A few notes about IPv6 "IPv4 mapped" addresses and their observed use in Java. "IPv4 mapped" addresses were originally a representation of IPv4 addresses for use on an IPv6 socket that could receive both IPv4 and IPv6 connections (by disabling the IPV6_V6ONLY socket option on an IPv6 socket). Yes, it's confusing. Nevertheless, these "mapped" addresses were never supposed to be seen on the wire. That assumption was dropped, some say mistakenly, in later RFCs with the apparent aim of making IPv4-to-IPv6 transition simpler.

Technically one can create a 128bit IPv6 address with the wire format of a "mapped" address, as shown above, and transmit it in an IPv6 packet header. However, Java's InetAddress creation methods appear to adhere doggedly to the original intent of the "mapped" address: all "mapped" addresses return Inet4Address objects.

For added safety, it is common for IPv6 network operators to filter all packets where either the source or destination address appears to be a "compat" or "mapped" address. Filtering suggestions usually recommend discarding any packets with source or destination addresses in the invalid range ::/3 , which includes both of these bizarre address formats. For more information on "bogons", including lists of IPv6 bogon space, see:

Since:

Author:

Erik Kline

forString

public static InetAddress forString(String ipString)

Parameters:

ipString - String containing an IPv4 or IPv6 string literal, e.g. "192.168.0.1" or "2001:db8::1"

Returns:

InetAddress representing the argument

Throws:

IllegalArgumentException - if the argument is not a valid IP string literal

isInetAddress

public static boolean isInetAddress(String ipString)

Parameters:

ipString - String to evaluated as an IP string literal

Returns:

true if the argument is a valid IP string literal

toAddrString

public static String toAddrString(InetAddress ip)

Parameters:

ip - InetAddress to be converted to an address string

Returns:

String containing the text-formatted IP address

Since:

toUriString

public static String toUriString(InetAddress ip)

Returns the string representation of an InetAddress suitable for inclusion in a URI.

For IPv4 addresses, this is identical to InetAddress.getHostAddress() , but for IPv6 addresses it compresses zeroes and surrounds the text with square brackets; for example "[2001:db8::1]" .

Per section 3.2.2 of http://tools.ietf.org/html/rfc3986 , a URI containing an IPv6 string literal is of the form "http://[2001:db8::1]:8888/index.html" .

Use of either toAddrString(java.net.InetAddress) , InetAddress.getHostAddress() , or this method is recommended over InetAddress.toString() when an IP address string literal is desired. This is because InetAddress.toString() prints the hostname and the IP address string joined by a "/".

Parameters:

ip - InetAddress to be converted to URI string literal

Returns:

String containing URI-safe string literal

forUriString

public static InetAddress forUriString(String hostAddr)

Returns an InetAddress representing the literal IPv4 or IPv6 host portion of a URL, encoded in the format specified by RFC 3986 section 3.2.2.

This function is similar to forString(String) , however, it requires that IPv6 addresses are surrounded by square brackets.

This function is the inverse of toUriString(java.net.InetAddress) .

Parameters:

hostAddr - A RFC 3986 section 3.2.2 encoded IPv4 or IPv6 address

Returns:

an InetAddress representing the address in hostAddr

Throws:

IllegalArgumentException - if hostAddr is not a valid IPv4 address, or IPv6 address surrounded by square brackets

isUriInetAddress

public static boolean isUriInetAddress(String ipString)

Returns true if the supplied string is a valid URI IP string literal, false otherwise.

Parameters:

ipString - String to evaluated as an IP URI host string literal

Returns:

true if the argument is a valid IP URI host

isCompatIPv4Address

public static boolean isCompatIPv4Address(Inet6Address ip)

Evaluates whether the argument is an IPv6 "compat" address.

An "IPv4 compatible", or "compat", address is one with 96 leading bits of zero, with the remaining 32 bits interpreted as an IPv4 address. These are conventionally represented in string literals as "::192.168.0.1" , though "::c0a8:1" is also considered an IPv4 compatible address (and equivalent to "::192.168.0.1" ).

For more on IPv4 compatible addresses see section 2.5.5.1 of http://tools.ietf.org/html/rfc4291

NOTE: This method is different from Inet6Address.isIPv4CompatibleAddress() in that it more correctly classifies "::" and "::1" as proper IPv6 addresses (which they are), NOT IPv4 compatible addresses (which they are generally NOT considered to be).

Parameters:

ip - Inet6Address to be examined for embedded IPv4 compatible address format

Returns:

true if the argument is a valid "compat" address

getCompatIPv4Address

public static Inet4Address getCompatIPv4Address(Inet6Address ip)

Returns the IPv4 address embedded in an IPv4 compatible address.

Parameters:

ip - Inet6Address to be examined for an embedded IPv4 address

Returns:

Inet4Address of the embedded IPv4 address

Throws:

IllegalArgumentException - if the argument is not a valid IPv4 compatible address

is6to4Address

public static boolean is6to4Address(Inet6Address ip)

Evaluates whether the argument is a 6to4 address.

6to4 addresses begin with the "2002::/16" prefix. The next 32 bits are the IPv4 address of the host to which IPv6-in-IPv4 tunneled packets should be routed.

For more on 6to4 addresses see section 2 of http://tools.ietf.org/html/rfc3056

Parameters:

ip - Inet6Address to be examined for 6to4 address format

Returns:

true if the argument is a 6to4 address

get6to4IPv4Address

public static Inet4Address get6to4IPv4Address(Inet6Address ip)

Returns the IPv4 address embedded in a 6to4 address.

Parameters:

ip - Inet6Address to be examined for embedded IPv4 in 6to4 address

Returns:

Inet4Address of embedded IPv4 in 6to4 address

Throws:

IllegalArgumentException - if the argument is not a valid IPv6 6to4 address

isTeredoAddress

public static boolean isTeredoAddress(Inet6Address ip)

Evaluates whether the argument is a Teredo address.

Teredo addresses begin with the "2001::/32" prefix.

Parameters:

ip - Inet6Address to be examined for Teredo address format

Returns:

true if the argument is a Teredo address

getTeredoInfo

public static InetAddresses.TeredoInfo getTeredoInfo(Inet6Address ip)

Returns the Teredo information embedded in a Teredo address.

Parameters:

ip - Inet6Address to be examined for embedded Teredo information

Returns:

extracted TeredoInfo

Throws:

IllegalArgumentException - if the argument is not a valid IPv6 Teredo address

isIsatapAddress

public static boolean isIsatapAddress(Inet6Address ip)

Evaluates whether the argument is an ISATAP address.

From RFC 5214: "ISATAP interface identifiers are constructed in Modified EUI-64 format [...] by concatenating the 24-bit IANA OUI (00-00-5E), the 8-bit hexadecimal value 0xFE, and a 32-bit IPv4 address in network byte order [...]"

For more on ISATAP addresses see section 6.1 of http://tools.ietf.org/html/rfc5214

Parameters:

ip - Inet6Address to be examined for ISATAP address format

Returns:

true if the argument is an ISATAP address

getIsatapIPv4Address

public static Inet4Address getIsatapIPv4Address(Inet6Address ip)

Returns the IPv4 address embedded in an ISATAP address.

Parameters:

ip - Inet6Address to be examined for embedded IPv4 in ISATAP address

Returns:

Inet4Address of embedded IPv4 in an ISATAP address

Throws:

IllegalArgumentException - if the argument is not a valid IPv6 ISATAP address

hasEmbeddedIPv4ClientAddress

public static boolean hasEmbeddedIPv4ClientAddress(Inet6Address ip)

Examines the Inet6Address to determine if it is an IPv6 address of one of the specified address types that contain an embedded IPv4 address.

NOTE: ISATAP addresses are explicitly excluded from this method due to their trivial spoofability. With other transition addresses spoofing involves (at least) infection of one's BGP routing table.

Parameters:

ip - Inet6Address to be examined for embedded IPv4 client address

Returns:

true if there is an embedded IPv4 client address

Since:

getEmbeddedIPv4ClientAddress

public static Inet4Address getEmbeddedIPv4ClientAddress(Inet6Address ip)

Examines the Inet6Address to extract the embedded IPv4 client address if the InetAddress is an IPv6 address of one of the specified address types that contain an embedded IPv4 address.

NOTE: ISATAP addresses are explicitly excluded from this method due to their trivial spoofability. With other transition addresses spoofing involves (at least) infection of one's BGP routing table.

Parameters:

ip - Inet6Address to be examined for embedded IPv4 client address

Returns:

Inet4Address of embedded IPv4 client address

Throws:

IllegalArgumentException - if the argument does not have a valid embedded IPv4 address

isMappedIPv4Address

public static boolean isMappedIPv4Address(String ipString)

Evaluates whether the argument is an "IPv4 mapped" IPv6 address.

An "IPv4 mapped" address is anything in the range ::ffff:0:0/96 (sometimes written as ::ffff:0.0.0.0/96), with the last 32 bits interpreted as an IPv4 address.

For more on IPv4 mapped addresses see section 2.5.5.2 of http://tools.ietf.org/html/rfc4291

Note: This method takes a String argument because InetAddress automatically collapses mapped addresses to IPv4. (It is actually possible to avoid this using one of the obscure Inet6Address methods, but it would be unwise to depend on such a poorly-documented feature.)

Parameters:

ipString - String to be examined for embedded IPv4-mapped IPv6 address format

Returns:

true if the argument is a valid "mapped" address

Since:

getCoercedIPv4Address

public static Inet4Address getCoercedIPv4Address(InetAddress ip)

Coerces an IPv6 address into an IPv4 address.

HACK: As long as applications continue to use IPv4 addresses for indexing into tables, accounting, et cetera, it may be necessary to coerce IPv6 addresses into IPv4 addresses. This function does so by hashing the upper 64 bits into 224.0.0.0/3 (64 bits into 29 bits).

A "coerced" IPv4 address is equivalent to itself.

NOTE: This function is failsafe for security purposes: ALL IPv6 addresses (except localhost (::1)) are hashed to avoid the security risk associated with extracting an embedded IPv4 address that might permit elevated privileges.

Parameters:

ip - InetAddress to "coerce"

Returns:

Inet4Address represented "coerced" address

Since:

coerceToInteger

public static int coerceToInteger(InetAddress ip)

Returns an integer representing an IPv4 address regardless of whether the supplied argument is an IPv4 address or not.

IPv6 addresses are coerced to IPv4 addresses before being converted to integers.

As long as there are applications that assume that all IP addresses are IPv4 addresses and can therefore be converted safely to integers (for whatever purpose) this function can be used to handle IPv6 addresses as well until the application is suitably fixed.

NOTE: an IPv6 address coerced to an IPv4 address can only be used for such purposes as rudimentary identification or indexing into a collection of real InetAddress es. They cannot be used as real addresses for the purposes of network communication.

Parameters:

ip - InetAddress to convert

Returns:

int , "coerced" if ip is not an IPv4 address

Since:

fromInteger

public static Inet4Address fromInteger(int address)

Returns an Inet4Address having the integer value specified by the argument.

Parameters:

address - int , the 32bit integer address to be converted

Returns:

Inet4Address equivalent of the argument

fromLittleEndianByteArray

public static InetAddress fromLittleEndianByteArray(byte[] addr)
                                             throws UnknownHostException

Returns an address from a little-endian ordered byte array (the opposite of what InetAddress.getByAddress(java.lang.String, byte[]) expects).

IPv4 address byte array must be 4 bytes long and IPv6 byte array must be 16 bytes long.

Parameters:

addr - the raw IP address in little-endian byte order

Returns:

an InetAddress object created from the raw IP address

Throws:

UnknownHostException - if IP address is of illegal length

decrement

public static InetAddress decrement(InetAddress address)

Returns a new InetAddress that is one less than the passed in address. This method works for both IPv4 and IPv6 addresses.

Parameters:

address - the InetAddress to decrement

Returns:

a new InetAddress that is one less than the passed in address

Throws:

IllegalArgumentException - if InetAddress is at the beginning of its range

Since:

increment

public static InetAddress increment(InetAddress address)

Returns a new InetAddress that is one more than the passed in address. This method works for both IPv4 and IPv6 addresses.

Parameters:

address - the InetAddress to increment

Returns:

a new InetAddress that is one more than the passed in address

Throws:

IllegalArgumentException - if InetAddress is at the end of its range

Since:

isMaximum

public static boolean isMaximum(InetAddress address)

Returns true if the InetAddress is either 255.255.255.255 for IPv4 or ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff for IPv6.

Returns:

true if the InetAddress is either 255.255.255.255 for IPv4 or ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff for IPv6

Since: