3com 3031 Instruccion De Instalación
OSPF Overview
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and bandwidth utility of the network is accordingly reduced. Besides, each change
in topology structure requires all routers in the network to rerun route calculation.
in topology structure requires all routers in the network to rerun route calculation.
To solve this problem, OSPF splits an AS into multiple areas, which are identified by
area IDs. In logical sense, the areas put routers into different groups. The area 0,
also known as backbone area, is of the most significance.
area IDs. In logical sense, the areas put routers into different groups. The area 0,
also known as backbone area, is of the most significance.
The backbone area achieves routing information exchange between the
non-backbone areas. The backbone area and other non-backbone areas must be
physically consecutive. Otherwise, you have to configure virtual links to make
them consective.
non-backbone areas. The backbone area and other non-backbone areas must be
physically consecutive. Otherwise, you have to configure virtual links to make
them consective.
The router connecting the backbone area and another area is called area border
router (ABR).
router (ABR).
There also exists the autonomous system boudndard router (ASBR) in OSPF, which
connects OSPF routing domain and the router running other routing protocols can
be taken as the router importing OSPF external roting information.
connects OSPF routing domain and the router running other routing protocols can
be taken as the router importing OSPF external roting information.
Route aggregation
AS is divided into different areas, which are interconnected via OSPF ABRs. The
routing information between areas can be reduced through route aggregation.
Thus, the size of routing table can be reduced and the calculation speed of the
router can be improved.
routing information between areas can be reduced through route aggregation.
Thus, the size of routing table can be reduced and the calculation speed of the
router can be improved.
After calculating an intra-area route of an area, the ABR will look up the routing
table and encapsulate each OSPF route into an LSA and send it outside the area.
table and encapsulate each OSPF route into an LSA and send it outside the area.
For example, in Figure 126, there are three intra-area routes in Area 19,
19.1.1.0/24, 19.1.2.0/24 and 19.1.3.0/24. If route aggregation is configured and
the three routes are aggregated into one route 19.1.0.0/16, only one LSA, which
describes the route after aggregation, is generated on RTA.
19.1.1.0/24, 19.1.2.0/24 and 19.1.3.0/24. If route aggregation is configured and
the three routes are aggregated into one route 19.1.0.0/16, only one LSA, which
describes the route after aggregation, is generated on RTA.
Figure 126 Area and route aggregation
OSPF Packets
OSPF uses five types of packets:
■
Hello Packet:
Area 12
Area 8
Area 19
Area 0
Virtual Link
19.1.1.0/24
19.1.2.0/24
19.1.3.0/24
RTA