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IPv6 interface config is simpler than IPv4 — one command per address, no `ip address <ip> <mask>` split. The tricky parts are remembering `ipv6 unicast-routing` and understanding that a link-local address always exists whether you configure one or not.
Router1(config)# ipv6 unicast-routingRouter1(config)# interface gigabitEthernet0/0Router1(config-if)# ipv6 address 2001:db8:acad:1::1/64Router1(config-if)# ipv6 address fe80::1 link-localRouter1(config-if)# no shutdownRouter1(config-if)# end
`ipv6 enable` is useful when you want IPv6 to work on an interface but only need the auto-generated link-local — common on interfaces used for routing adjacencies where global addressing isn't required.
Both interfaces show a link-local (FE80::) and a global unicast (2001:DB8:). If only the FE80 address is showing, `ipv6 unicast-routing` might be missing, or the address line failed (usually a syntax issue — check for stray `::` compressions).
| Symptom | Cause | Fix |
|---|---|---|
| Only FE80:: address shows | `ipv6 unicast-routing` disabled globally | Enable with `ipv6 unicast-routing` |
| Interface has no IPv6 addresses at all | IPv6 disabled on interface | Add `ipv6 enable` or configure an address |
| Address shows but marked tentative | Duplicate Address Detection (DAD) in progress | Wait a few seconds; check for actual duplicate |
| Cannot ping peer on same link | Different link-local subnets, or wrong prefix | Verify /64 on both, check link-local manually |
| Router won't forward packets | No `ipv6 unicast-routing` | Enable globally |
When IPv6 configures an address, it runs Duplicate Address Detection first — sends a neighbor solicitation to make sure no one else has that address, waits for a response window, and only then marks the address preferred. During the wait, the address shows as `tentative` and won't be used.
The `[TEN]` marker means tentative. It'll clear in a couple of seconds unless there's a duplicate address on the link — in which case the address stays tentative and the log shows a duplicate address detection failure.
You configure `ipv6 address 2001:db8:acad:1::1/64` on Gi0/0. The interface is up. `show ipv6 interface brief` shows only FE80::1 — no global address. Ping to a peer fails. What's wrong?
Select the safest next action.
Finish the lesson once you have worked through the material. This awards ★ 35 XP.