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DES-7200 Configuration Guide Chapter 5 OSPF
Configuration
5-2
Each device generates this type of LSAs by itself. They describe the states of its
links in specified areas and the cost spent on reaching the links.In contrast to the
OSPFv2, the Router-LSAs of the OSPFv3 only indicate the state information of
links. They do not record the information about the network addresses connected
to routers. The information will be acquired by newly added types of LSAs.
Additionaly, in the OSPFv2, only one Router-LSA is allowed to be generated for
each device in each area. While in the OSPFv3, multiple Router-LSAs are
allowed to be generated. Thus, when performing the SPF calculation, we must
consider all the Router-LSAs generated by the device. Router-LSAs and
Network-LSAs describe the link topology of areas together.
Caution
Through the flag bits on Router-LSAs, we can know whether the routers are
Area Border Routers (ABR), AS boundary routers (ASBR) or those at one end
of a virtual link.
Network-LSAs (Type 2)
Network-LSAs only exist in broadcast networks or NBMA networks and are
generated by DRs (Designated Routers) in a network. They describe the
information about all the routers connected in specified areas on a network. Like
Router-LSAs, Network-LSAs also only indicate link-state information and do not
record network address information. Network-LSAs and Router-LSAs describe
the link topology of areas together.
Inter-Area-Prefix-LSAs (Type 3)
Generated for an area by the ABRs in the area and used to describe the network
information about reaching other areas. They replace type 3 summary-LSAs in
OSPFv2. In contrast to the OSPFv2, they use a prefix structure to describe
destination network information.
Inter-Area-Router-LSAs (Type 4)
Generated for an area by the ABRs in the area, used to describe the path
information about reaching the ASBRs in other areas, and replacing type 4
summary-LSAs in the OSPFv2.
AS-external-LSAs (Type 5)
This type of LSAs are generated by ASBRs and used to describe the network
information about reaching outside AS. Usually, the network information is
generated through other route protocols. In contrast to the OSPFv2, it uses a
prefix structure to describe destination network information.
NSSA-LSA (Type 7)
Their function is same to that of type 5 AS-external-LSAs. However, they are
generated by ASBRs in the NSSA area.