I need to update/upgrade Raspbian on some Pis behind a firewall and I need to tell the network admin which servers and mirror will be used for that purpose.
I see that the mirror is not always the same, which causes trouble.
How should I modify the apt source.list file to use a single dedicated mirror (say http://ftp.igh.cnrs.fr) in addition (if still needed) to http://raspbian.raspberrypi.org and https://archive.raspberrypi.org, but no other?
My current apt source.list file contains:
deb http://raspbian.raspberrypi.org/raspbian/ buster main contrib non-free rpi
deb https://archive.raspberrypi.org/debian/ buster main ui
Thanks in advance for the answer