Regular expression that matches valid IPv6 addresses

Answer 1

Regexes for ipv6 can get really tricky when you consider addresses with embedded ipv4 and addresses that are compressed, as you can see from some of these answers.

The open-source IPAddress Java library will validate all standard representations of IPv6 and IPv4 and also supports prefix-length (and validation of such). Disclaimer: I am the project manager of that library.

Code example:

        try {
            IPAddressString str = new IPAddressString("::1");
            IPAddress addr = str.toAddress();
            if(addr.isIPv6() || addr.isIPv6Convertible()) {
                IPv6Address ipv6Addr = addr.toIPv6();
            }
            //use address
        } catch(AddressStringException e) {
            //e.getMessage has validation error
        }

Answer 2

Beware! In Java, the use of InetAddress and related classes (Inet4Address, Inet6Address, URL) may involve network trafic! E.g. DNS resolving (URL.equals, InetAddress from string!). This call may take long and is blocking!

For IPv6 I have something like this. This of course does not handle the very subtle details of IPv6 like that zone indices are allowed only on some classes of IPv6 addresses. And this regex is not written for group capturing, it is only a "matches" kind of regexp.

S - IPv6 segment = [0-9a-f]{1,4}

I - IPv4 = (?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9]{1,2})\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9]{1,2})

Schematic (first part matches IPv6 addresses with IPv4 suffix, second part matches IPv6 addresses, last patrt the zone index):

(
(
::(S:){0,5}|
S::(S:){0,4}|
(S:){2}:(S:){0,3}|
(S:){3}:(S:){0,2}|
(S:){4}:(S:)?|
(S:){5}:|
(S:){6}
)
I

|

:(:|(:S){1,7})|
S:(:|(:S){1,6})|
(S:){2}(:|(:S){1,5})|
(S:){3}(:|(:S){1,4})|
(S:){4}(:|(:S){1,3})|
(S:){5}(:|(:S){1,2})|
(S:){6}(:|(:S))|
(S:){7}:|
(S:){7}S
)

(?:%[0-9a-z]+)?

And here the might regex (case insensitive, surround with what ever needed like beginning/end of line, etc.):

(?:
(?:
::(?:[0-9a-f]{1,4}:){0,5}|
[0-9a-f]{1,4}::(?:[0-9a-f]{1,4}:){0,4}|
(?:[0-9a-f]{1,4}:){2}:(?:[0-9a-f]{1,4}:){0,3}|
(?:[0-9a-f]{1,4}:){3}:(?:[0-9a-f]{1,4}:){0,2}|
(?:[0-9a-f]{1,4}:){4}:(?:[0-9a-f]{1,4}:)?|
(?:[0-9a-f]{1,4}:){5}:|
(?:[0-9a-f]{1,4}:){6}
)
(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9]{1,2})\.){3}
(?:25[0-5]|2[0-4][0-9]|[01]?[0-9]{1,2})|

:(?::|(?::[0-9a-f]{1,4}){1,7})|
[0-9a-f]{1,4}:(?::|(?::[0-9a-f]{1,4}){1,6})|
(?:[0-9a-f]{1,4}:){2}(?::|(?::[0-9a-f]{1,4}){1,5})|
(?:[0-9a-f]{1,4}:){3}(?::|(?::[0-9a-f]{1,4}){1,4})|
(?:[0-9a-f]{1,4}:){4}(?::|(?::[0-9a-f]{1,4}){1,3})|
(?:[0-9a-f]{1,4}:){5}(?::|(?::[0-9a-f]{1,4}){1,2})|
(?:[0-9a-f]{1,4}:){6}(?::|(?::[0-9a-f]{1,4}))|
(?:[0-9a-f]{1,4}:){7}:|
(?:[0-9a-f]{1,4}:){7}[0-9a-f]{1,4}
)

(?:%[0-9a-z]+)?

Answer 3

This catches the loopback(::1) as well and ipv6 addresses. changed {} to + and put : inside the first square bracket.

([a-f0-9:]+:+)+[a-f0-9]+

tested on with ifconfig -a output http://regexr.com/

Unix or Mac OSx terminal o option returns only the matching output(ipv6) including ::1

ifconfig -a | egrep -o '([a-f0-9:]+:+)+[a-f0-9]+'

Get All IP addresses (IPv4 OR IPv6) and print match on unix OSx term

ifconfig -a | egrep -o '([0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}) | (([a-f0-9:]+:+)+[a-f0-9]+)'

Answer 4

InetAddressUtils has all the patterns defined. I ended-up using their pattern directly, and am pasting it here for reference:

private static final String IPV4_BASIC_PATTERN_STRING =
        "(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\\.){3}" + // initial 3 fields, 0-255 followed by .
         "([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])"; // final field, 0-255

private static final Pattern IPV4_PATTERN =
    Pattern.compile("^" + IPV4_BASIC_PATTERN_STRING + "$");

private static final Pattern IPV4_MAPPED_IPV6_PATTERN = // TODO does not allow for redundant leading zeros
        Pattern.compile("^::[fF]{4}:" + IPV4_BASIC_PATTERN_STRING + "$");

private static final Pattern IPV6_STD_PATTERN =
    Pattern.compile(
            "^[0-9a-fA-F]{1,4}(:[0-9a-fA-F]{1,4}){7}$");

private static final Pattern IPV6_HEX_COMPRESSED_PATTERN =
    Pattern.compile(
            "^(([0-9A-Fa-f]{1,4}(:[0-9A-Fa-f]{1,4}){0,5})?)" + // 0-6 hex fields
             "::" +
             "(([0-9A-Fa-f]{1,4}(:[0-9A-Fa-f]{1,4}){0,5})?)$"); // 0-6 hex fields 

Answer 5

Depending on your needs, an approximation like:

[0-9a-f:]+

may be enough (as with simple log file grepping, for example.)

Answer 6

Here's what I came up with, using a bit of lookahead and named groups. This is of course just IPv6, but it shouldn't interfere with additional patterns if you want to add IPv4:

(?=([0-9a-f]+(:[0-9a-f])*)?(?P<wild>::)(?!([0-9a-f]+:)*:))(::)?([0-9a-f]{1,4}:{1,2}){0,6}(?(wild)[0-9a-f]{0,4}|[0-9a-f]{1,4}:[0-9a-f]{1,4})