§ — — Data Communications and Networking
IPv6 was developed to solve IPv4 address exhaustion and to improve long-term internet growth. IPv6 uses 128-bit addresses, which provide a much larger address space than IPv4.
IPv4 has a limited number of addresses. Techniques such as NAT and private addressing helped extend IPv4 usage, but they did not remove the need for a larger addressing system. IPv6 provides enough address space for modern networks, mobile devices, cloud systems, and future growth.
An IPv6 address is written in hexadecimal and divided into eight groups called hextets.
Example:
2001:0db8:0000:0001:0000:0000:0000:000A
Each hextet represents 16 bits.
Leading zeros in a hextet may be removed.
2001:0db8:0000:0001:0000:0000:0000:000A
2001:db8:0:1:0:0:0:A
One continuous sequence of all-zero hextets may be replaced with ::. This shortcut can be used only once in an address.
2001:db8:0:1:0:0:0:A
2001:db8:0:1::A
Using :: more than once would make the address ambiguous.
| Type | Purpose |
|---|---|
| Global Unicast Address (GUA) | Publicly routable IPv6 address. |
| Link-Local Address (LLA) | Used on the local link; not routed beyond it. |
| Multicast Address | Sent to a group of IPv6 devices. |
| Anycast Address | Assigned to multiple devices; traffic goes to the nearest one according to routing. |
IPv6 does not use broadcast. Multicast and Neighbor Discovery provide functions that replace many broadcast uses.
A typical IPv6 GUA contains:
| Part | Purpose |
|---|---|
| Global routing prefix | Assigned by provider or organization; identifies the larger network. |
| Subnet ID | Identifies subnets inside the organization. |
| Interface ID | Identifies a specific interface on a subnet. |
A link-local address is required on IPv6-enabled interfaces. It is used for communication on the same local link, including neighbor discovery and routing protocol communication.
Link-local addresses commonly begin with:
fe80::/10
An IPv6 address can be configured manually. A device may also use automatic methods for address creation.
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IPv6 devices may create or receive addresses using methods such as Stateless Address Autoconfiguration (SLAAC), DHCPv6, or a combination of both. Routers can advertise network prefix information so hosts can create their own addresses.
IPv6 multicast addresses begin with ff00::/8. Common groups include:
| Address | Group |
|---|---|
| ff02::1 | All IPv6 nodes on the local link. |
| ff02::2 | All IPv6 routers on the local link. |
Solicited-node multicast addresses are used by Neighbor Discovery to perform efficient address resolution.
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