Westermo RedFox Series - Manual (Page 604)

Westermo OS Management Guide
Version 4.17.0-0
its subnets in the OSPF domain (10.0.1.0/24, 10.0.2.0/24, etc.). From the example
we can also see that the ”network” declaration contains an area parameter.
OSPF areas are further explained in
section 27.1.1.2 .
27.1.1.2 OSPF hierarchy and areas
Being a link state protocol, OSPF requires routers to keep a lot of routing informa-
tion in their database:
❼ Each OSPF router will typically keep a database with information of every
router and link in the whole OSPF domain.
❼ OSPF routers will also redistribute and keep routing information learnt from
external sources (static routes, routes learnt via other routing protocols,
etc.).
To reduce the burden of keeping keeping state information about the whole OSPF
domain, the domain can be split into OSPF areas. (For information on how to
avoid the need to keep information on external routing information, see
sec-
tion 27.1.1.4 .)
Area 0.0.0.2
Area 0.0.0.1
(Backbone area)
Area 0.0.0.0
Area 0.0.0.3
ABR ABR
ABR ABR
R
R
R
R
R
R
R
R R
R
Figure 27.3: Sample OSPF hierarchy with a backbone area and three other areas.
The routers in fig. 27.3 have been divided into four areas. When splitting the
network into multiple areas, each router will only have full knowledge of the
topology within their respective area. Routers will also keep summary information
about destinations outside their own area, but routers will not have knowledge
about the actual topology inside other areas.
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