Here is a working snippet of a preseed.cfg which works with apt-cacher-ng out of the box:
# Mirror settings # If you select ftp, the mirror/country string does not need to be set. #d-i mirror/protocol string ftp #d-i mirror/country string GB d-i mirror/country string manual d-i mirror/http/hostname string ftp.uk.debian.org d-i mirror/http/directory string /debian d-i mirror/http/proxy string http://192.168.1.23:3142/
You will need to change the IP of the apt-cacher-ng server to the correct IP/hostname - 192.168.1.23 in the above example.
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