Célja, hogy összekösse a több OSPF-területekből álló hálózatot.
Konfigurálása megegyezik az egyterületűvel (hálózat címe + wildcard mask
+ area -szám-), de figyeljünk a területek közötti értékekre, azok megfelelő
beállítására. A fenti példa alapján:

R1(config)# router ospf 1
R1(config-router)# router-id 1.1.1.1
R1(config-router)# network 10.1.1.0 0.0.0.255 area 1
R1(config-router)# network 10.1.2.0 0.0.0.255 area 1
R1(config-router)# network 192.168.10.0 0.0.0.3 area 0
R2(config)# router ospf 1
R2(config-router)# router-id 2.2.2.2
R2(config-router)# network 10.2.1.0 0.0.0.255 area 0
R2(config-router)# network 192.168.10.0 0.0.0.3 area 0
R2(config-router)# network 192.168.10.4 0.0.0.3 area 0
R3(config)# router ospf 1
R3(config-router)# router-id 3.3.3.3
R3(config-router)# network 192.168.2.0 0.0.0.255 area 2
R3(config-router)# network 192.168.1.0 0.0.0.255 area 2
R3(config-router)# network 192.168.10.4 0.0.0.3 area 0

LSA | Link State Advertisement

Típusai:
- LSA Type 1 (Router LSA) packets are sent between routers within the same
area of origin and do not leave the area.
- LSA Type 2 (Network LSA) packets are generated by the Designated Router
(DR) to describe all routers connected to its segment directly.

- LSA Type 3 (Summary LSA) packets are generated by Area Border Routers
(ABR) to summarize its directly connected area, and advertise inter-area router
information to other areas the ABR is connected to, with the use of a summary
prefix (e.g 192.168.0.0/22)
- LSA Type 4 (ASBR Summary LSA) packets are the LSAs that advertise the
presence of an Autonomous System Border Router (ASBR) to other areas
- LSA Type 5 (ASBR External LSA) packets are generated by the ASBR to
advertise external redistributed routes into the OSPF’s AS
- LSA Type 6 (Group Membership LSA) packets were designed for Multicast
OSPF (MOSPF), a protocol that supports multicast routing through OSPF.
- LSA Type 7 (NSSA External LSA) packets are used for some special area types
that do not allow external distributed routes to go through and thus block LSA
Type 5 packets from flooding through them, LSA Type 7 packets act as a mask for
LSA Type 5 packets to allow them to move through these special areas and reach
the ABR that is able to translate LSA Type 7 packets back to LSA Type 5 packets.
- LSA Type 8 packets (External Attributes LSA -OSPFv2-/ Link Local LSA -
OSPFv3-) in OSPFv2 (IPv4) are called External Attribute LSAs, and are used to
transit BGP attributes through an OSPF network while BGP destinations are
conveyed via LSA Type 5 packets, however, this feature isn’t supported by most
routers.
- LSA Type 9 in OSPFv2 (IPv4) is defined as a Link Scope Opaque LSA for
carrying OSPF information. For OSPFv3 it’s redefined to handle a communication
prefix for a special area type called Stub Area.
- LSA Type 10 packets are used to flood OSPF information through other area
routers even if these routers do not process this information in order to extend
OSPF functionality, this LSA is used for traffic engineering to advertise MPLS and
other protocols.
- LSA Type 11 packets serve the same purpose as LSA Type 10 packets but are
not flooded into special area types (Stub areas).

OSPF routerek 4 típusa:
- Belső forgalomirányító
- Gerinchálózati forgalomirányító
- Határ-forgalomirányító
- Autonóm rendszer határ-forgalomirányítója (ASBR) -> külső útválasztási
tartományok összekapcsolására szolgál

ABR -> Area Border Router -> a területek szélén lévő, másik területhez
csatlakozó routerek