Understanding EX3300, EX4200, and EX4500 Virtual Chassis Components

Number of Switches per Virtual Chassis

You can interconnect up to six Juniper Networks EX3300 Ethernet Switches in an EX3300 Virtual Chassis

You can interconnect up to ten Juniper Networks EX4200 Ethernet Switches in an EX4200 Virtual Chassis.

Starting in Junos OS Release 11.4, you can interconnect up to ten Juniper Networks EX4500 Ethernet Switches in an EX4500 Virtual Chassis. You can connect up to two EX4500 switches in an EX4500 Virtual Chassis in prior Junos OS releases.

You can interconnect up to ten EX4200 and EX4500 Ethernet Switches in a mixed EX4200 and EX4500 Virtual Chassis. You can interconnect up to nine EX4200 switches in a mixed EX4200 and EX4500 Virtual Chassis. Starting in Junos OS Release 11.4, you can configure up to nine EX4500 switches in a mixed EX4200 and EX4500 Virtual Chassis. You can connect up to two EX4500 switches in a mixed EX4200 and EX4500 Virtual Chassis in prior Junos OS releases.

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.

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 a fiber-optic port as a VCP. You can configure those VCPs on these switches:

• 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
• EX4500 switches, through any SFP+ port

Master Role

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

• Manages the member switches.
• Runs Juniper Networks Junos operating system (Junos OS) for Juniper Networks EX Series Ethernet 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 EX3300, EX4200, or EX4500 switch 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 an EX3300, EX4200, or EX4500 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 EX4200 and EX4500 Virtual Chassis, any switch can be configured in any role in any configuration. If an EX4200 switch is configured in the master role, for instance, an EX4200 switch or an EX4500 switch can be configured in the backup role.

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 an EX3300, EX4200, or EX4500 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 EX4200 and EX4500 Virtual Chassis, any switch can be configured in any role in any configuration. If an EX4200 switch is configured in the master role, for instance, an EX4200 switch or an EX4500 switch can be configured in the backup role.

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 role of linecard, 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 will always be in the linecard role.

Member Switch and Member ID

Each physically discrete EX3300, EX4200, or EX4500 switch is a potential member of a Virtual Chassis configuration. When an EX3300, EX4200, or EX4500 switch is powered on, it receives a member ID that is displayed on the front-panel LCD. 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.

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 performs within the Virtual Chassis configuration by configuring its mastership priority (from 0 to 255). The mastership priority value is the factor with the highest precedence for selecting the master of the Virtual Chassis configuration. A switch with a mastership priority of 0 will never assume the backup or master role.

The default value for mastership priority is 128 for EX3300, EX4200, and EX4500 switches. When a 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 in case the master becomes unavailable. It prevents the original master from preempting control from the backup in situations where the backup has taken control of the Virtual Chassis configuration due to the original master being unavailable.

In a preprovisioned configuration, the mastership priority value is assigned by the software, based on the specified role.

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 status output.