[DISCUSSION] Is it possible to add an option for using IPv6 only?

[roland-reed]

These days I have encounter a problem which is related to IPv4 & IPv6, here is the problem:

• Commands like npm publish or npm view will fail with error connection timeout (connecting to IP of IPv4 of registry.npmjs.org) after default timeout (5 mins)
• DNS resolving works normally, returns IPv4 IPs and IPv6 IPs
• ping <IPv4 IP> works
• curl -4 https://registry.npmjs.org always timed out
• curl -6 https://registry.npmjs.org works

I understand that this is a network issue, not a bug, but I wonder if there is a possibility to add an option like ipv6Only to make npm-registry-fetch and npm only use IPv6 in certain conditions.

If it sounds reasonable, I can make a PR.

Thanks.

Related: [npm-registry-fetch issue](https://github.com/npm/npm-registry-fetch/issues/226)