About IPv6

Internet Protocol Version 6 (IPv6) is the latest version of Internet Protocol and the successor to IPv4.

IPv6 uses 128-bit addresses, which means it supports a much larger number of addresses than IPv4. IPv4 uses 32-bit addresses. A larger IPv6 address space is important because the IPv4 address space is limited. As demand for IP addresses increases worldwide, the IPv4 address space faces eventual depletion.

To learn about the IPv6 protocol and why you might use it on your network, see the IPv6 Fundamentals video tutorial (10 minutes).

To learn how the Firebox uses IPv6, see the IPv6 on the Firebox video tutorial (10 minutes).

For information about Fireware features that support IPv6, see About IPv6 Support in Fireware.

IPv6 Addressing

IPv6 Address Format

An IPv6 address contains eight groups of 16-bit hexadecimal values, separated by colons (:). The hexadecimal digits are not case-sensitive. Some examples of IPv6 addresses are:

  • 2561:1900:4545:0003:0200:F8FF:FE21:67CF
  • 2260:F3A4:32CB:715D:5D11:D837:FC76:12FC
  • FE80:0000:0000:0000:2045:FAEB:33AF:8374

The first four groups of 16-bit hexadecimal values represent the network. The last four groups of 16-bit hexadecimal values are the interface ID that uniquely identifies each networked device. This value is usually derived from the MAC address of the device.

You cannot use these special-purpose IP addresses as an IPv6 interface address:

  • IP addresses that start with 2002, unless bits 17–48 specify a valid IPv4 address
  • IP addresses that start with FE80 (specifies a link local address)
  • IP addresses that start with FEC0 (specifies a site local address)
  • IP addresses that start with FF(used for IPv6 multicast addresses)

Shorten an IPv6 Address

There are two ways you can shorten the notation of an IPv6 address:

  • Remove leading zeros — In each 16-bit hexadecimal address group, you can remove the leading zeros. For example, these two IPv6 addresses are equivalent:



  • Remove groups of zeros — If an IPv6 address contains adjacent groups of 16-bit hexadecimal values that are all zeros (0000), you can replace one group of adjacent blocks of zeros with two colons (::). For example, these two IPv6 addresses are equivalent:



You can use two colons (::) only once in an IPv6 address to represent adjacent groups with all zeros.

IPv6 Prefix

The IPv6 prefix indicates the subnet associated with an IPv6 address. The prefix is expressed as a slash (/) followed by the prefix size, which is a decimal number between 1 and 128. The prefix size indicates how many bits of the address make up the network identifier prefix. Examples of IPv6 prefixes are:

  • /64 — Prefix used for a single subnet
  • /48 — Prefix used for a site that could have multiple subnets

Configure IPv6

To configure IPv6, see Configure IPv6.

See Also

About Slash Notation