Offline APT Repo

apt update

# recursive apt dependencies
apt install apt-rdepends

# this downloads all deb packages of dnsmasq and dependencies. Filter out debconf-2.0 because dependency is missing
apt download $(apt-rdepends dnsmasq|grep -v "^ "|grep --invert-match debconf-2.0)

https://stackoverflow.com/a/27469489/9397749

apt install dpkg-dev

dpkg-scanpackages . /dev/null | gzip -9c > Packages.gz

apt install genisoimage

genisoimage -J -o apt-local.iso ./pkg

¹⁾

-J generates case sensitive filenames, which apt needs²⁾

rename debian.sources. add this to sources.list

/etc/apt/sources.list

deb [trusted=yes] file:/mnt/cdrom ./

https://askubuntu.com/a/458754/1977823

More from ubuntu documentation: https://help.ubuntu.com/community/Repositories/Personal