📘 CCNA 200-301 v1.1
1.9 Describe IPv6 address types
1.9.a Unicast (global, unique local, and link local)
IPv6 (Internet Protocol version 6) is the next generation of IP addressing, created to replace IPv4 because IPv4 addresses were running out.
IPv6 uses 128-bit addresses, which means there are a huge number of unique addresses available — enough for every device on Earth and more.
IPv6 addresses are written in hexadecimal (base 16) and separated by colons (:) instead of dots like IPv4.
Example:
2001:0db8:0000:0000:0000:ff00:0042:8329
(This can be shortened using rules, but the format remains the same.)
IPv6 Address Types Overview
IPv6 addresses are grouped into three major types:
| Type | Purpose |
|---|---|
| Unicast | Identifies a single interface (one device). |
| Multicast | Identifies a group of interfaces. One packet is sent to many devices. |
| Anycast | Identifies multiple interfaces, but data is delivered to the nearest one (based on routing). |
For this section (1.9.a), we’ll focus only on Unicast addresses and their three subtypes.
1.9.a Unicast Addresses
A Unicast IPv6 address identifies a single device (interface) on the network.
When a packet is sent to a unicast address, it goes to one specific destination device — not to multiple devices.
There are three main Unicast types:
- Global Unicast Address (GUA)
- Unique Local Address (ULA)
- Link-Local Address
1️⃣ Global Unicast Address (GUA)
Purpose:
Used for communication over the Internet (similar to public IPv4 addresses).
Range:
Starts with 2000::/3, meaning any address starting with binary 001 (from 2000:: to 3fff:ffff:ffff:ffff:ffff:ffff:ffff:ffff).
Example:
2001:db8::1
Structure (128 bits total):
| Global Routing Prefix | Subnet ID | Interface ID |
| (48 bits) | (16 bits) | (64 bits) |
- Global Routing Prefix – Assigned by an ISP. Identifies your organization’s network on the internet.
- Subnet ID – Used by your organization to create internal subnets.
- Interface ID – Uniquely identifies a device within that subnet (usually based on MAC address or assigned manually).
Example in IT environment:
A company connected to the internet uses Global Unicast Addresses for their servers, routers, and public web systems so they can be reached globally.
Key Points for Exam:
- Globally routable (can cross the Internet).
- Assigned by ISPs or IANA (Internet Assigned Numbers Authority).
- Equivalent to public IPv4 addresses.
- Prefix always begins with
2000::/3.
2️⃣ Unique Local Address (ULA)
Purpose:
Used for internal communication within an organization, not routable on the Internet — similar to private IPv4 addresses.
Range:
Starts with FD00::/8 (some older documentation also mentions FC00::/7).
Example:
FD12:3456:789A::1
Structure:
| Prefix (FD) | Global ID (40 bits) | Subnet ID (16 bits) | Interface ID (64 bits) |
- Prefix (FD) – Indicates it’s a ULA address.
- Global ID – Randomly generated number to make the address unique inside your network.
- Subnet ID – Used to divide internal networks (like departments, VLANs, etc.).
- Interface ID – Identifies the individual device.
Example in IT environment:
Used in corporate networks, data centers, or lab networks for internal communication between routers, servers, and workstations. These addresses are not reachable from the Internet.
Key Points for Exam:
- Similar purpose to IPv4 private addresses (like 10.0.0.0/8 or 192.168.0.0/16).
- Not advertised on the Internet.
- Starts with
FD00::/8. - Can be used for internal routing (OSPFv3, EIGRP for IPv6, etc.).
3️⃣ Link-Local Address
Purpose:
Used for communication between devices on the same local network segment (link).
They are automatically configured on every IPv6-enabled interface — no need for DHCP or manual setup.
Range:
Always starts with FE80::/10.
Example:
FE80::1
Structure:
| Prefix (FE80::/10) | Interface ID (64 bits) |
- Prefix (FE80) – Indicates a link-local address.
- Interface ID – Uniquely identifies the device on the local network.
How it’s used:
- Routers and switches use Link-Local addresses for neighbor discovery and routing protocols (like OSPFv3, EIGRPv6, etc.).
- Devices communicate with others on the same link only — packets cannot be routed beyond that link.
Example in IT environment:
When two routers are connected directly through an interface, they use Link-Local addresses to exchange routing updates.
For example:
Router1 FE80::1 <—> Router2 FE80::2
Even if no global IPv6 addresses are assigned, they can still form a neighbor relationship and communicate locally.
Key Points for Exam:
- Automatically assigned when IPv6 is enabled.
- Always starts with
FE80::/10. - Required for all IPv6-enabled interfaces.
- Cannot be routed outside the local link.
- Used by routing protocols and network discovery.
Summary Table: IPv6 Unicast Types
| Type | Prefix | Scope | Routable on Internet | Assigned By | Example Use |
|---|---|---|---|---|---|
| Global Unicast | 2000::/3 | Global | Yes | ISP / IANA | Public servers, routers |
| Unique Local | FD00::/8 | Organization | No | Admin (local) | Internal communication |
| Link-Local | FE80::/10 | Local link | No | Automatic | Router neighbor discovery |
How to Verify in Cisco IOS
You can verify IPv6 unicast addresses using the following commands:
1. Show IPv6 interfaces:
R1# show ipv6 interface brief
Output example:
GigabitEthernet0/0 [up/up]
FE80::1 (link-local)
2001:DB8:1::1 (global unicast)
FD12:3456:789A::1 (unique local)
2. Ping IPv6 address:
R1# ping ipv6 2001:db8:1::2
3. View IPv6 routes:
R1# show ipv6 route
✅ Key Exam Takeaways
- IPv6 Unicast = one-to-one communication.
- Global Unicast (2000::/3): Internet communication, public.
- Unique Local (FD00::/8): Private internal networks.
- Link-Local (FE80::/10): Local network only, automatic, essential for neighbor communication.
- Every IPv6 interface must have a Link-Local address.
- Global and Unique Local can be added manually or via DHCPv6.
- Always recognize address types by their prefix.
