APT_USE_IPV4
Set this environment variable to force network class to use only IPv4 protocols.
The default is to use the IPv6/IPv4 dual stack protocol.
Set
the APT_USE_IPV4 environment variable in the following circumstances:
- If your computer is only IPv4 enabled and IPv6 protocol is disabled.
- If your computer has IPv4 address mapping defined in /etc/hosts file.