H3C S7500E Series Ethernet Switches Operation Manual

Operation Manual – IPv4 Routing
H3C S7500E Series Ethernet Switches Chapter 3 OSPF Configuration
3-5
Area 0
Area 1
Area 2
Area 3
Area 4
Figure 3-1 OSPF area partition
After area partition, area border routers perform route summarization to reduce the
number of LSAs advertised to other areas and minimize the effect of topology changes.
II. Classification of Routers
The OSPF routers fall into four types according to the position in the AS:
1) Internal Router
All interfaces on an internal router belong to one OSPF area.
2) Area Border Router (ABR)
An area border router belongs to more than two areas, one of which must be the
backbone area. It connects the backbone area to a non-backbone area. The
connection between an area border router and the backbone area can be physical or
logical.
3) Backbone Router
At least one interface of a backbone router must be attached to the backbone area.
Therefore, all ABRs and internal routers in area 0 are backbone routers.
4) Autonomous System Border Router (ASBR)
The router exchanging routing information with another AS is an ASBR, which may not
reside on the boundary of the AS. It can be an internal router or area border router.