IP & Routing
IPv6 Routing
IPv6 routing supports static routes, RIPng, OSPFv3, and EIGRP for IPv6, alongside address autoconfiguration mechanisms like SLAAC and DHCPv6.
What you need to know
- SLAAC uses router advertisements (RA) from ICMPv6 to autoconfigure addresses without a DHCP server.
- DHCPv6 can be stateless (options only, e.g. DNS) or stateful (assigns the full address) depending on RA flags.
- Static IPv6 routes use the ipv6 route command with a prefix, next-hop, and optional exit interface.
- OSPFv3 is enabled per interface with ipv6 ospf process-id area area-id, unlike OSPFv2's network statement approach.
- The default administrative distance for a static IPv6 route is 1, same as IPv4.
- A floating static route is created by specifying a higher administrative distance value.
- ipv6 unicast-routing is a prerequisite for any dynamic IPv6 routing protocol to function.
Configuration commands
| Command | Mode | Purpose |
|---|---|---|
| ipv6 unicast-routing | config | Enables IPv6 routing on the device. |
| ipv6 route 2001:db8:acad:2::/64 2001:db8:acad:12::2 | config | Configures a static IPv6 route via a next-hop address. |
| ipv6 route ::/0 2001:db8:acad:12::2 | config | Configures a default IPv6 static route. |
| router ospfv3 1 | config | Creates an OSPFv3 routing process. |
| router-id 1.1.1.1 | config-router | Manually sets the OSPFv3 router ID, required since IPv6 interfaces lack IPv4 addresses. |
| interface gigabitethernet0/0 | config | Enters interface configuration mode. |
| ipv6 ospf 1 area 0 | config-if | Enables OSPFv3 on the interface for area 0. |
| ipv6 nd other-config-flag | config-if | Sets the O-flag in RAs, telling hosts to use DHCPv6 for stateless options. |
Verify it
- show ipv6 route
- show ipv6 route static
- show ipv6 ospf neighbor
- show ipv6 ospf interface brief
- show ipv6 protocols
- show ipv6 interface gigabitethernet0/0
Common mistakes
- Forgetting to set a router-id manually on OSPFv3 when no IPv4 address exists on any interface.
- Mixing up ipv6 route next-hop syntax and pointing to a link-local address without specifying the exit interface.
- Not enabling ipv6 unicast-routing before starting a dynamic routing protocol.
- Assuming SLAAC alone provides DNS server information without RDNSS or DHCPv6 stateless.
- Applying ipv6 ospf under the wrong interface or wrong area, causing neighbors to stay down.
Practise IPv6 Routing in a real CLI
Generated labs, graded against the simulated network state.