HP 3500YL - Manual (Page 221)

IP Routing Features
Configuring OSPF
OSPF Router Types
Interior Routers
This type of OSPF router belongs to only one area. Interior routers flood type­
1 LSAs to all routers in the same area, and maintain identical link state
databases (LSDBs). In figure 5-18, below, routers R1, R3, R4, and R6 are all
interior routers because all of their links are to other routers in the same area.
R1
R2 R5
R3
R4 R6
Area 0 (Backbone)
Area 1
Ar
ea
2
Interior Routers
Interior Router
Figure 5-18. Example of Interior Routers
Area Border Routers (ABRs)
This type of OSPF router has membership in multiple areas. ABRs are used to
connect the various areas in an AS to the backbone area for that AS. Multiple
ABRs can be used to connect a given area to the backbone, and a given ABR
can belong to multiple areas other than the backbone. An ABR maintains a
separate LSDB for each area to which it belongs. (All routers within the same
area have identical LSDBs.) The ABR is responsible for flooding summary
LSAs between its border areas. You can reduce summary LSA flooding by
configuring area ranges. An area range enables you to assign an aggregate
address to a range of IP addresses. This aggregate address is advertised
instead of all the individual addresses it represents. You can assign up to eight
ranges in an OSPF area. In figure 5-19, below, routers R2 and R5 are Area
Border Routers (ABRs) because they both have membership in more than one
area.
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