force apt (apt-get) to use ipv4

[Bonno Bloksma <b.bloksma@tio.nl>]

Hi,

I know I have a problem with ipv6 on one machine where ipv6 is enabled but cannot reach outside the local network and ipv4 has a proper working network connection to the outside world.

Trying to get apt (or apt-get) to update results in :
Ign:1 http://ftp.nl.debian.org/debian stretch InRelease
Ign:2 http://ftp.nl.debian.org/debian stretch-updates InRelease
Err:3 http://ftp.nl.debian.org/debian stretch Release
  Cannot initiate the connection to ftp.nl.debian.org:80 (2001:67c:2564:a120::21). - connect (101: Network is unreachable) [IP: 2001:67c:2564:a120::21 80]
Err:4 http://ftp.nl.debian.org/debian stretch-updates Release
  Cannot initiate the connection to ftp.nl.debian.org:80 (2001:67c:2564:a120::21). - connect (101: Network is unreachable) [IP: 2001:67c:2564:a120::21 80]
[...]
Etc.

How can I force apt and apt-get to use IPv4 to update my Debian softwarem of this machine?

Bonno Bloksma