Section B.9. OSPFv3 Messages and the Link State Database (Chapter 8)

B.9. OSPFv3 Messages and the Link State Database (Chapter 8)

Table B-17 lists all possible OSPF for IPv6 packet types.

Table B-17. OSPF for IPv6 packet types

Packet type	Name	Description
1	Hello	Initializes and maintains adjacencies. Also used to elect DR and BDR. See the section "Forming Adjacencies."
2	Database Description	Exchanges database description during the formation of adjacencies. See the section "Forming Adjacencies."
3	Link State Request	Requests missing or changed LSAs. See the section "Forming Adjacencies."
4	Link State Update	Transmits LSAs either responding to requests when forming adjacencies or during LSA flooding. See the sections "Forming Adjacencies" and "LSA Flooding."
5	Link State Acknowledgment	Acknowledges the reception of an LSA. Every LSA must be acknowledged. See the sections "Forming Adjacencies" and "LSA Flooding."

The Options field describes the optional capabilities of the router. Table B-18 explains the bits used in the Options field.

Table B-18. The Options field

Bit	Name	Description
0-17	Not used	Reserved for future use.
18	DC	Handling of Demand Circuits, as described in RFC 1793.
19	R	Indicates that the originator of the Hello packet is an active router. If this bit is set to 0, the originator will not forward packets: for example, a multihomed host that wants to build an OSPF routing table without actually routing packets.
20	N	All routers within an NSSA must set this bit. In addition, the E bit must be set to 0 (see RFC 3101).
21	MC	Multicast capability, as defined in RFC 1584.
22	E	External-routes capability of the router. All members of an area must agree on the external capability. In a stub area, all routers must set this bit to 0 to achieve adjacency. The E bit is meaningful only in Hello packets (similar to the N bit).
23	V6	Indicates that the router supports OSPF for IPv6. If set to 0, this router/link should be excluded from IPv6 routing calculation.

Table B-19 shows possible link state types. The LS type is represented in hexadecimal notation to reflect the flooding scope.

Table B-19. Link state (LS) types

LS type	Name	Flooding scope	Advertised by	Link State ID
0x2001	Router-LSA	Area	Each router	Router ID
0x2002	Network-LSA	Area	DR	DR's Interface ID of the transit link
0x2003	Inter-Area-Prefix-LSA	Area	ABR	A locally unique ID set by ABR
0x2004	Inter-Area-Router-LSA	Area	ABR	A locally unique ID set by ABR
0x4005	AS-External-LSA	AS	ASBR	A locally unique ID set by ASBR
0x2006	Group-Membership-LSA	Area	See RFC 1584	See RFC 1584
0x2007	Type-7-LSA	Area	See RFC 3101	See RFC 3101
0x0008	Link-LSA	Link	Each router for each link	Locally unique Interface ID
0x2009	Intra-Area-Prefix-LSA	Area	Each router	A locally unique ID set by router

The Flags field indicates the special function of the router originating the LSA. Table B-20 shows the possible values and their corresponding functions

Table B-20. Flags in Router-LSA

Bit	Name
W bit	The router is a wildcard multicast receiver. See RFC 1584 for more information.
V bit	The router is the endpoint of a virtual link using this area as a transit area.
E bit	The router is an ASBR.
B bit	The router is an ABR.

The link types shown in Table B-21 describe the possible link types of an interface in a Router-LSA.

Table B-21. Link type supported in a Router-LSA

Link type	Name	Neighbor Interface ID	Neighbor Router ID
1	Point-to-point	Interface ID of the neighbor on the other end of the point-to-point link	Router-ID of the neighbor on the other end of the point-to-point link
2	Transit	Interface ID of the DR on this link	Router ID of the DR on this link
3	Reserved	N/A	N/A
4	Virtual	Interface ID of the neighbor on the other end of the virtual link	Router ID of the neighbor on the other end of the virtual link

Table 2-22 explains the prefix options starting with the leftmost bit in an Inter-Area-Prefix-LSA.

Table 2-22. Prefix options starting with the leftmost bit

Bit	Name	Description
0-3	Reserved	N/A
4	P bit	Propagate bit: if set, the NSSA ABR readvertises the prefix into the backbone. Used only in Type-7-LSA.
5	MC bit	Multicast bit: if set, the prefix should be included in IPv6 multicast routing calculations.
6	LA bit	Local address bit: if set, the prefix is actually a local IPv6 address of the originating router.
7	NU bit	No unicast bit: if set, the prefix should be excluded from IPv6 unicast calculation.