Fix call function of mobile Facebook Messenger

Tested environment
1. Android 9 Oneplus6
2. iOS 12 Iphone SE

This issue has been annoyed me for couple months. While using VPN (Self-hosted) with IPv6 ready, then call function on Facebook Messenger will disappeared. While using VPN.ac (Singapore, Hongkong, Japan) will affected. Also VPS provider such as Vultr.com, Digitalocean.com, Linode.com (Singapore and Japan, Los Angeles) have this issue too… I gonna create 10x VPS at once, try all IPv4 manually, and delete those useless vps node 😭

VPN stacks:
1. OpenVPN (IPv4, IPv6 — TCP, UDP both OK)
2. iKEv2 (only IPv4, OK, with IPv6 not work)
3. Wireguard (only IPv4, OK, with IPv6 not work)
4. Openconnect (only IPv4, OK, with IPv6 not work)

Example screenshot

Solution 1: Disable eth0 IPv6

// nano /etc/sysctl.conf

# to disable IPv6 on all interfaces system wide
net.ipv6.conf.all.disable_ipv6 = 1

# to disable IPv6 on a specific interface (e.g., eth0, lo)
net.ipv6.conf.lo.disable_ipv6 = 1
net.ipv6.conf.eth0.disable_ipv6 = 1

// restart it
sysctl -p

Solution 2: Disable IPv6 on VPN software

Reference :http://ask.xmodulo.com/disable-ipv6-linux.html

Photo by 🇨🇭 Claudio Schwarz | @purzlbaum on Unsplash