About using IPv6 with file_get_contents in PHP (switching IP when going outside)

I rent Conoha's VPS (CentOS 6.5).
PHP is 5.6.

Conoha has 17 IPv6s if you select standard os (CentOS 6.5).
Adding IPv4 is a fee, so I would like to make the most of IPv6 as much as possible.

I tried the following code in the PHP documentation because file_get_contents can use context.

<?php
$opts=array(
　　　　'socket' = > array(
　　　　　　　　'bindto' = > '[IPv6 in my environment]: Any port',
　　　　),
);

$context=stream_context_create($opts);
echo file_get_contents('http://www.example.com', false,$context);

?>

Even if you specify a context as described above,

• file_get_contents():Invalid IP Address: IPv6 in your environment

The error appears.

The following is the situation.

• All 17 of the IPv6s in question can be reversed, and I think the configuration is correct.
• I tried all 17 IPv6s, but I got an error (both abbreviated and full).
• Context specification (IP switching) is successful for IPv4 added separately.
• The site you are connecting to is IPv6-capable.

How can I get out of PHP via IPv6?
If you can switch between IP (IPv6) and retrieve data, I don't care about file_get_contents.

I look forward to your kind cooperation.

Additional information about the matter you confirmed in the comment

• 1.ping6 is successful.(Successful on sites such as ipv6.google.com)

• 2.ip6 tables has the following settings:

  —INPUT ACCEPT [0:0]
  —FORWARD ACCEPT [0:0]
  —OUTPUT ACCEPT [0:0]
  -AINPUT-m state --state ESTABLISHED, RELATED-j ACCEPT
  -AINPUT-pipv6-icmp-j ACCEPT-AINPUT-ilo-j ACCEPT
  -AINPUT-m state --state NEW-mudp-pudp --dport546-d [band of IPv6 in your environment] -j ACCEPT
  -AINPUT-m state --state NEW-m tcp-p tcp --dport22-j ACCEPT
  -AINPUT-j REJECT -- reject-with icmp6-adm-prohibited
  -A FORWARD-j REJECT -- reject-with icmp6-adm-prohibited
  COMMIT

• Disabling 3.ip6 tables did not change the error that appeared.
  　

• 4.php-i | grep-ipv6 has the following results:

  $php-i | grep-ipv6
  IPv6 Support=>enabled
  IPv6 = > Yes

• 5. Try 'bindto'=>'[0]:0' (leave it to os).

2. The ip6 tables settings are as follows:

—INPUT ACCEPT [0:0]
—FORWARD ACCEPT [0:0]
—OUTPUT ACCEPT [0:0]
-AINPUT-m state --state ESTABLISHED, RELATED-j ACCEPT
-AINPUT-pipv6-icmp-j ACCEPT-AINPUT-ilo-j ACCEPT
-AINPUT-m state --state NEW-mudp-pudp --dport546-d [band of IPv6 in your environment] -j ACCEPT
-AINPUT-m state --state NEW-m tcp-p tcp --dport22-j ACCEPT
-AINPUT-j REJECT -- reject-with icmp6-adm-prohibited
-A FORWARD-j REJECT -- reject-with icmp6-adm-prohibited
COMMIT

3. Disabling ip6 tables did not change the error that appeared.
　

4. The results of the php-i | grep-ipv6 attempt are as follows:

$php-i | grep-ipv6
IPv6 Support=>enabled
IPv6 = > Yes

5. Try 'bindto'=>'[0]:0' for the bindto part of the PHP program.

No errors occur, but when you try to connect to a server that you own separately, you can get the default IPv4 awarded when you rent a VPS tied to interface eth0:

<?php
    echo$_SERVER ["REMOTE_ADDR" ];

• 6. 'bindto'=>'[::1]:0' has the following results:

The following error occurred:

file_get_contents():Invalid IP Address:::1

The default IPv4 IP was obtained in the script for another server used in 5. above.

• 7. Make sure the IP address is properly formatted (with or without full-width characters, abbreviated errors)

I checked again, but there were no inappropriate characters such as full-width characters.
There is no description of whether :: is : because there is no contiguous area in your IPv6 at 0000.
"Also, there are several parts of the IPv6 that can omit ""0"" such as ""0090"", so I checked again to see if there are any mistakes in the omission."I also tried again with a full notation that does not omit zero, but the error still appears.

• A temporary solution?

In conclusion, I found that IPv6 context switching is possible in the file_get_contents directly specified by IPv6 that you suggested in the comment.

If IPv6 is directly specified, no errors are received and the source IP is IPv6.I have a question about why I get an error when I specify a domain, but I would like to solve it once because the method you suggested will satisfy my purpose.

Thank you for all your advice.