Information Technology Reference
In-Depth Information
New link LSA:
For loc al-link flooding scope.
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New intra-area-prefix LSA:
Carries all the IPv6 prefix information. Similar to
OSPFv2 router and network LSAs.
■
Identifying neighbors by router ID:
Neighbors are
always
identified by the router
ID. This does not occur in OSPFv2 point-to-point and broadcast networks.
■
Options field changes:
Two Options bits, the R-bit and the V6-bit, have been added
to the Options field for processing router LSAs during the SPF calculation.
■
Note:
In OSPFv3, the router IDs, area IDs, and LSA link-state IDs remain at the size of 32
bits. Larger IPv6 addresses cannot be used.
OSPFv3 Areas and Router Types
OSPFv3 retains the same structure and concepts as OSPFv2. The area topology, interfaces,
neighbors, link-state database, and routing table remain the same. RFC 2740 does not de-
fine new area types or router types.
The OSPF areas shown in Figure 11-2 and the router types shown in Figure 11-3 remain
the same. The router types in relation to the OSPF areas are
Internal router:
Any router whose interfaces all belong to the same OSPF area.
These routers keep only one link-state database.
■
ABR:
Routers that are connected to more than one area, in which one area is Area 0.
These routers maintain a link-state database for each area they belong to. These
routers generate summary LSAs.
■
ASBR:
Routers that inject external LSAs into the OSPF database (redistribution).
These external routes are learned via either other routing protocols or static routes.
■
Backbone router:
Routers with at least one interface attached to Area 0.
■
OSPFv3 LSAs
OSPFv3 retains the LSA types used by OSPFv2 with some modifications and introduces
two new LSAs: link LSA and intra-area-prefix.
All LSAs use a common 20-byte header that indicates the LS type, the advertising router,
and the sequence number. Figure 11-7 shows the format of the LSA header.
The LS Age indicates the time in seconds since the LSA was generated.
The LS Type indicates the function performed by this LSA. This field includes a U bit and
S2 and S1 bits. When the U bit is set to 0, the LSA is flooded only locally. When the U bit
is set to 1, the LSA is stored and flooded. The S1 and S2 bits have the functions indicated
in Table 11-5.
