This article discusses a scenario in which the two routing-engines of a Juniper MX device are on different Junos versions. When the user tried to upgrade the older Junos version to match the new Junos Version, an error was observed.

In this scenario, RE0 was the primary while RE1 was the back-up. They were on Junos versions with different bit systems. RE0 was on a 64 bit version while RE1 was on a 32 bit version.

RE1 was to be upgraded from it's 32 bit version to the 64 bit version. The 'request vmhost software add..' command was executed from RE0, the current primary. However, the upgrade command returned an authentication error:

request vmhost software add no-validate /var/tmp/junos-vmhost-install-mx-x86-64-16.1R6-S3.1.tgz re1 reboot
mgd: unable to execute /opt/support/vmhost-pkg-support: Authentication error
warning: Host software installation has failed.

The difference in the Junos versions between the REs can lead to communication issues between them.

Run the command,  'request vmhost software add..' directly from RE1, the routing-engine which is to be upgraded. This avoided errors and the upgrade was successful. Both routing-engines were eventually on the same 64 bit Junos version.