This article provides information about Junos version supportability for VC with a mix of QFX5100 and QFX5110.

QFX5110 Virtual Chassis with QFX5100 switches can only be set up using QFX5110 and QFX5100 switches running the same Junos OS image that includes “-qfx-5e-” in the Junos OS software package filename downloaded from the Software Center. 

QFX5100 switches running a Junos OS image filename that includes “-qfx-5-” must first be upgraded to the “-qfx-5e-” image to join a QFX5110 Virtual Chassis. 

For more details check Understanding QFX5100 and QFX5110 Switches in a Virtual Chassis.

As per End of Life Announcement: QFX5100, Junos 21.4 is Last Software Version (LSV) for QFX5100.

Junos image support on QFX5100 is up to 21.4R3-Sx, it includes all scenarios of it's deployment i.e. standalone, homogenous VC (QFX5100 VC) or mixed VC (QFX5100+QFX5110).

Understanding QFX5100 and QFX5110 Switches in a Virtual Chassis

End of Life Announcement: QFX5100