📘 CCNA 200-301 v1.1
1.8 Configure and verify IPv6 addressing and prefix
🔹 1. Introduction to IPv6
IPv6 (Internet Protocol version 6) is the next generation of IP addressing, developed to replace IPv4 because IPv4 addresses are running out.
IPv6 provides a larger address space, improved routing efficiency, and built-in security features.
- IPv4 uses 32 bits per address → about 4.3 billion addresses
- IPv6 uses 128 bits per address → about 340 undecillion addresses (a number so large that we’ll never run out)
🔹 2. IPv6 Address Structure
An IPv6 address is made up of 128 bits, written as eight groups of 16 bits (each group is written as 4 hexadecimal digits) separated by colons (:).
Example:
2001:0db8:0000:0000:0000:ff00:0042:8329
Each hexadecimal digit represents 4 bits →
8 groups × 16 bits = 128 bits total.
🔹 3. IPv6 Address Shortening Rules
To make IPv6 addresses easier to read and write, two rules are used:
Rule 1: Remove leading zeros
Example:
2001:0db8:0000:0000:0000:ff00:0042:8329
↓
2001:db8:0:0:0:ff00:42:8329
Rule 2: Use double colon (::) for consecutive zeros
You can replace one sequence of consecutive groups of zeros with ::
2001:db8:0:0:0:ff00:42:8329
↓
2001:db8::ff00:42:8329
⚠️ Important rule:
You can use :: only once in an address.
🔹 4. Types of IPv6 Addresses
IPv6 has different types of addresses used for different purposes.
1. Unicast Address
- Identifies one single interface.
- Packet sent to a unicast address is delivered to one device.
Types of unicast addresses:
| Type | Prefix | Purpose | Example |
|---|---|---|---|
| Global Unicast | 2000::/3 | Public IPv6 address (similar to public IPv4) | 2001:db8::1 |
| Link-Local | fe80::/10 | Used on local network segment only (no router forwarding) | fe80::1 |
| Unique Local (ULA) | fc00::/7 | Private use within an organization (similar to private IPv4) | fd00::1 |
2. Multicast Address
- Used to send traffic to multiple devices (a group).
- Example: all routers, all nodes, etc.
- Prefix: ff00::/8
Example multicast addresses:
| Group | Address |
|---|---|
| All nodes | ff02::1 |
| All routers | ff02::2 |
3. Anycast Address
- Assigned to multiple interfaces (usually routers).
- Packet goes to the nearest interface (based on routing distance).
Used for redundancy and load balancing.
🔹 5. IPv6 Prefix and Subnetting
IPv6 addresses are divided into two parts:
| Part | Description | Example |
|---|---|---|
| Network prefix | Identifies network or subnet | 2001:db8:abcd::/64 |
| Interface ID | Identifies a specific interface | ::1 |
Example IPv6 address breakdown:
2001:db8:abcd:0012::1/64
- Prefix = 2001:db8:abcd:0012::
- Prefix length = /64 → first 64 bits represent the network
- Interface ID = last 64 bits represent the host (interface)
Typical prefix length:
- /64 is the standard prefix length for most IPv6 LANs.
🔹 6. IPv6 Address Types in Routers and PCs
When a device (like a PC or router) is enabled for IPv6, it usually has multiple IPv6 addresses on an interface:
| Address Type | Description |
|---|---|
| Link-local (FE80::/10) | Automatically assigned, used for local communication |
| Global Unicast | Manually or dynamically assigned for global communication |
| Multicast | Automatically assigned for group communications |
| Anycast | Manually configured if needed |
🔹 7. Methods of IPv6 Address Assignment
IPv6 supports several ways to assign addresses to devices:
1. Manual Configuration (Static IPv6)
Manually assign an IPv6 address to an interface.
Example (on Cisco router):
Router(config)# interface g0/0
Router(config-if)# ipv6 address 2001:db8:abcd:1::1/64
Router(config-if)# no shutdown
To assign a link-local address manually:
Router(config-if)# ipv6 address fe80::1 link-local
2. Stateless Address Autoconfiguration (SLAAC)
Devices automatically generate their own IPv6 address using:
- The prefix advertised by a router, and
- The device’s interface ID (usually derived from MAC address)
Example:
- Router advertises
2001:db8:abcd:1::/64 - Host forms:
2001:db8:abcd:1:xxxx:xxxx:xxxx:xxxx
Command to enable router advertisements:
Router(config-if)# ipv6 unicast-routing
Router(config-if)# interface g0/0
Router(config-if)# ipv6 address 2001:db8:abcd:1::1/64
3. Stateful (DHCPv6)
Similar to DHCP in IPv4.
A DHCPv6 server assigns IPv6 addresses and other information (like DNS, gateway).
Router interface configuration example:
Router(config-if)# ipv6 address dhcp
4. Combination (SLAAC + DHCPv6)
Device uses SLAAC for address, and DHCPv6 for additional info (like DNS server).
🔹 8. Verifying IPv6 Configuration
On Cisco Router or Switch:
Check IPv6 interface configuration:
R1# show ipv6 interface g0/0
It displays:
- IPv6 address
- Link-local address
- Prefix
- Multicast groups
Check IPv6 routing table:
R1# show ipv6 route
Shows learned and connected networks.
Ping test for IPv6:
R1# ping ipv6 2001:db8:abcd:1::2
Traceroute IPv6 path:
R1# traceroute ipv6 2001:db8:abcd:2::1
🔹 9. IPv6 Prefixes (Important for Exam)
| Prefix | Meaning | Description |
|---|---|---|
| /128 | Single interface | One specific device |
| /64 | Typical LAN subnet | Default for most networks |
| /48 | Site-level prefix | Often assigned by ISPs to organizations |
| /32 | Global prefix | Assigned to ISPs |
| /10 | Link-local | FE80::/10 |
| /7 | Unique Local | FC00::/7 |
| /3 | Global Unicast | 2000::/3 |
🔹 10. IPv6 Loopback and Unspecified Address
| Address | Description | Usage |
|---|---|---|
| ::1/128 | Loopback address | Used to test local interface (like 127.0.0.1 in IPv4) |
| ::/128 | Unspecified address | Used as a placeholder when a device doesn’t yet have an IP address (e.g., DHCPv6 request) |
🔹 11. IPv6 Routing (Basic Concept)
Routers can route IPv6 traffic if IPv6 routing is enabled.
Enable it:
Router(config)# ipv6 unicast-routing
To configure static IPv6 routes:
Router(config)# ipv6 route 2001:db8:abcd:2::/64 2001:db8:abcd:1::2
✅ Summary Checklist for CCNA Exam
| Concept | You Must Know |
|---|---|
| IPv6 address structure (128-bit, hex format) | ✔️ |
| Shortening rules (omit zeros, use :: once) | ✔️ |
| Types: unicast, multicast, anycast | ✔️ |
| Address types: global, link-local, unique local | ✔️ |
| IPv6 prefix meaning (/64, /48, etc.) | ✔️ |
| Methods of configuration: static, SLAAC, DHCPv6 | ✔️ |
Verification commands (show ipv6 interface, show ipv6 route) | ✔️ |
| IPv6 routing basic configuration | ✔️ |
