Unicast addressing is a fundamental concept in IPv6 networking where packets are sent from one source to exactly one destination. There are three main types of unicast addresses that CCNA candidates must understand.
Global Unicast Addresses are the IPv6 equivalent of public IPv4 addresses. They ar…Unicast addressing is a fundamental concept in IPv6 networking where packets are sent from one source to exactly one destination. There are three main types of unicast addresses that CCNA candidates must understand.
Global Unicast Addresses are the IPv6 equivalent of public IPv4 addresses. They are globally routable and unique across the entire internet. These addresses typically begin with 2000::/3, meaning they start with binary bits 001. Organizations receive global unicast addresses from their Internet Service Providers or Regional Internet Registries. The structure includes a global routing prefix, subnet ID, and interface ID, allowing for hierarchical addressing and efficient routing.
Unique Local Addresses (ULA) serve a similar purpose to private IPv4 addresses (like 10.x.x.x or 192.168.x.x). They use the prefix FC00::/7, with most implementations using FD00::/8. These addresses are routable within an organization but are not intended for internet routing. ULAs provide a way for enterprises to create their own internal addressing schemes that remain consistent even if they change ISPs. They offer address independence and can be used for internal communications that should never traverse public networks.
Link-Local Addresses are mandatory for every IPv6-enabled interface and are automatically configured. They use the prefix FE80::/10 and are only valid within a single network segment or link. These addresses cannot be routed beyond the local subnet, making them essential for neighbor discovery, router discovery, and other local network operations. Every IPv6 device generates its link-local address using either EUI-64 format or random generation methods.
Understanding these three unicast address types is crucial for network configuration, troubleshooting, and design. Each serves a specific purpose in the IPv6 architecture, from global internet communication to local network operations.
IPv6 Unicast Address Types: Global, Unique Local, and Link-Local
Why IPv6 Unicast Types Are Important
Understanding IPv6 unicast address types is essential for the CCNA exam and real-world networking. IPv6 is the successor to IPv4, designed to address the exhaustion of IPv4 addresses. Each unicast type serves a specific purpose in network communication, and knowing when to use each type is critical for network design, troubleshooting, and security.
What Are IPv6 Unicast Address Types?
IPv6 unicast addresses identify a single interface. When a packet is sent to a unicast address, it is delivered to that specific interface. There are three main types:
1. Global Unicast Addresses (GUA) These are the IPv6 equivalent of public IPv4 addresses. They are globally routable and unique across the entire internet. - Prefix: 2000::/3 (addresses beginning with 2 or 3) - Structure: 48-bit global routing prefix + 16-bit subnet ID + 64-bit interface ID - Used for communication across the internet
2. Unique Local Addresses (ULA) These are similar to IPv4 private addresses (10.x.x.x, 172.16.x.x, 192.168.x.x). They are routable within an organization but not on the public internet. - Prefix: FC00::/7 (typically FD00::/8 is used in practice) - Used for internal network communication - Not routable on the global internet
3. Link-Local Addresses (LLA) These addresses are automatically assigned to every IPv6-enabled interface and are only valid on the local link (subnet). - Prefix: FE80::/10 - Cannot be routed beyond the local network segment - Required for IPv6 operation (neighbor discovery, routing protocols) - Automatically generated using EUI-64 or random interface ID
How IPv6 Unicast Addressing Works
When a device communicates using IPv6: - Link-local addresses are used for local segment communication, including router advertisements and neighbor discovery - Global unicast addresses are used when devices need to communicate across the internet - Unique local addresses are used for internal organizational traffic that should remain private
A single interface can have multiple IPv6 addresses simultaneously - typically at least one link-local and one global unicast address.
Key Characteristics Summary
| Type | Prefix | Scope | Routable Globally | |------|--------|-------|-------------------| | Global Unicast | 2000::/3 | Internet | Yes | | Unique Local | FC00::/7 | Organization | No | | Link-Local | FE80::/10 | Local Link | No |
Exam Tips: Answering Questions on IPv6 Unicast Types
Tip 1: Memorize the Prefixes - Global: starts with 2 or 3 - Unique Local: starts with FC or FD - Link-Local: starts with FE80
Tip 2: Understand Scope When a question asks about reaching a remote network across the internet, the answer involves global unicast. For internal-only traffic, consider unique local. For same-segment communication, think link-local.
Tip 3: Remember Link-Local is Mandatory Every IPv6-enabled interface must have a link-local address. This is essential for routing protocols like OSPFv3 and EIGRP for IPv6.
Tip 4: Watch for Routing Questions Link-local addresses cannot be used as destination addresses for traffic leaving the local subnet. Routers use link-local addresses as next-hop addresses.
Tip 5: Compare to IPv4 Equivalents - Global Unicast = Public IPv4 - Unique Local = Private IPv4 (RFC 1918) - Link-Local = APIPA (169.254.x.x) but more important in IPv6
Tip 6: Configuration Awareness Link-local addresses can be manually configured or auto-generated. Global unicast addresses can be assigned via SLAAC, DHCPv6, or manual configuration.