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Understanding Virtual Chassis Components

 

This topic describes the components of an EX series or a QFX Series Virtual Chassis.

  • An EX Series Virtual Chassis is a supported combination of standalone EX Series switches interconnected and managed as a single chassis. 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.

    Note

    We do not recommend using EX9200 switches in a Virtual Chassis, and we phased out support for that architecture as of Junos OS Release 17.1R1. For deployments with EX9200 switches, we recommend planning or moving to MC-LAG or Junos Fusion Enterprise architectures instead of using a Virtual Chassis.

  • A QFX Series Virtual Chassis is a supported combination of standalone QFX3500, QFX3600, QFX5100, QFX5110, QFX5120, or QFX5200 switches interconnected and managed as a single chassis. EX4650 Virtual Chassis operate the same as QFX5120 Virtual Chassis, so information in this topic about QFX Series Virtual Chassis applies similarly to an EX4650 Virtual Chassis.

    Note

    EX4300 switches (excluding multigigabit models [EX4300-48MP]) can also be interconnected into a mixed Virtual Chassis with QFX3500, QFX3600, and QFX5100 switches.

This topic does not describe Virtual Chassis Fabric components. Instead, see Understanding Virtual Chassis Fabric Components.

Maximum Switch Support

The maximum number of switches that a Virtual Chassis supports varies by Virtual Chassis and might also depend on the Junos OS release running on the Virtual Chassis.

Maximum Number of Switches in an EX Series Virtual Chassis

Table 1 lists the maximum number of member switches supported in an EX Series Virtual Chassis by Junos OS release.

Table 1: Maximum Member Switch Support for EX Series Virtual Chassis by Junos OS Release

Type of EX Series Virtual Chassis

Maximum Member Switches by Junos OS Release

EX2200 Virtual Chassis

12.2R1—Initial release. Up to 4 EX2200 member switches.

EX2300 Virtual Chassis

15.1X53-D50—Initial release. Up to 4 EX2300 member switches.

18.1R2—Up to 4 multigigabit EX2300 (EX2300-24MP and EX2300-48MP) member switches.

18.4R1—Starting in Junos OS Release 18.4R1, up to 4 of any model EX2300 member switches (including multigigabit models and any other EX2300 switches) can be combined in the same Virtual Chassis.

EX3300 Virtual Chassis

11.3R1—Initial release. Up to 6 EX3300 member switches.

12.2R1—Starting in Junos OS Release 12.2R1, an EX3300 Virtual Chassis can support up to 10 EX3300 member switches.

EX3400 Virtual Chassis

15.1X53-D50—Initial release. Up to 10 EX3400 member switches.

EX4200 Virtual Chassis

9.0R1—Initial release. Up to 10 EX4200 member switches.

EX4300 Virtual Chassis

13.2X50-D10—Initial release. Up to 10 EX4300 member switches.

13.2X50-D20—Starting in Junos OS Release 13.2X50-D20, a mixed QFX Series Virtual Chassis or VCF can also contain EX4300 switches.

18.2R1—Starting in Junos OS Release 18.2R1 with the introduction of EX4300 multigigabit model switches (EX4300-48MP), an EX4300 Virtual Chassis can contain up to 10 EX4300 multigigabit model switches as a non-mixed Virtual Chassis or a combination of EX4300 multigigabit model switches with other EX4300 switches as a mixed EX4300 Virtual Chassis.

EX4500 Virtual Chassis

11.1R1—Initial release. Support for up to 2 EX4500 member switches.

11.4R1—Support for up to 10 EX4500 member switches.

EX4550 Virtual Chassis

12.2R1—Initial release. Support for up to 10 EX4550 member switches.

EX4600 Virtual Chassis

13.2X51-D25—Initial release. Support for up to 10 EX4600 member switches.

EX4650 Virtual Chassis

19.3R1—Initial release. Up to 2 EX4650 switches in Routing Engine roles only.

20.1R1—Starting in Junos OS Release 20.1R1, an EX4650 Virtual Chassis can have up to 4 members.

Mixed EX4200 and EX4500 Virtual Chassis

11.1R1—Initial release. Up to 2 EX4500 member switches and up to 8 EX4200 member switches.

11.2R1—Up to 9 EX4200 member switches.

11.4R1—Up to 9 EX4500 member switches.

Mixed EX4200 and EX4550 Virtual Chassis

12.2R1—Initial release. Up to 10 total EX4200 and EX4550 member switches.

Mixed EX4200, EX4500, and EX4550 Virtual Chassis

12.2R1—Initial release. Up to 10 total EX4200, EX4500, and EX4550 member switches.

Mixed EX4300 and EX4600 Virtual Chassis

13.2X51-D25—Initial release. Up to 10 total EX4300 and EX4600 member switches. EX4600 member witches must assume Routing Engine role.

Note: EX4300 multigigabit model (EX4300-48MP) switches are not supported in a mixed Virtual Chassis with EX4600 switches.

Mixed EX4500 and EX4550 Virtual Chassis

12.2R1—Initial release. Up to 10 total EX4500 and EX4550 switches.

EX9200 Virtual Chassis

13.2R2—Initial release. Up to 2 EX9200 switches.

Note: We have phased out support for EX9200 switches in a Virtual Chassis as of Junos OS Release 17.1R1. For deployments with EX9200 switches, we recommend planning or moving to MC-LAG or Junos Fusion Enterprise architectures instead of using a Virtual Chassis configuration.

Maximum Number of Switches in a QFX Series Virtual Chassis (Including Mixed Virtual Chassis with EX Series Switches)

Table 2 lists the maximum number of member switches supported in a QFX Series Virtual Chassis by Junos OS release, including mixed QFX Series Virtual Chassis with EX Series switch members.

Table 2: Maximum Member Switch Support for QFX Series Virtual Chassis by Junos OS Release

Type of QFX Series Virtual Chassis

Maximum Member Switches by Junos OS Release

QFX3500 or QFX3600 Virtual Chassis:

  • Only QFX3500 and QFX3600 switches in any combination.

13.2X50-D15—Initial release. Up to 10 total member switches.

QFX3500 or QFX3600 mixed-mode Virtual Chassis:

  • QFX3500 and QFX3600 switches in Routing Engine role with any combination of QFX3500, QFX3600, and EX4300 switches (excluding EX4300 multigigabit models) in linecard role.

13.2X51-D20—Up to 10 total member switches.

QFX5100 Virtual Chassis:

  • Only QFX5100 switches.

13.2X51-D20—Initial release. Up to 10 member switches (except QFX5100-96S).

13.2X51-D20—Initial release for QFX5100-96S. Up to 4 member switches.

13.2X53-D25—Prior to Junos OS Release 13.2X51-D25, only up to 4 member switches can be in a QFX5100 Virtual Chassis. Starting in Junos OS Release 13.2X51-D25, you can include up to 10 QFX5100-96S switches in a mixed or non-mixed QFX5100 Virtual Chassis.

QFX5100 mixed-mode Virtual Chassis:

  • QFX5100 switches in Routing Engine role with any combination of QFX5100, QFX3500, QFX3600, and EX4300 switches (excluding EX4300 multigigabit models) in linecard role.

13.2X51-D20—Initial release. Up to 10 total member switches (except QFX5100-96S).

13.2X53-D25—Up to 10 total member switches (including QFX5100-96S).

QFX5110 Virtual Chassis:

  • QFX5110 switches in Routing Engine role with any combination of supported QFX5110 and QFX5100 switches in linecard role.

17.3R1—Initial release. Up to 10 member switches.

QFX5120 Virtual Chassis:

19.3R1—Initial release on QFX5120-48Y switches. Up to 2 member switches, both in Routing Engine role.

20.2R1—Initial release on QFX5120-48T switches. Up to 2 member switches, both in Routing Engine role.

QFX5200 Virtual Chassis—

  • Only QFX5200 switches.

17.3R2 and 17.4R1—Initial release. Up to 3 member switches.

Virtual Chassis Ports (VCPs)

You set up a Virtual Chassis by configuring Virtual Chassis ports (VCPs) on the member switches, and interconnecting the switches using the VCPs. VCPs are responsible for passing all data and control traffic between member switches in the Virtual Chassis.

Virtual Chassis Port Options

Some switches have dedicated VCPs; you can only use these ports as VCPs and you can’t reconfigure them as network ports. Dedicated VCPs allow you to interconnect switches into a Virtual Chassis without requiring any additional interface configuration.

Some switches have ports that are configured as VCPs by default. You don’t need to explicitly configure those as VCPs to use them to interconnect the switches into a Virtual Chassis.

Most switches have optical or uplink ports that you can also configure as VCPs.

You must configure VCPs to interconnect switches that do not have dedicated or default-configured VCPs or to interconnect switches across greater distances than allowed by a dedicated VCP connection. Otherwise, you can mix any of the supported VCP options among the members of a Virtual Chassis, and we recommend having redundant links between any two members for resiliency or to increase member communication bandwidth. VCPs automatically bundle into a Link Aggregation Group when two or more ports operating at the same speed are configured into VCPs between the same two member switches. See Understanding Virtual Chassis Port Link Aggregation for details.

When adding switches to an existing Virtual Chassis or adding new redundant links between existing members, if the automatic VCP conversion feature is enabled, under the right conditions the ports on both sides of the connection will convert into VCPs automatically (see Automatic Virtual Chassis Port (VCP) Conversion).

Table 3 summarizes the available VCP options on switches in an EX Series or QFX Series Virtual Chassis. For complete details on where dedicated VCPs, default-configured VCPs, or ports that can be configured as VCPs are located on a switch, and the supported transceivers and cables that you can use for VCP connections on the switch, see the hardware documentation for that type of switch.

Table 3: VCP Options by Switch Type

Switch

Dedicated VCPs

Default VCPs

Ports that can be configured and are supported as VCPs

EX2200

None

None

Any uplink ports

All RJ-45 interfaces, including built-in network ports with 10/100/1000BASE-T Gigabit Ethernet connectors and 1000BASE-T RJ-45 transceivers

EX2300 (including multigigabit EX2300 models)

None

None

10-Gigabit Ethernet uplink ports with SFP+ tranceivers

Note: You cannot use ports with SFP transceivers as VCPs on EX2300 switches to form a Virtual Chassis.

EX3300

None

Uplink ports 2 and 3

Any of the 4 uplink ports (ports 0 through 3)

EX3400

None

All QSFP+ uplink ports (PIC slot 1, ports 0 and 1)

Any SFP+ uplink ports

Note: You cannot use ports with SFP transceivers as VCPs on EX3400 switches to form a Virtual Chassis.

EX4200

2 ports on rear panel

None

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

Note: You cannot set a 1000BASE-T copper SFP transceiver (EX-SFP-1GE-T) connection as a VCP on EX4200 switches.

EX4300

None

All QSFP+ ports

Any uplink ports installed with SFP+ or QSPF+ transceivers

Note: On 32-port EX4300 switches, you can’t use the four built-in 10-Gigabit Ethernet SFP+ ports as VCPs.

EX4300 Multigigabit Models (EX4300-48MP)

4 40-Gbps QSFP+ ports on rear panel

None

None

EX4500 and EX4550

Two ports on the Virtual Chassis module

None

Any SFP, SFP+, or XFP uplink module port

Note: You cannot use SFP+ uplink ports installed with 1000BASE-T copper SFP transceivers (EX-SFP-1GE-T) as VCP connections on EX4500 and EX4550 switches.

EX4600

None

None

Any SFP+ and QSFP+ ports

EX4650

None

None

Any of the 40-Gigabit Ethernet or 100-Gigabit QSFP28 ports on the front panel (ports 48 through 55), non-channelized

Note: The Junos OS doesn’t prevent you from trying to set other ports as VCPs, but they don’t operate properly as VCPs.

QFX3500 and QFX3600

None

None

Any non-channelized 40-Gigabit Ethernet QSFP+ interfaces

QFX5100

None

None

Any non-channelized 40-Gigabit Ethernet QSFP+ interfaces

QFX5110

None

None

Any 40-Gigabit Ethernet or 100-Gigabit Ethernet QSFP28 ports

Any non-channelized 40-Gigabit Ethernet QSFP+ interfaces

Any non-channelized 10-Gigabit Ethernet SFP+ interfaces (on QFX5110 switch models that support these ports)

QFX5120

None

None

(QFX5120-48Y) Any of the eight 40-Gigabit Ethernet or 100-Gigabit Ethernet QSFP+ or QSFP28 ports on the front panel (ports 48 through 55), non-channelized

(QFX5120-48T) Any of the six 40-Gigabit Ethernet or 100-Gigabit Ethernet QSFP+ or QSFP28 ports on the front panel (ports 48 through 53), non-channelized

Note: The Junos OS doesn’t prevent you from trying to set other ports on QFX5120 switches as VCPs, but they don’t operate properly as VCPs.

QFX5200

None

None

Any 40-Gigabit Ethernet QSFP+ ports

Starting in Junos OS Release 17.3R2-S4, you can also use 100-Gigabit Ethernet QSFP28 ports as VCPs on QFX5200 switches.

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

QSFP+ interfaces that have been channelized into SFP+ interfaces using a breakout cable cannot be configured into VCPs.

Automatic Virtual Chassis Port (VCP) Conversion

When the automatic VCP conversion feature is enabled and you cable a new link from a new switch being added into an existing Virtual Chassis, or add a redundant link between two members of a Virtual Chassis, ports that can be VCPs are automatically converted into VCPs under the following conditions:

  • Link Layer Discovery Protocol (LLDP) or LLDP-Media Endpoint Discovery (LLDP-MED) is enabled on the interfaces for the members on both ends of the new link. The two sides exchange LLDP packets to accomplish the port conversion.

  • The Virtual Chassis must be preprovisioned with the switches on both sides of the link already configured in the members list of the Virtual Chassis using the set virtual-chassis member command.

  • The interfaces for the ports on both ends of the link are not already configured as VCPs. Both sides of the link must be in the same state to handshake and establish the VCP link.

Using automatic VCP conversion when adding a switch to a preprovisioned Virtual Chassis is also called autoprovisioning the new member.

For ports to be eligible for automatic VCP conversion, you must convert them back into network ports using the request virtual-chassis vc-port delete command if they are default-configured VCPs or you previously configured them into VCPs. Switches do not automatically convert VCPs back into network ports when you remove them from a Virtual Chassis and disconnect the links.

Automatic VCP conversion is enabled by default on all Virtual Chassis, except in the following cases:

  • Starting in Junos OS Releases 15.1R7 and 14.1X53-D47, in EX2200, EX3300, EX4200, EX4500, and EX4550 Virtual Chassis, automatic VCP conversion is disabled by default. If desired, you can enable the feature by configuring the auto-conversion statement at the [edit virtual-chassis] hierarchy level on the Virtual Chassis.

    Caution

    When automatic VCP conversion is enabled in a Virtual Chassis with switches that have dedicated VCPs (EX4200, EX4500, or EX4550 Virtual Chassis), if network or uplink ports are automatically converted into VCPs to create a redundant link with a dedicated VCP connection between the same two Virtual Chassis members, you must reboot the Virtual Chassis to avoid creating a traffic loop within the Virtual Chassis. (The same issue can happen even if you manually convert the ports into VCPs to create the redundant VCP link with a dedicated VCP link, so you must also reboot the Virtual Chassis in that case to avoid traffic looping.)

  • Starting in Junos OS Releases 14.1X53-D47, 17.4R2, 18.1R3, 18.2R2, and 18.3R1 for EX4300, EX4600, QFX Series Virtual Chassis and for any EX4650 and QFX5120 Virtual Chassis (which all have the automatic VCP conversion feature enabled by default), you can choose to disable the feature by configuring no-auto-conversion at the [edit virtual-chassis] hierarchy level on the Virtual Chassis. To return to the default behavior to re-enable automatic VCP conversion, delete the no-auto-conversion statement from the configuration.

Virtual Chassis Port Link Aggregation Groups

You can increase VCP bandwidth between member switches by configuring multiple links between the same two switches into VCP links. When multiple VCPs interconnect the same two member switches, the links automatically form a Link Aggregation Group (LAG) bundle if the VCP links are the same speed. For example, if you have two 40-Gbps QSFP+ VCP links connected between member switches, the links automatically form a LAG with 80-Gbps total bandwidth. However, 10-Gigabit SFP+ and 40-Gbps QSFP+ VCP links will not become members of the same LAG.

Within a Virtual Chassis, you can also configure network interfaces located on different Virtual Chassis member switches to form a LAG, which provides load-balancing and redundancy for network traffic that the Virtual Chassis forwards. See Understanding Virtual Chassis Port Link Aggregation for details on the difference between VCP LAGs and network interface LAGs within a Virtual Chassis.

Master Routing Engine Role

In a Virtual Chassis, each member switch operates in one of two roles, Routing Engine role or linecard role. When in Routing Engine role, a member switch acts as the master or backup Routing Engine.

The master Routing Engine member in the Virtual Chassis:

  • Manages the member switches.

  • Runs Junos OS for the switches as a master Routing Engine.

  • 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.)

In a preprovisioned configuration, the Virtual Chassis master election algorithm determines which member switch in the Routing Engine role acts as the Virtual Chassis master and which acts as the backup. See Understanding How the Master in a Virtual Chassis Is Elected.

In a configuration that is not preprovisioned, called a nonprovisioned configuration, the Virtual Chassis selects the master and backup using the mastership priority value and secondary factors in the master election algorithm.

The remaining switches in the Virtual Chassis that are not the master or backup operate in the linecard role.

Use the following guidelines for assigning Routing Engine roles to the switches in a mixed Virtual Chassis:

  • In any mixed Virtual Chassis configuration that includes EX4200 switches, EX4500 switches, or EX4550 switches, you can configure any switch in any role in any configuration.

  • In a mixed EX4300 Virtual Chassis composed of EX4300 multigigabit model (EX4300-48MP) and other EX4300 model switches, you should always have EX4300 multigigabit model switches in the Routing Engine role.

  • In a mixed EX4600 Virtual Chassis with EX4300 switches, EX4600 switches are always in the master Routing Engine role.

  • In a mixed QFX Series Virtual Chassis made up of QFX5100 switches with QFX3500, QFX3600, or EX4300 switches, we recommend configuring QFX5100 switches into the Routing Engine role.

  • In a mixed QFX Series Virtual Chassis made up of QFX3500, QFX3600, and EX4300 switches, we recommend configuring QFX3500 or QFX3600 switches into the master and backup Routing Engine roles.

  • In a QFX5110 Virtual Chassis with QFX5110 and QFX5100 switches, we recommend configuring only QFX5110 switches into the Routing Engine role.

  • In a two-member EX4650 or QFX5120 Virtual Chassis, configure both member switches into the Routing Engine role as master and backup member switches only (no linecard role members).

Backup Routing Engine Role

The member that functions in the backup Routing Engine role in a Virtual Chassis:

  • Maintains a state of readiness to take over the master Routing Engine role if the master fails.

  • Runs Junos OS for the switches as a backup Routing Engine.

  • Synchronizes with the master in terms of protocol states, forwarding tables, and other information, so that it is prepared to preserve routing information and maintain network connectivity without disruption in case the master is unavailable.

The Virtual Chassis configuration must have at least two member switches in order to have a backup Routing Engine member.

In a preprovisioned configuration, the Virtual Chassis master election algorithm determines which member switch in the Routing Engine role acts as the Virtual Chassis master and which acts as the backup. See Understanding How the Master in a Virtual Chassis Is Elected.

In a nonprovisioned configuration, the Virtual Chassis selects the master and backup member switches using the mastership priority value and secondary factors in the master election algorithm.

Use the following guidelines for assigning Routing Engine roles to the switches in a mixed Virtual Chassis:

  • In any mixed Virtual Chassis configuration that includes EX4200 switches, EX4500 switches, or EX4550 switches, you can configure any switch in any role in any configuration.

  • In a mixed EX4300 Virtual Chassis composed of EX4300 multigigabit model (EX4300-48MP) and other EX4300 model switches, you should always have EX4300 multigigabit model switches in the master and backup Routing Engine roles.

  • In a mixed EX4600 Virtual Chassis with EX4300 switches, you must use an EX4600 switch in the master role, and we strongly recommend you also configure an EX4600 switch into the backup role to help the Virtual Chassis remain stable when a routing engine switchover happens.

  • In a mixed QFX Series Virtual Chassis made up of QFX5100 switches with QFX3500, QFX3600, or EX4300 switches, we recommend configuring the QFX5100 switches into the Routing Engine role.

  • In a mixed QFX Series Virtual Chassis made up of QFX3500, QFX3600, and EX4300 switches, we recommend configuring only QFX3500 or QFX3600 switches into the master and backup Routing Engine roles.

  • In a QFX5110 Virtual Chassis with QFX5110 and QFX5100 switches, we recommend configuring only QFX5110 switches into the Routing Engine role.

  • In a two-member EX4650 or QFX5120 Virtual Chassis, configure both member switches into the Routing Engine role as master and backup member switches only (no linecard role members).

Linecard Role

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

  • Runs only a subset of Junos OS.

  • 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 means it can’t be a master or backup Routing Engine.

In a nonprovisioned configuration, the members that are not selected as master or backup operate as linecard members of the Virtual Chassis. The Virtual Chassis selects the master and backup member switches using 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.

In any two-member Virtual Chassis, for high availability you should configure both members into the Routing Engine role, and no members in the linecard role. Otherwise, in a Virtual Chassis with more than two members, any supported switch type can operate in linecard role.

Use the following guidelines for assigning Routing Engine and linecard roles to the switches in a QFX Series Virtual Chassis:

  • In a mixed QFX Series Virtual Chassis made up of QFX5100 switches with QFX3500, QFX3600, or EX4300 switches, we recommend configuring the QFX5100 switches into the Routing Engine role. In a mixed QFX Series Virtual Chassis that does not contain QFX5100 switches, we recommend configuring QFX3500 or QFX3600 switches into the Routing Engine role.

  • In a QFX5110 Virtual Chassis made up of QFX5110 and QFX5100 switches, we recommend configuring only QFX5110 switches into the Routing Engine role.

Member Switch and Member ID

Each standalone switch that supports Virtual Chassis is a potential member of a Virtual Chassis configuration. When you power on one of those switches, it has a Virtual Chassis member ID that you can see on the front-panel LCD on some switches or in show virtual-chassis command output. If the switch is powered on as a standalone switch, its member ID is always 0. When you interconnect the switch into a Virtual Chassis configuration, the master member switch assigns it a member ID based on various factors such as the order in which the switch was added to the Virtual Chassis or if you defined member IDs based on switch serial numbers in the preprovisioning process.

If the Virtual Chassis configuration previously included a member switch and you physically disconnected or removed that member from the Virtual Chassis configuration, its member ID is not automatically available for assignment as part of the master’s standard sequential member ID assignment. For example, you might have a Virtual Chassis configuration with 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 ID 4 to it, not ID 1. If you want to reuse a member ID from a member switch that was removed, you can recycle the member id (see the request virtual-chassis recycle command for details). .

The member ID distinguishes the member switches from each other. You use the member ID to:

  • assign a mastership priority value to a member switch.

  • configure interfaces for a member switch, similar to specifying a juniper Networks device slot number.

  • apply some operational commands to a member switch.

  • display status or characteristics of a member switch.

Mastership Priority

In a nonprovisioned configuration, you can designate the role (master or backup Routing Engine role or linecard role) that a member switch assumes by configuring its mastership priority (a number from 0 through 255). The mastership priority value is the first consideration in the master election algorithm for selecting the master of the Virtual Chassis configuration. A switch with a mastership priority of 0 never assumes the backup or master Routing Engine role.

When you power on a standalone switch, it has the default mastership priority value 128. Because it’s the only member switch in its own Virtual Chassis configuration, it’s also the master member. When you interconnect a standalone switch to an existing Virtual Chassis configuration (which has 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 if 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 always assign the role of each member switch.

Virtual Chassis Identifier (VCID)

All members of a Virtual Chassis configuration share one Virtual Chassis identifier (VCID). The Virtual Chassis derives this identifier from internal parameters. When you monitor a Virtual Chassis configuration, certain interface views and the show virtual-chassis command display the VCID.

Nonvolatile Storage in a Virtual Chassis

EX Series and QFX Series switches store Junos OS system files in internal flash memory. In Virtual Chassis configurations, both the master and the backup switch store the configuration information for all the member switches.

Junos OS optimizes the way a Virtual Chassis stores its configuration if a member switch or the Virtual Chassis configuration shuts down improperly, as follows:

  • If the master is not available, the backup switch takes on the role of the master and its internal flash memory takes over as the alternate location for maintaining nonvolatile configuration memory.

  • If you take a member switch offline for repair, the master stores the configuration of the member switch.

Note

File storage management differs in an EX8200 Virtual Chassis; see Understanding File Storage in an EX8200 Virtual Chassis for details.

Release History Table
Release
Description
Starting in Junos OS Release 20.1R1, an EX4650 Virtual Chassis can have up to 4 members.
Starting in Junos OS Release 18.4R1, up to 4 of any model EX2300 member switches (including multigigabit models and any other EX2300 switches) can be combined in the same Virtual Chassis.
Starting in Junos OS Release 18.2R1 with the introduction of EX4300 multigigabit model switches (EX4300-48MP), an EX4300 Virtual Chassis can contain up to 10 EX4300 multigigabit model switches as a non-mixed Virtual Chassis or a combination of EX4300 multigigabit model switches with other EX4300 switches as a mixed EX4300 Virtual Chassis.
Starting in Junos OS Release 17.3R2-S4, you can also use 100-Gigabit Ethernet QSFP28 ports as VCPs on QFX5200 switches.
Starting in Junos OS Releases 15.1R7 and 14.1X53-D47, in EX2200, EX3300, EX4200, EX4500, and EX4550 Virtual Chassis, automatic VCP conversion is disabled by default.
Starting in Junos OS Releases 14.1X53-D47, 17.4R2, 18.1R3, 18.2R2, and 18.3R1 for EX4300, EX4600, QFX Series Virtual Chassis and for any EX4650 and QFX5120 Virtual Chassis (which all have the automatic VCP conversion feature enabled by default), you can choose to disable the feature by configuring no-auto-conversion at the [edit virtual-chassis] hierarchy level on the Virtual Chassis.
Starting in Junos OS Release 13.2X51-D25, you can include up to 10 QFX5100-96S switches in a mixed or non-mixed QFX5100 Virtual Chassis.
Starting in Junos OS Release 13.2X50-D20, a mixed QFX Series Virtual Chassis or VCF can also contain EX4300 switches.
Starting in Junos OS Release 12.2R1, an EX3300 Virtual Chassis can support up to 10 EX3300 member switches.