What this note covers
OSPFv3 is the version of OSPF built for IPv6. It keeps the
same core mechanics as OSPFv2 but changes how addressing is handled,
adds two new LSA types, and renames a few others. Know the
differences — the fundamentals you already learned still apply.
Generalities
Key facts
- Originally created to support IPv6; later extended to also
carry IPv4 (address-family support).- Same core operation as OSPFv2: SPF algorithm, areas, DR/BDR,
flooding, timers, the neighbor state machine.- Runs over IPv6.
- Can advertise all logical networks on an interface (IPv6),
rather than being tied to a single subnet per interface.- Uses IPsec (native to IPv6) for authentication, instead of
OSPFv2’s built-in authentication schemes.- Defined in RFC 5340.
What changed in addressing
LSAs decoupled from IP addressing
In OSPFv3, the Type 1 and Type 2 LSAs no longer carry IP address
information. Topology (who connects to whom) is separated from
addressing (what prefixes live there). Prefixes are carried by the
new LSA types instead — this is the biggest structural change from
OSPFv2.
New LSA types in OSPFv3
Two additions
- Type 8 — Link LSA: carries the router’s link-local address
and the IPv6 prefixes on a link; has link-local scope (stays on
the one link).- Type 9 — Intra-Area Prefix LSA: carries IPv6 prefixes
associated with a router or a transit segment, within the area.
The 8/9 numbering clash with OSPFv2
In OSPFv2, LSA numbers 8–11 are opaque LSAs (used for
extensions like MPLS-TE — see 06 - LSA Types & the LSDB). In
OSPFv3, 8 and 9 mean the Link LSA and Intra-Area Prefix
LSA. Same numbers, different meaning depending on the version —
don’t mix them up.
Multicast addresses
IPv6 equivalents
The OSPFv2 addresses map to IPv6 multicast:
- FF02::5 — AllSPFRouters (equivalent of 224.0.0.5).
- FF02::6 — AllDRouters (equivalent of 224.0.0.6).
OSPFv2 → OSPFv3 naming
What got renamed
OSPFv2 OSPFv3 Summary LSA (Type 3) Inter-Area Prefix LSA ASBR Summary LSA (Type 4) Inter-Area Router LSA NSSA External (Type 7) Type 7 LSA (unchanged in role) The function is the same as the OSPFv2 equivalents you already
know — the names were updated to describe what they carry.
The one-line takeaway
How to think about OSPFv3
It’s OSPF you already understand, adapted for IPv6: same SPF, same
areas, same DR/BDR, same states. The differences are addressing
pulled out of Types 1/2, two new prefix-carrying LSAs (8/9),
IPsec instead of built-in auth, and FF02::5 / FF02::6 for
multicast.