OSPF uses an LSDB (link state database) and fills this with
LSAs (link state advertisement) LSA holds the topology information and LSA is held
in the LSDB. Instead of using 1 LSA packet, OSPF has many different varieties of
LSAs.
Here is the list:
LSA Types
|
Description
|
Type 1
|
Router LSAs
|
Type 2
|
Network LSAs
|
Type 3 or 4
|
Summary LSAs
|
Type 5
|
Autonomous system external LSAs
|
Type 6
|
Multicast OSPF LSAs
|
Type 7
|
Defined for not-so-stubby areas
|
Type 8
|
External attribute LSAs for
Border Gateway Protocol (BGP)
|
Type 9, 10, and 11
|
Opaque LSAs
|
LSA Type 1: Router LSA
Type 1 router LSA is generated by internal routers. You can
identify the “O” routes in the routing table, Type 1 LSA floods within its area
only; does not cross ABR. In the type 1 LSA, you will find a list with all the
directly connected links of this router.
LSA Type 2: Network LSA
The network LSA or Type 2 creates for
each multi-access network. LSA Type 2 is advertised by the DR of the transit
network and floods within its area only, network LSA does not cross ABR. You can identify “0” routes in the routing table. In Type 2 LSA you will find all
the routers that are connected to the multi-access network, the DR, and the
prefix and subnet mask.
LSA Type 3: Summary LSA
The summary LSA is created by the ABR to send
updates from one area to another area. You can identify is “OIA” routes in the routing
table. Summary LSA is used to flood network information subnet in the Origin area and cost but does not topology data.
LSA Type 4: ASBR summary LSA
Type 4 LSA is used to advertise ASBR to all other areas in
the autonomous system. ASBR summary LSA includes the router ID of the ASBR in
the link-state ID field.
LSA Type 5: External LSA
Type 5 LSA External LSA also known as autonomous system
external LSA, AS external LSA created by ASBR for external routes redistributed
into OSPF (LSA 5), external LSAs are advertised and owned by the originating
ASBR. External LSAs flood through the entire autonomous system, and advertising router ID (ASBR) is unchanged throughout the system. Type 4 LSA is
needed to find the ASBR.
LSA-6 Multicast OSPF LSA
Type 6 LSA are used in multicast routing (MOSPF routing
protocol) multicast LSA (Cisco routers do not support)
LSA Type 7: NSSA external
Type 7 LSA is created by ASBR inside an NSSA, instead of a
type 5 LSA. Type 7 LSA flooded only within its area of origin and converted to Type
5 LSA on an ABR toward another area.
·
N1- metric increases as it is passed through the network
·
N2- metric doesn’t increase (default)
LSA Type 8: external attribute LSA
External attribute LSA is created by ASBR during BGP to OSPF
redistribution to preserve BGP attributes of the redistribution network.
LSA Type 9, 10, 11
·
Used in OSPF and BGP inter-networking
Here are the lists of all OSPF labs and theories from CCNA to CCIE.
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