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 support for that architecture was phased out 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, or QFX5200 switches interconnected and managed as a single chassis. 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 discuss Virtual Chassis Fabric components. For information on Virtual Chassis Fabric components, 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 member switch support by EX Series Virtual Chassis and Junos OS release.

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

Maximum Member Switch Support

Initial Junos OS Release

EX2200 Virtual Chassis

12.2R1—Initial release. Support for up to four EX2200 member switches.

EX2300 Virtual Chassis

15.1X53-D50—Initial release. Support for up to four EX2300 member switches.

18.1R2—Support for up to four multigigabit EX2300 (EX2300-24MP and EX2300-48MP) member switches.

18.4R1—Starting in Junos OS Release 18.4R1, up to four 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. Support for up to six EX3300 member switches

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

EX3400 Virtual Chassis

15.1X53-D50—Initial release. Support for up to ten EX3400 member switches

EX4200 Virtual Chassis

9.0R1—Initial release. Support for up to ten EX4200 member switches

EX4300 Virtual Chassis

13.2X50-D10—Initial release. Support for up to ten EX4300 member switches

13.2X50-D20—Starting in Junos OS Release 13.2X50-D20, EX4300 switch support was added in a mixed QFX Series Virtual Chassis or in a VCF.

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 ten 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 two EX4500 switches

11.4R1—Support for up to ten EX4500 member switches

EX4550 Virtual Chassis

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

EX4600 Virtual Chassis

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

Mixed EX4200 and EX4500 Virtual Chassis

11.1R1—Initial release. Support for up to two EX4500 switches and up to eight EX4200 switches

11.2R1—Support for up to nine EX4200 switches

11.4R1—Support for up to nine EX4500 switches

Mixed EX4200 and EX4550 Virtual Chassis

12.2R1—Initial release. Support for up to ten total EX4200 and EX4550 switches

Mixed EX4200, EX4500, and EX4550 Virtual Chassis

12.2R1—Initial release. Support for up to ten total EX4200, EX4500, and EX4550 switches

Mixed EX4300 and EX4600 Virtual Chassis

13.2X51-D25—Initial release. Support for up to ten total EX4300 and EX4600 switches. EX4600 switches 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. Support for up to ten total EX4500 and EX4550 switches

EX9200 Virtual Chassis

13.2R2—Initial release. Support for up to two EX9200 switches.

Note: Support forEX9200 switches in a Virtual Chassis was phased out 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.

Maximum Switch Support in a QFX Series Virtual Chassis (Including Mixed Virtual Chassis with EX Series Switches)

In a QFX5200 Virtual Chassis, you can interconnect up to a maximum of 3 standalone QFX5200 switches as a non-mixed Virtual Chassis. (QFX5200 switches cannot be mixed with other types of switches in a Virtual Chassis.)

For all other QFX Series Virtual Chassis, you can interconnect up to 10 standalone switches in the following supported combinations:

  • QFX5110 switches or a combination of QFX5110 switches and QFX5100 switches (a non-mixed Virtual Chassis)

  • QFX5100 switches (a non-mixed Virtual Chassis)

  • QFX5100 switches with any combination of QFX3500 and QFX3600 switches, and EX4300 switches excluding the multigigabit models (a mixed mode Virtual Chassis)

  • QFX3500 switches, or QFX3600 swtiches, or any combination of QFX3500 switches and QFX3600 switches (a non-mixed Virtual Chassis)

  • Any combination of QFX3500 and QFX3600 switches with EX4300 switches excluding the multigigabit models (a mixed mode Virtual Chassis)

Note

In Junos OS release 13.2X51-D20, you can interconnect only up to four QFX5100-96S switches in a non-mixed QFX5100 Virtual Chassis. Starting in Junos OS release 13.2X51-D25, you can configure up to ten QFX5100-96S switches into a mixed or non-mixed QFX5100 Virtual Chassis.

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; these ports can only be used as VCPs and cannot be reconfigured as network ports. Dedicated VCPs allow you to interconnect switches without requiring any additional interface configuration.

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

Most switches have optical or uplink ports that can also be configured as 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, you must configure the VCPs. Also, 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 2 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 what transceivers and cables are supported to use for VCP connections on the switch, see the hardware documentation for that type of switch.

Table 2: 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

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 (0 through 3)

EX3400

None

All QSFP+ uplink ports

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

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+ 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

QFX3500 and QFX3600

None

None

Any non-channelized 40-Gbps QSFP+ interfaces

QFX5100

None

None

Any non-channelized 40-Gbps QSFP+ interfaces

QFX5110

None

None

Any 100-Gbps or 40-Gbps QSFP28 ports

Any non-channelized 40-Gbps QSFP+ interfaces

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

QFX5200

None

None

Any 40-Gbps QSFP+ ports

In Junos OS Release 17.3R2-S4, 100-Gbps QSFP28 ports are also supported 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 referred to as autoprovisioning the new member.

Ports that are configured as VCPs by default on a switch or that were previously configured into VCPs must be converted back into network ports using the request virtual-chassis vc-port delete command for the port to be eligible for automatic VCP conversion. A port that has been automatically converted into a VCP is not automatically converted back into a network port when you remove a switch from a Virtual Chassis and disconnect the link.

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 occur even if the ports are manually converted into VCPs to create the redundant VCP link with a dedicated VCP link, so the reboot is required to avoid traffic looping in that case as well.)

  • Starting in Junos OS Releases 14.1X53-D47, 17.4R2, 18.1R3, 18.2R2, and 18.3R1 for EX4300, EX4600, and QFX Series Virtual Chassis (which have the automatic VCP conversion feature enabled by default), you can choose to disable the feature by configuring the no-auto-conversion statement 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 interfaces between the same two switches into VCPs. When multiple VCPs interconnect the same two member switches, a Link Aggregation Group (LAG) or bundle is automatically formed when the VCPs are on interfaces supporting identical speeds. For example, if you have two 40-Gbps QSFP+ interfaces configured as VCPs between member switches, a LAG with two member links with 80-Gbps of total bandwidth is formed. However, 10-Gigabit SFP+ and 40-Gbps QSFP+ interfaces configured as VCPs 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 forwarded by the Virtual Chassis. 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 is assigned one of two roles: Routing Engine role or linecard role, and for Routing Engine role, receives a further designation as the master or backup Routing Engine.

The member that functions as the master in the Routing Engine role 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, 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.

All switches that are not assigned the master or backup Routing Engine role function 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, any switch can be configured in any role in any configuration.

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

  • In a mixed EX4600 Virtual Chassis with EX4300 switches, an EX4600 switch must assume the master 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. If the mixed Virtual Chassis does not contain QFX5100 switches, we recommend configuring QFX3500 or QFX3600 switches into the Routing Engine role.

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

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.

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

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, any switch can be configured in any role in any configuration.

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

  • In a mixed EX4600 Virtual Chassis with EX4300 switches, we strongly recommend configuring an EX4600 switch into the backup role. A mixed EX4600 and EX4300 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 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. If the mixed Virtual Chassis does not contain QFX5100 switches, we recommend configuring QFX3500 or QFX3600 switches into the Routing Engine role.

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

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 makes it ineligible for functioning as a master or backup Routing Engine.

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.

Any switch can function in the linecard role in a mixed or non-mixed Virtual Chassis.

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. If the mixed Virtual Chassis 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 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 or backup Routing Engine role, or linecard role) 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 Routing Engine role.

The default value for mastership priority is 128. 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.

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 is shut 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 a member switch is taken 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 18.4R1, up to four 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 ten 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.
In Junos OS Release 17.3R2-S4, 100-Gbps QSFP28 ports are also supported 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, and QFX Series Virtual Chassis (which have the automatic VCP conversion feature enabled by default), you can choose to disable the feature by configuring the no-auto-conversion statement at the [edit virtual-chassis] hierarchy level on the Virtual Chassis.
Starting in Junos OS release 13.2X51-D25, you can configure up to ten QFX5100-96S switches into a mixed or non-mixed QFX5100 Virtual Chassis.
In Junos OS release 13.2X51-D20, you can interconnect only up to four QFX5100-96S switches in a non-mixed QFX5100 Virtual Chassis.
Starting in Junos OS Release 13.2X50-D20, EX4300 switch support was added in a mixed QFX Series Virtual Chassis or in a VCF.
Starting in Junos OS Release 12.2R1, an EX3300 Virtual Chassis can support up to ten EX3300 member switches.