Rate and give feedback:  Feedback Received. Thank You!

Rate and give feedback: 

X

This document helped resolve my issue

Yes No

Additional Comments

800 characters remaining

May we contact you if necessary?

Name:  

E-mail: 

Enter a valid Email ID

Need product assistance? Contact Juniper Support

Submit

This site is protected by hCaptcha and its Privacy Policy and Terms of Service apply.

English  

English

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 EX4200, EX4500, or EX4550 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 also depends 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 a fiber-optic port as a VCP. You can configure those VCPs on these switches:

• EX2200 switches, through an uplink port
• 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
• EX4550 switches, through any SFP+ port

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

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 EX2200, EX3300, EX4200, EX4500, or EX4550 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 EX Series 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 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 an EX Series 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 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 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 standalone EX2200, EX3300, EX4200, EX4500, or EX4550 switch 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 an EX Series 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 to 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 will never assume the backup or master role.

The default value for mastership priority is 128 for EX2200, EX3300, EX4200, EX4500, and EX4550 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.

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.