For DN42-only clients I host an instance of apt-cacher-ng at mirror.uffsalot.dn42:3142.

There are 2 ways to use this mirror.

1. Configure it as a proxy in your apt.conf

   Acquire::http { Proxy "http://mirror.uffsalot.dn42:3142"; };
   Beware! You MUST choose a origin mirror which is dualstack or IPv6 only, as the container only has a public IPv6 address.

2. Replace your source.list entries with my hostname

   deb http://mirror.uffsalot.dn42/debian/ unstable main
   Only works for Debian & Ubuntu. Maybe I will sometime create a full mirror at this address, but for now this is only a reverse proxy for apt-cacher-ng.