Create a sysctl config file:
```bash
tee /etc/sysctl.d/99-disable-ipv6.conf >/dev/null <<'EOF'
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
EOF
```

Apply the settings:
```bash
sudo sysctl --system
```

Verify:
```bash
cat /proc/sys/net/ipv6/conf/all/disable_ipv6
```