IPv6 - Explanation

Can be truncated

0
- You can remove any zeros at the start of a hextet.
- You must leave at least one digit if the entire hextet is 0000 (it becomes 0).
- You cannot remove trailing zeros or zeros in the middle of a hextet.
Double Colon (::): Can only be used once in an entire address to replace a single continuous chain of all-zero hextets.

Communication models

Unicast
Multicast
Anycast

An IPv6 address

8 groups
4 hexadecimal digits per group
Colons between each group

Address types

GUA (Global Unicast Address)

Definition: These are globally routable addresses and unique across the entire internet.
Prefix: 2000::/3 (2000 to 3fff).
Prefix Binary: 001
/32 delegation by example 2001:db8:

Example:

Section	Bits	Example Binary	Example Hex	Purpose	Issuer
GUA Prefix	3	`0010000000000000`	`2000` (start of `2000::/3`)	Defines the address type as Global Unicast	RFC
ISP Prefix	29	`0000000000000001`	`1`	Defines ISP range	IR like RIPE
Site Prefix	16	`0000110110111000`	`0db8`	Identifies the specific organization's assigned block	ISP
Network ID	48	`0010000000000001 0000110110111000`	`2001:0db8`	Combined GUA + ISP and Site used for global routing	RFC + IR + ISP
Subnet ID	16	`0000000000000001`	`0001`	Identifies an internal subnet	IT department
Interface Identifier	64	`0000000000000000000000000000000000000000000000000000000000000001`	`0000:0000:0000:0001`	Identifies the specific interface or host	MAC or random

Note: The 3-bit GUA Prefix (001) indicates the 2000::/3 range. The subsequent 45 bits are assigned by the registry to the organization. Together, they form the standard 48-bit Global Routing Prefix used in routing tables.

ULA (Unique Local Address)
- Definition: These are private, non-globally routable addresses. They are intended for use within a single site or organization and are not routed in the global internet.
- Prefix: fc00::/7 (specifically fd00::/8 for locally assigned addresses, while fc00::/8 is reserved for future definition).
- Prefix Binary: 1111110
- Usage: Used for internal network communication, such as connecting servers within a data center or devices in a home network that do not need direct internet exposure. IPv6 networks often run ULA alongside GUA.
- Benefit: They allow internal networking to continue functioning even if the internet connection or global prefix changes.
LLA (Link-Local Address)
- Definition: These addresses are valid only on a single physical or logical link (subnet). They are not routable beyond the local segment; routers will never forward packets with LLA source or destination addresses.
- Prefix: fe80::/10.
- Prefix Binary: 1111111010
- Usage: Mandatory for every IPv6 interface. They are used for essential local network operations like Neighbor Discovery Protocol (NDP), Router Advertisement (RA), and as the next-hop address in routing tables. Even if a host has no GUA or ULA, it will always have an LLA.
- Generation: Typically automatically generated using the FE80 prefix and the interface's MAC address (EUI-64) or a random value.
Multicast
- Definition: Used to send a single packet to multiple destinations simultaneously (one-to-many). IPv6 relies heavily on multicast for functions that IPv4 handled with broadcast.
- Prefix: ff00::/8.
- Prefix Binary: 11111111
- Usage: Critical for network operations. Examples include: ff02::1: All nodes on the local link. ff02::2: All routers on the local link. ff02::1:ffXX:XXXX: Solicited-node multicast addresses used for efficient Neighbor Discovery (replacing ARP).
Loopback Address (::1/128): Used by a node to send a packet to itself.
Unspecified Address (::/128): Used by a host when it has not yet been assigned an address (e.g., during the Duplicate Address Detection process).
Documentation Address: 2001:db8::/32
NAT64 Address Prefix: 64:ff9b::/96

External Links

IPv6 Addressing Architecture — RFC 4291 https://datatracker.ietf.org/doc/html/rfc4291
IPv6 Stateless Address Autoconfiguration — RFC 4862 https://datatracker.ietf.org/doc/html/rfc4862
IPv6 Address Assignment to End Sites — RFC 6177 https://datatracker.ietf.org/doc/html/rfc6177
Unique Local IPv6 Unicast Addresses — RFC 4193 https://datatracker.ietf.org/doc/html/rfc4193
RIPE NCC — IPv6 Address Allocation and Assignment Policy https://www.ripe.net/publications/docs/ripe-738/
APNIC — IPv6 Address Planning https://www.apnic.net/community/ipv6-program/ipv6-address-planning/
ARIN — IPv6 Address Planning https://www.arin.net/resources/guide/ipv6/first_request

Expired

DHCPv4 Option for IPv4 routes with IPv6 nexthops