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If you edited your /etc/apt/sources.list this is the default. Some sources can also be under /etc/apt/sources.list.d/
Sources.list example:
deb http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware deb-src http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware
deb http://deb.debian.org/debian-security/ bookworm-security main contrib non-free non-free-firmware deb-src http://deb.debian.org/debian-security/ bookworm-security main contrib non-free non-free-firmware
deb http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware deb-src http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware
If you want to also download from another mirror at the exact same time so you get concurrent downloads, you can add a mirror (security mirrors usually dont work for testing) but on a stable release it would be like this:
#Mirror deb http://ftp.us.debian.org/debian bookworm main contrib non-free non-free-firmware deb http://ftp.us.debian.org/debian-security/ bookworm-security main contrib non-free non-free-firmware deb http://ftp.us.debian.org/debian bookworm-updates main contrib non-free non-free-firmware
A complete file would be like this :
# This system was installed using small removable media # (e.g. netinst, live or single CD). The matching "deb cdrom" # entries were disabled at the end of the installation process. # For information about how to configure apt package sources, # see the sources.list(5) manual. # deb http://deb.debian.org/debian/ bookworm-backports main contrib non-free deb http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware deb-src http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware deb http://deb.debian.org/debian-security/ bookworm-security main contrib non-free non-free-firmware deb-src http://deb.debian.org/debian-security/ bookworm-security main contrib non-free non-free-firmware deb http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware deb-src http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware #Mirror deb http://ftp.us.debian.org/debian bookworm main contrib non-free non-free-firmware deb http://ftp.us.debian.org/debian-security/ bookworm-security main contrib non-free non-free-firmware deb http://ftp.us.debian.org/debian bookworm-updates main contrib non-free non-free-firmware
