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Changes in Behavior and Syntax


This section lists the changes in behavior of Junos OS features and changes in the syntax of Junos OS statements and commands from Junos OS Release 15.1R7 for the EX Series.

Dynamic Host Configuration Protocol

  • Format change for DHCP Option 18—On EX9200 switches with DHCP snooping configured, when the VLAN ID is appended to the prefix of DHCP option 18, it appears in decimal format instead of hexadecimal format.

High Availability (HA) and Resiliency

  • VRRP session flap configuring fast-interval (EX9200 switch)—Starting in Junos OS Release 15.1R7, we recommend that you set the fast-interval value to a minimum of 500 milliseconds. A VRRP session can flap if a value less than 500 is configured and committed.

    [See fast-interval.]


  • Support for status deprecated statement in YANG modules (EX Series)—Starting with Junos OS Release 15.1R5, Juniper Networks YANG modules includethe status deprecated statement to indicateconfiguration statements, commands, and options that are deprecated.

Virtual Chassis

  • Increased time to rejoin Virtual Chassis after a member is rebooted (EX2200, EX3300, EX4200, and EX8200 Virtual Chassis)—Starting in Junos OS Release 15.1R3, when one or more member switches in an EX2200, EX3300, EX4200, or EX8200 Virtual Chassis are rebooted, the Virtual Chassis master’s delay time before reinstating the rebooted switch as a member in the Virtual Chassis is increased from two minutes to ten minutes. As a result, after rebooting a Virtual Chassis member, up to 15 or 20 minutes total elapsed time might be required for the member to completely rejoin the Virtual Chassis. The increased delay time allows the Virtual Chassis to correctly rebuild its Virtual Chassis port (VCP) adjacency information, and avoids unexpected mastership election contention or failure of the Virtual Chassis to re-form.

  • Automatic software update (EX2200 Virtual Chassis)—Starting in Junos OS Release 15.1R7, the automatic software update feature can be used to automatically update Junos software on members of an EX2200 Virtual Chassis running Junos OS Release 12.3R12 and later. Automatic software update is not supported on an EX2200 Virtual Chassis in releases prior to 15.1R7.

    [See Understanding Automatic Software Update on Virtual Chassis Member Switches.]

  • Automatic Virtual Chassis port conversion disabled by default (EX2200, EX3300, EX4200, EX4500, and EX4550 Virtual Chassis)—Starting in Junos OS Release 15.1R7, automatic Virtual Chassis port (VCP) conversion is disabled by default in an EX2200, EX3300, EX4200, EX4500, and EX4550 Virtual Chassis. Previously, automatic VCP conversion was always enabled by default on these switches in a Virtual Chassis.

    When automatic VCP conversion is enabled, if you add a new member to a Virtual Chassis or add a new link between two existing members in a Virtual Chassis, the ports on both sides of the link are automatically converted into VCPs when all of the following conditions are true:

    • LLDP is enabled on the interfaces for the members on both sides of the 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 ports on both ends of the link are supported as VCPs and are not already configured as VCPs.

    Automatic VCP conversion is not needed when using dedicated VCPs or default-configured VCPs on both sides of the link to interconnect two members. You can also manually configure network or uplink ports that are supported as VCPs on both ends of the link, instead of using the automatic VCP conversion feature.


    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, you must reboot the Virtual Chassis to avoid creating a traffic loop within the Virtual Chassis. This step is also required if the ports for the redundant link are manually configured into VCPs.

    To enable automatic VCP conversion in an EX2200, EX3300, EX4200, EX4500, and EX4550 Virtual Chassis, configure the auto-conversion statement at the [edit virtual-chassis] hierarchy level on the Virtual Chassis. Subsequently deleting the auto-conversion statement returns the Virtual Chassis to the default behavior, in which automatic VCP conversion is disabled.