IPv6 address examples for different IPv6 address representations and types

IPv6 addresses are 128-bit identifiers for interfaces and sets of interfaces (RFC 4291). In its full notation, an IPv6 address is represented in eight groups of four hexadecimal digits (eight 16-bit blocks) separated by colons (:), for example

2001:0db8:0a0b:12f0:0000:0000:0000:0001

RFC 5952 recommends to use the compressed format for IPv6 address textual representation:

2001:db8:a0b:12f0::1

• Leading zeros MUST be suppressed.
For example, 2001:0db8::0001 is not acceptable and must be represented as 2001:db8::1

• The use of the symbol "::" MUST be used to its maximum capability.
For example, 2001:db8:0:0:0:0:2:1 must be shortened to 2001:db8::2:1.

• The symbol "::" MUST NOT be used to shorten just one 16-bit 0 field.
For example, the representation 2001:db8:0:1:1:1:1:1 is correct, but 2001:db8::1:1:1:1:1 is not correct.

• The characters "a", "b", "c", "d", "e", and "f" in an IPv6 address MUST be represented in lowercase.

IPv6 address formats for usage with applications

IPv6 addresses in URLs

In resource identifiers like URIs and URLs, the colon (:) character is used to separate the IP address from the port number. As the literal representation of IPv6 addresses contains colon characters, this might cause conflicts. Because of this, literal IPv6 addresses are enclosed in "[" and "]" (square) brackets.

In an URL, the IPv6 address should be enclosed in square brackets [rfc3986]:

http://[2001:db8:a0b:12f0::1]/index.html

http://[2001:db8:a0b:12f0::1]:80/index.html

IPv6 addresses including a port number

IPv6 addresses including a port number should be enclosed in square brackets [rfc5952] [rfc3986]:

[2001:db8:a0b:12f0::1]:21

IPv6 addresses with prefix

The prefix is appended to the IPv6 address separated by a slash "/" character (CIDR notation) [rfc4291]:

2001:db8:a0b:12f0::1/64

IPv6 addresses including a zone identifier (zone index)

A zone identifier within an IPv6 address should be specified separated by "%" (percent) character [rfc4007]:

2001:db8:a0b:12f0::1%eth0

Example SSH:

ssh username@2001:db8:a0b:12f0::1%eth0

Example SCP:

scp file.txt username@[2001:db8:a0b:12f0::1%eth0]/path/

IPv6 addresses in URIs including a zone identifier (zone index)

A zone identifier within an IPv6 address in URIs should be specified separated by "%25" ("%25" is the percent-encoded representation of a literal "%" symbol) [rfc6874]:

2001:db8:a0b:12f0::1%25eth0 or

[2001:db8:a0b:12f0::1%25eth0]:21

RFC 6874 suggests that URI parsers (for example in browsers) accept bare "%" signs when possible:

[2001:db8:a0b:12f0::1%eth0]:80

IP6.ARPA addresses

The IP6.ARPA domain is defined to look up a record given an IPv6 address. The intent of this domain is to provide a way of mapping an IPv6 address to a host name [rfc3596].

The IP6.ARPA address can be formed by the hexadecimal values of an IPv6 address in full notation in reverse order, separated by a dot "." and terminated by the domain "IP6.ARPA".

For example, the IP6.ARPA address of 2001:0db8:0a0b:12f0:0000:0000:0000:0001 would be

1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.f.2.1.b.0.a.0.8.b.d.0.1.0.0.2.IP6.ARPA

Windows UNC (Uniform Naming Convention) path name notation

UNC path names (\\server_ip\share) do not support the colon character. For this reason, Microsoft has created a transcription algorithm to represent IPv6 addresses in UNC path names. Addresses in this notation are directly resolved by Microsoft software without DNS queries. To transcribe an address to this format, replace all colons with dashes (-) and append the second-level domain "ipv6-literal.net" separated by a dot to the address.

2001-db8-a0b-12f0--1.ipv6-literal.net

The "%" sign to specify a zone index is replaced by an "s" character:

2001-db8-a0b-12f0--1s4.ipv6-literal.net

For example, to access the \Misc directory on the server 2001:db8:a0b:12f0::1 use the UNC path \\2001-db8-a0b-12f0--1s4.ipv6-literal.net\Misc.

Other IPv6 address representations

Integer format

The integer ID of 2001:db8:a0b:12f0::1 is 42540766414390830568948465903729639425

Hexadecimal ID

The hexadecimal ID of 2001:db8:a0b:12f0::1 is 0x20010db80a0b12f00000000000000001

Dotted Decimal ID

The dotted decimal ID of 2001:db8:a0b:12f0::1 is 32.1.219.8.10.11.18.240.0.0.0.0.0.0.0.1

Base 85 ID

The base 85 ID of 2001:db8:a0b:12f0::1 is 9r}Vstbyz7$19|O(~JT0 [rfc1924]

Binary ID

The binary ID of 2001:db8:a0b:12f0::1 is 00100000000000010000110110111000000010100000101100010010111100000000000000000000000000000000000000000000000000000000000000000001

Use a subnet calculator to show more address details.

Fig. 1: IPv6 address processed in GestióIP's online subnet calculator

IPv6 address types

RFC 4291 defines three types of IPv6 addresses:

Unicast

An identifier for a single interface. A packet sent to a unicast address is delivered to the interface identified by that address.

An example for an IPv6 unicast address is 3731:54:65fe:2::a7

Anycast

An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to an anycast address is delivered to one of the interfaces identified by that address (the "nearest" one, according to the routing protocols' measure of distance).

Anycast addresses are allocated from the unicast address space and are not syntactically distinguishable from unicast addresses. Assigning an unicast address to more than one interface makes an unicast address an anycast address. Nodes must be explicitly configured to recognize that an address is an anycast address.

Anycast can be used to increase the avilability and speed of critical servers. All Internet root nameservers are implemented as clusters of hosts using anycast addressing. Anycast is also used by IPv6 transition mechanisms and Content Delivery Networks [rfc7094].

An example for an IPv6 anycast address is 3731:54:65fe:2::a8

Multicast

An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to a multicast address is delivered to all interfaces identified by that address.

An example for an IPv6 multicast address is FF01:0:0:0:0:0:0:1

There are no broadcast addresses in IPv6, their function being superseded by multicast addresses.

IPv6 address scopes

Every IPv6 address other than the unspecified address (::) has a specific scope. A scope is a topological span within which the address may be used as a unique identifier for an interface or set of interfaces [rfc4007].

An IPv6 interface is expected to have multiple IPv6 addresses from different scopes associated with it. This is a key difference to IPv4, where an interface has typically only a single address assigned. IPv6 interfaces always have a link local address and typically one or more of a unique local (ULA) or globally unique address.

Global Unicast Address Scope

The IPv6 Global Unicast space encompasses the entire IPv6 address scope. Exceptions are the multicast range ff00::/8 and those ranges, which have been allocated for other purposes (see table "IPv6 Special-Purpose Addresses"). It is thought for uniquely identifying interfaces anywhere in the Internet.

IANA unicast address assignments are currently limited to the IPv6 unicast address range of 2000::/3 [IANA].

IPv6 Special-Purpose Addresses [IANA][rfc6890][rfc8190]

Other IPv6 addresses

EUI-64 addresses [rfc4291] (used in Stateless Address Autoconfiguration (SLAAC) [rfc4862])

SLAAC allows a host to generate its own (global) addresses using a combination of locally available information (e.g. interface's MAC address) and information advertised by routers. Routers advertise prefixes that identify the subnet(s) associated with a link, while hosts generate an "interface identifier" that uniquely identifies an interface on a subnet. An address is formed by combining the two. In the absence of routers, a host can only generate link-local addresses. However, link-local addresses are sufficient for allowing communication among nodes attached to the same link. The SLACC mechanism is one of the key benefits of IPv6 over IPv4 because it eliminates the need of DHCP or manual configuration.

There are different approaches for creating EUI-64 addresses. An example is an EUI-64 address with embedded MAC address [rfc4862].

IPv6 EUI-64 address's "interface identifier" with embedded MAC addresses are formed by inserting the hex value fffe in the middle of the MAC address and inverting the 7. bit of the MAC address. Here an example of an EUI-64 address created from the MAC address 12:34:56:78:90:00:

2001:db8:a:a:1034:56ff:fe78:9000

IPv6 Multicast addresses

IPv6 Multicast is a mechanism for transmitting information from a single source to many receivers. An IPv6 multicast address is an identifier for a group of interfaces (typically on different nodes). An interface may belong to any number of multicast groups [rfc4291]. IPv6 Multicast addresses fall under the range ff00::/8 ([rfc2375][IANA]).

Multicast scopes ([rfc4291][rfc7346])

IPv6 multicast addresses are limited to scopes. The scopes are determined by the value of the 4th nibble (bits 13-16) of the multicast address (ff0X::/8).

RFC 7346, which updates RFC 4291, defines the following values:

0 - reserved

1 - Interface-Local scope spans only a single interface on a node, and is useful only for loopback transmission of multicast. Packets with interface-local scope received from another node must be discarded.

2 - Link-Local multicast scopes span the same topological region as the corresponding unicast scope.

3 - Realm-Local. The definition of any Realm-Local scope for a particular network technology should be published in an RFC.

4 - Admin-Local scope is the smallest scope that must be administratively configured, i.e., not automatically derived from physical connectivity or other, non- multicast-related configuration.

5 - Site-Local scope is intended to span a single site.

6 and 7 are unasigned

8 - Organization-Local scope is intended to span multiple sites belonging to a single organization.

9 to D are unasigned

E - Global scope.

F - reserved

IPv6 Multicast addresses examples

For example, if the "NTP servers group" is assigned a permanent multicast address with a group ID of 101 (hex), then

FF01:0:0:0:0:0:0:101 means all NTP servers on the same interface (i.e., the same node) as the sender.

FF02:0:0:0:0:0:0:101 means all NTP servers on the same link as the sender.

FF05:0:0:0:0:0:0:101 means all NTP servers in the same site as the sender.

FF0E:0:0:0:0:0:0:101 means all NTP servers in the Internet.

Usage Examples

Discover all nodes on the same link (link-local scope) using the "All Nodes Address":

ping6 -I eth0 ff02::1

PING ff02::1(ff02::1) from fe80::74e6:b5f3:fe92:830e eth0: 56 data bytes
64 bytes from fe80::6ae3:b5ff:fe92:330e: icmp_seq=1 ttl=64 time=0.037 ms
64 bytes from fe80::20ab:16d8:a479:238d: icmp_seq=1 ttl=64 time=0.537 ms
64 bytes from fe80::2a1:9bff:fe9b:f268: icmp_seq=1 ttl=64 time=0.545 ms
64 bytes from fe80::1c60:4bff:fa71:1a56: icmp_seq=1 ttl=64 time=0.561 ms
64 bytes from fe80::2a3:aeff:fe53:743e: icmp_seq=1 ttl=64 time=0.565 ms
...

Ping all NTP server on the same site (site-local scope):

ping6 -I eth0 ff05::101

PING ff05::101(ff05::101) from 2001:db8::a:74e6:b5f3:fe92:830e eth0: 56 data bytes
64 bytes from 2001:db8::b:2f4:4bff:fa71:1a56: icmp_seq=1 ttl=64 time=0.561 ms
64 bytes from 2001:db8::c:69b:aeff:fe53:743e: icmp_seq=1 ttl=64 time=0.565 ms
...