IP & Routing
IPv6 Addressing
IPv6 uses 128-bit hexadecimal addresses with distinct unicast, multicast, and anycast types. CCNA candidates must recognize address formats and configure them on interfaces.
What you need to know
- Global unicast addresses are publicly routable, typically starting with 2000::/3.
- Link-local addresses use FE80::/10 and are required on every IPv6-enabled interface.
- Unique local addresses (ULA) use FC00::/7, similar in purpose to RFC 1918 private addresses.
- Multicast addresses start with FF00::/8; there is no broadcast in IPv6.
- EUI-64 builds the interface ID from the 48-bit MAC by inserting FFFE and flipping the 7th bit of the first byte.
- Double colon (::) compresses one contiguous run of zeros, usable only once per address.
- Well-known multicast groups: FF02::1 (all nodes), FF02::2 (all routers) on the link-local scope.
Configuration commands
| Command | Mode | Purpose |
|---|---|---|
| ipv6 unicast-routing | config | Enables IPv6 routing globally on the device. |
| interface gigabitethernet0/0 | config | Enters interface configuration mode. |
| ipv6 address 2001:db8:acad:1::1/64 | config-if | Assigns a static global unicast IPv6 address. |
| ipv6 address fe80::1 link-local | config-if | Assigns a specific link-local address instead of the auto-generated one. |
| ipv6 address 2001:db8:acad:1::/64 eui-64 | config-if | Assigns a global address using EUI-64 to build the interface ID. |
| ipv6 enable | config-if | Enables IPv6 processing on an interface without assigning a global address. |
| no shutdown | config-if | Activates the interface. |
Verify it
- show ipv6 interface brief
- show ipv6 interface gigabitethernet0/0
- show ipv6 route
- show running-config | section ipv6
- ping ipv6 2001:db8:acad:1::1
Common mistakes
- Forgetting the global ipv6 unicast-routing command, leaving the router in host mode.
- Confusing the prefix length notation; using /64 for a link with only two addressable hosts intended.
- Assuming a link-local address alone provides end-to-end reachability beyond the local link.
- Typing the compressed form incorrectly with two double colons in one address.
- Forgetting no shutdown after configuring the address, leaving the interface administratively down.
Practise IPv6 Addressing in a real CLI
Generated labs, graded against the simulated network state.