This article outlines an issue where after a software upgrade in a 2 member QFX5100 VC the inband became inaccessible.

The inband access is through network port with uplink interface having 2 links in the ae bundle.

QFX5100[VC]-------ae1--------------MX [Uplink device]

After the upgrade the inband is inaccessible.

One of the links in the ae bundle shows up on QFX5100 side but ae bundle is still down.

This problem is due to mis-configuration of minimum link configuration where the minimum link is set to 1 on QFX side while minimum link in the same ae bundle is configured as 2 on MX side. So the ae bundle will not be up.

So the standard for the minimum link configuration in an ae bundle should be uniform on both the end devices.

More details on minimum link configuration in below link.

https://www.juniper.net/documentation/us/en/software/junos/interfaces-security-devices/topics/ref/statement/interfaces-edit-minimum-links.html