches, or EX4550 switches, any switch can be configured in any role in any configuration.

Backup Role

The member that functions in the backup role in the Virtual Chassis:

• Maintains a state of readiness to take over the master role if the master fails.
• Runs Junos OS for EX Series switches in a backup role.
• Synchronizes with the master in terms of protocol states, forwarding tables, and so forth, so that it is prepared to preserve routing information and maintain network connectivity without disruption in case the master is unavailable.

You must have at least two member switches in the Virtual Chassis configuration in order to have a backup member.

• In a preprovisioned configuration, one of the two members assigned as routing-engine functions in the backup role. The selection of which member assigned as routing-engine functions as master and which as backup is determined by the software based on the master election algorithm. See Understanding How the Master in a Virtual Chassis Is Elected.
• In a configuration that is not preprovisioned, the selection of the master and backup is determined by the mastership priority value and secondary factors in the master election algorithm.

In a mixed EX4300 and EX4600 Virtual Chassis, we strongly recommend configuring an EX4600 switch into the backup role. A mixed EX4300 and EX4600 Virtual Chassis must use an EX4600 member switch in the master role, and configuring an EX4600 switch into the backup role ensures that the Virtual Chassis remains up after a switchover event.

In any mixed Virtual Chassis configuration that includes EX4200 switches, EX4500 switches, or EX4550 switches, any switch can be configured in any role in any configuration.

Linecard Role

A member that functions in the linecard role in the Virtual Chassis:

• Runs only a subset of Junos OS for EX Series switches.
• Does not run the chassis control protocols.
• Can detect certain error conditions (such as an unplugged cable) on any interfaces that have been configured on it through the master.

The Virtual Chassis configuration must have at least three members in order to include a linecard member.

• In a preprovisioned configuration, you can explicitly configure a member with the linecard role, which makes it ineligible for functioning as a master or backup.
• In a configuration that is not preprovisioned, the members that are not selected as master or backup function as linecard members of the Virtual Chassis configuration. The selection of the master and backup is determined by the mastership priority value and secondary factors in the master election algorithm. A switch with a mastership priority of 0 is always in the linecard role.

Member Switch and Member ID

Each standalone EX Series switch that supports Virtual Chassis is a potential member of a Virtual Chassis configuration. When one of those switches is powered on, it receives a member ID that can be seen by viewing the front-panel LCD or by entering the show virtual-chassis command. If the switch is powered on as a standalone switch, that member’s member ID is always 0. When the switch is interconnected with other switches in a Virtual Chassis configuration, its member ID is assigned by the master based on various factors, such as the order in which the switch was added to the Virtual Chassis configuration or the member ID assigned by a preprovisioned configuration. See Understanding How the Master in a Virtual Chassis Is Elected.

If the Virtual Chassis configuration previously included a member switch and that member was physically disconnected or removed from the Virtual Chassis configuration, its member ID is not available for assignment as part of the standard sequential assignment by the master. For example, you might have a Virtual Chassis configuration composed of member 0, member 2, and member 3, because member 1 was removed. When you add another member switch and power it on, the master assigns it as member 4.

The member ID distinguishes the member switches from one another. You use the member ID:

• To assign a mastership priority value to a member switch
• To configure interfaces for a member switch (The function is similar to that of a slot number on Juniper Networks routers.)
• To apply some operational commands to a member switch
• To display status or characteristics of a member switch

Mastership Priority

In a configuration that is not preprovisioned, you can designate the role (master, backup, or linecard) that a member switch assumes by configuring its mastership priority (from 0 through 255). The mastership priority value is the factor in the master election algorithm with the highest precedence for selecting the master of the Virtual Chassis configuration. A switch with a mastership priority of 0 never assumes the backup or master role.

The default value for mastership priority is 128 for EX2200, EX3300, EX4200, EX4500, EX4550, and EX4600 switches. When a standalone switch is powered on, it receives the default mastership priority value. Because it is the only member of the Virtual Chassis configuration, it is also the master. When you interconnect a standalone switch to an existing Virtual Chassis configuration (which implicitly includes its own master), we recommend that you explicitly configure the mastership priority of the members that you want to function as the master and backup.

Note: Configuring the same mastership priority value for both the master and backup helps to ensure a smooth transition from master to backup when the master becomes unavailable. It prevents the original master from preempting control from the backup when the backup has taken control of the Virtual Chassis configuration because the original master became unavailable.

In a preprovisioned configuration, you assign the role of each member switch. An EX9200 switch does not have a mastership priority and an EX9200 Virtual Chassis, therefore, must be preprovisioned.

Mixed Virtual Chassis

EX4200 switches, EX4500 switches, and EX4550 switches can be interconnected into the same Virtual Chassis to form a mixed EX4200 and EX4500 Virtual Chassis, mixed EX4200 and EX4550 Virtual Chassis, mixed EX4500 and EX4550 Virtual Chassis, or mixed EX4200, EX4500, and EX4550 Virtual Chassis. The mixed Virtual Chassis supports up to 10 member switches regardless of whether the switches are EX4200 switches, EX4500 switches, or EX4550 switches. Any model of EX4200, EX4500, or EX4550 switch can be interconnected into the same mixed Virtual Chassis. The master election process that decides member switch roles in a mixed Virtual Chassis is identical to the master election process in a non-mixed Virtual Chassis, so any member switch in a mixed Virtual Chassis can assume the master, backup, or linecard role.

EX4300 and EX4600 switches can act as member switches in a mixed EX4300 and EX4600 Virtual Chassis. An EX4600 switch must assume the master role in a mixed EX4300 and EX4600 Virtual Chassis. We strongly recommend configuring EX4600 switches only into the Routing Engine role when you are configuring a mixed EX4300 and EX4600 Virtual Chassis to ensure only EX4600 switches assume the master role.

EX2200 and EX3300 switches cannot be a part of any mixed Virtual Chassis.

Virtual Chassis Identifier (VCID)

All members of a Virtual Chassis configuration share one Virtual Chassis identifier (VCID). This identifier is derived from internal parameters. When you are monitoring a Virtual Chassis configuration, the VCID is displayed in certain interface views and is also part of the show virtual-chassis output.