As part of SSR software upgrade procedure in https://www.juniper.net/documentation/us/en/software/session-smart-router/docs/intro_upgrading/#upgrading-a-router , Download of software packages fails

Below lines can be noticed in the logs

salt-minion[7379]: [FAILED] kernel-core-4.18.0-513.9.1.el8_9.x86_64.rpm: No more mirrors to try - All mirrors were already tried without success

salt-minion[7379]: Error: Error downloading packages:

salt-minion[7379]: Cannot download 128tech/kernel-core-4.18.0-513.9.1.el8_9.x86_64.rpm: All mirrors were tried

salt-minion[7379]: Exiting with exception: DownloadError

salt-minion[7379]: Failed to download one of the following packages: ('128T-manifest-0:6.1.5.14.lts.el7-1.x86_64', '128T-deprecated-packages-0:6.1.5.14.lts.el7-1.x86_64', 'shim-x64', 'grub2-efi-x64')

Whenever an upgrade fails or get stuck in between, we need to inspect the logs for the reason of failure. 

One of the below command can be run to check the logs

# tail -n100 /var/log/128tinstaller/installer.log
or 
# less /var/log/128tinstaller/installer.log

Make sure basic connectivity to 128T repositories are fine. For issues in download packages from software repositories over yum/dnf command, these steps can be performed to clean and refresh the dnf / yum metadata cache.

# dnf clean all

# dnf makecache

On successful execution of previous command, retry upgrade again.