What is the usage of the common OPSF LSA?

Created: Apr 5, 2016 05:09:46Latest reply: Apr 5, 2016 08:38:32 1185 1 0 0

What is the usage of the common OPSF LSA?

  • x
  • convention:

Ravger     Created Apr 5, 2016 08:38:32 Helpful(0) Helpful(0)

Router LSA (type 1):
Each router can generate a Router-LSA for each area it belongs to. The Router-LSA (Type1) describes all of the link status and link cost of the router, and all of the known OSPF peer of the link. Router-LSA only makes flooding for each area it belongs to.
Network LSA (type 2):
Network LSA is generated by a DR. Network LSA describes all of the routers in the multiple access network, which lists all of the routers which are connected the local router, including DR itself.
Network summary LSA (type 3):
Network summary LSA is generated by ASR, and will advertise inter-area routes to OSPF areas except the totally stub area and totally NSSA area.
ASBR summary LSA (type 4):
ASBR Summary LSA is generated by ASR, and is used to advertise the location of ASBR to all the related areas except stub, totally stub, NSSA, totally NSSA and the area to which the ASBR belongs. Why is LSA (type 4) needed here? Because that the field of advertiser is always ASBR when LSA (type5) is in broadcasting, so all of the routers in other areas don’t know the location of the advertiser except the router in local area. And the field of advertiser can automatically change to ABR’s router-id when LSA (type3) is broadcast, so each area knows the location of the advertiser. The field of advertiser can automatically change to ABR’s router-id when LSA (type4) is in broadcasting.
Autonomous system external LSA (type 5):
AS-External-LSA (type5) is generated by ASBR, which describes the route to a destination outside the AS or the default route and is advertised to all OSPF areas.
NSSA EXTERNAL LSA (TYPE 7):
The Type 7 LSA is generated by the ASBR in the NSSA, and is flooded only in the NSSA area. The Type 7 LSA describes the route to a destination outside the AS or the default route. Why is Type 7 LSA needed here? Because that the LSA (type4) and LSA (type5) are filtered in NSSA area, but the route which is generated in local area and the outside route which is learned should not be filtered, so the type7 LSA is defined.
  • x
  • convention:

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