curl port 443: Network is unreachable problem

curl-problem.md

How to solve the curl port 443: Network is unreachable problem:

joridos@localhost:~/Documents/github$ opam init
default    Downloading https://opam.ocaml.org/urls.txt
'opam init' failed.
# opam-version    1.1.1
# os              linux
Cannot download https://opam.ocaml.org/urls.txt, please check your connection settings.
joridos@localhost:~/Documents/github$ curl https://opam.ocaml.org/urls.txt
curl: (7) Failed to connect to opam.ocaml.org port 443: Network is unreachable

just do it:

echo ipv4 >> ~/.curlrc