IPv6 address types
Global unicast, unique-local and link-local addresses, anycast and multicast groups, and modified EUI-64 interface identifiers.
Unicast scopes
IPv6 unicast scopes and special addresses
| Type | Prefix | Behavior |
|---|---|---|
| Global unicast | 2000::/3 (currently 2000::–3fff::) | Routable on the internet, like public IPv4 |
| Unique local (ULA) | fc00::/7 (fd00::/8 in practice) | Private local scope — like RFC 1918 space; not a deprecated scope and not routed on the internet |
| Link-local | fe80::/10 | Mandatory on every IPv6 interface; valid only on the local link, never routed |
| Loopback | ::1 | Host only |
| Unspecified | :: | Source before the host has an address (e.g., during DAD) |
Link-local appears in every show ipv6 interface and is used for next hops, RA and ND — learn to read it.
Anycast and multicast
Anycast assigns the same address to multiple devices; routing delivers packets to the *nearest* instance — nearest in routing-metric terms, not physical distance. There is no reserved anycast range — any unicast address can be deployed as anycast. Use cases: a shared DNS resolver address or the subnet-router anycast address (all-zeros interface ID).
Common IPv6 multicast groups (ff00::/8)
| Address | Reaches | Seen in |
|---|---|---|
| ff02::1 | All nodes on the link | Neighbor discovery |
| ff02::2 | All routers on the link | Router solicitations |
| ff02::5 | All OSPF routers | OSPFv3 |
| ff02::6 | OSPF DRs | OSPFv3 DR traffic |
| ff02::a | All EIGRPv6 routers | EIGRP for IPv6 |
| ff02::1:ffXX:XXXX | Solicited-node (per unicast address) | NS/DAD — maps the low 24 bits of the target |
Modified EUI-64
Modified EUI-64 builds a 64-bit interface ID from a 48-bit MAC: split the MAC in half, insert fffe in the middle, and flip the 7th bit (the universal/local bit) of the first byte. Hosts and routers can use it for SLAAC or eui-64 addressing.
- MAC
- 00:1a:2b:3c:4d:5e
- Split the MAC:
001a:2b|3c4d:5e. - Insert fffe:
001a:2bff:fe3c:4d5e. - Flip the 7th bit of the first byte: 0x00 → 0x02.
- Result:
021a:2bff:fe3c:4d5e→ interface ID21a:2bff:fe3c:4d5e.
The interface ID is 021a:2bff:fe3c:4d5e — note the flipped bit changes the leading byte.
Recognition and mistakes
Recognize addresses at a glance
- fe80::* → link-local — normal on every interface.
- ff02::* → link-scope multicast — normal in neighbor output.
- fd00::/8 → unique local — valid internally, never on the internet.
- 2000::/3 → global unicast — the 'real' internet address.
Common mistakes
- Treating fe80:: as a misconfiguration — link-local is required and automatic.
- Expecting a broadcast address — IPv6 uses multicast (ff02::1) instead.
- Forgetting the U/L bit flip in EUI-64 — the first byte changes (usually +2).
- Assuming anycast has a dedicated prefix like multicast — it is an addressing *use*, not a range.
Observation: Host has 2001:db8::10 but cannot be reached from another subnet.
- Only link-local connectivity works — global route missing upstream
- Wrong prefix length on the interface
- Using ULA where global was expected
| Check | Indicates |
|---|---|
show ipv6 interface | Confirms the address, scope and /64 prefix actually applied. |
| Ping the link-local address with the interface qualifier | fe80:: reachability isolates a global-routing problem. |
| Router's IPv6 routing table | Missing or wrong prefix entry explains no delivery. |
Correction: Fix the prefix or routing advertisement; keep ULA out of internet-facing paths.
Global unicast ping works across routers; show ipv6 route shows the prefix.
Related resources
Sources
- Cisco CCNA 200-301 v1.1 Exam Topics (official PDF) — reviewed 2026-11-02
- RFC 4291 — IP Version 6 Addressing Architecture — reviewed 2026-11-02
- RFC 4193 — Unique Local IPv6 Unicast Addresses — reviewed 2026-11-02
Targets CCNA 200-301 v1.1 objectives. Supplemental blocks are labeled beyond exam scope.