Surely you are thinking: “IPv4 is ‘dead’, it does not make sense to force IPv4”, in an ideal world, you would be right .
But the reality is that a large part of the infrastructure of the network is not ready for IPv6.
My experience with apt-get on stable Debian in the UK has been painful.
Most of the “gateways” I have to manage in my work suffer from terribly slow connections when try-get tries to update repositories or download packages.
So we have had to configure such systems for queapt-get to make IPv4 connections instead of IPv6.
To tell apt-get to limit its connections to IPv4, the following parameter is used:
apt-get -o Acquire::ForceIPv4=true update
apt-get -o Acquire::ForceIPv6=true update
To make apt-get connect always via IPv4, we created the file 99force-ipv4 in /etc/apt/apt.conf.d/.
$ nano /etc/apt/apt.conf.d/99force-ipv4
And we write the following content:
Save the file and from that moment all connections will be made through IPv4.
If instead of a 4 you put a 6, you will limit the connections only to IPv6.
The best way to know which one to choose is to simply try and see which one works best for you.