IPAddress::IPv6::Mapped

It is usually identified as a IPv4 mapped IPv6 address, a particular IPv6 address which aids the transition from IPv4 to IPv6. The structure of the address is

::ffff:w.y.x.z

where w.x.y.z is a normal IPv4 address. For example, the following is a mapped IPv6 address:

::ffff:192.168.100.1

IPAddress is very powerful in handling mapped IPv6 addresses, as the IPv4 portion is stored internally as a normal IPv4 object. Let's have a look at some examples. To create a new mapped address, just use the class builder itself

ip6 = IPAddress::IPv6::Mapped.new "::ffff:172.16.10.1/128"

or just use the wrapper method

ip6 = IPAddress.new "::ffff:172.16.10.1/128"

Let's check it's really a mapped address:

ip6.mapped?   # => true
ip6.to_string # => "::ffff:172.16.10.1/128"

Now with the ipv4 attribute, we can easily access the IPv4 portion of the mapped IPv6 address:

ip6.ipv4.address # => "172.16.10.1"

Internally, the IPv4 address is stored as two 16 bits groups. Therefore all the usual methods for an IPv6 address are working perfectly fine:

ip6.to_hex  # => "00000000000000000000ffffac100a01"
ip6.address # => "0000:0000:0000:0000:0000:ffff:ac10:0a01"

A mapped IPv6 can also be created just by specify the address in the following format:

ip6 = IPAddress.new "::172.16.10.1"

That is, two colons and the IPv4 address. However, as by RFC, the ffff group will be automatically added at the beginning

ip6.to_string # => "::ffff:172.16.10.1/128"

making it a mapped IPv6 compatible address.