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Understanding Virtual Chassis Port Link Aggregation


This topic applies to all EX Series and QFX Series Virtual Chassis, except for EX8200 Virtual Chassis. See Understanding Virtual Chassis Port Link Aggregation in an EX8200 Virtual Chassis for information about EX8200 Virtual Chassis link aggregation.

Within a Virtual Chassis, you can combine physical Ethernet ports to form a logical point-to-point link known as a link aggregation group (LAG) or bundle. The interfaces that are included in a LAG are sometimes referred to as member interfaces. Do not confuse this term with member switches, which refers to switches that are interconnected into a Virtual Chassis. A LAG in a Virtual Chassis can be composed of member interfaces located in different member switches in the Virtual Chassis, or composed of multiple redundant Virtual Chassis Port (VCP) links between two member switches in the Virtual Chassis, as described in the following sections.

Virtual Chassis Network Interface LAG Among Virtual Chassis Members

When setting up interfaces in a Virtual Chassis, you can configure a combination of physical Ethernet ports belonging to different member switches to form a LAG. A LAG provides more bandwidth than a single Ethernet link can provide. Additionally, link aggregation provides network redundancy by load-balancing traffic across all available links. If one of the links fails, the system automatically load-balances traffic across all remaining links.

Similarly, if a Virtual Chassis member switch that has LAG member interfaces on multiple member switches fails for any reason, the traffic traversing the LAG can be redirected through the active member switch. This setup has benefits for failover purposes and can be especially beneficial in cases when a member switch needs to be inactive for some time, such as during a software upgrade using NSSU.


During an NSSU operation, if you try to view LAG interface status on the master Routing Engine member using the show interfaces ae-ae-interface-number CLI command, you might see incorrect or zero traffic counts. To work around this problem, run the command on the backup Routing Engine member instead if that member is already loaded and running.

Virtual Chassis Port LAG Between Two Virtual Chassis Members

You can configure optical uplink ports into Virtual Chassis ports (VCPs) that connect EX Series or QFX series switches together to form a Virtual Chassis. When you configure multiple uplink port VCPs connecting the same two member switches, those ports automatically form a LAG if the ports are configured to operate at the same link speeds. Each LAG is assigned a positive-integer identifier called a trunk ID. Up to 8 redundant VCP links can form a VCP LAG connecting two members in a Virtual Chassis, depending on the number of available ports that can be VCPs.


On EX2200 and EX2200-C switches, you can also configure the RJ-45 interfaces, including built-in network ports with 10/100/1000BASE-T Gigabit Ethernet connectors and 1000BASE-T RJ-45 transceivers, into VCPs. Any interfaces on these switches that are configured as VCPs interconnecting two members will automatically form a LAG, regardless of whether the interfaces are optical transceiver interfaces, RJ-45 transceiver interfaces, or built-in network ports with 10/100/1000BASE-T Gigabit Ethernet connectors.

A VCP LAG automatically forms when any two member switches are interconnected with two or more VCP links of the same link speed in any of these configurations:

  • If the VCP ports on both switches are ports you configured into VCPs or default-configured VCPs (for switches that have default VCPs).

  • If the VCP ports on both switches are dedicated VCPs (for switches that have dedicated VCPs).

  • In a mixed Virtual Chassis when the VCP links interconnect two different switch models.

A LAG over uplink VCPs provides higher overall bandwidth for forwarding traffic between the member switches connected by the optical VCPs, faster management communications, and greater redundancy of operations among the members than would be available without the LAG.

See Setting an Uplink Port on an EX Series or QFX Series Switch as a Virtual Chassis Port or Configuring an EX4650 or a QFX Series Virtual Chassis for information about configuring uplink ports into VCPs.