H3C Technologies H3C S12500 Series Switches - Manual (Page 76)

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Router types
Router classification
OSPF classifies routers into the following types based on their positions in the AS:
• Internal router—All interfaces on an internal router belong to one OSPF area.
• Area Border Router (ABR)—Belongs to more than two areas, one of which must be the backbone
area. An ABR connects the backbone area to a non-backbone area. An ABR and the backbone
area can be connected through a physical or logical link.
• Backbone router—At least one interface of a backbone router must reside in the backbone area.
All ABRs and internal routers in area 0 are backbone routers.
• Autonomous System Boundary Router (ASBR)—Exchanges routing information with another AS. An
ASBR might not reside on the border of the AS. It can be an internal router or ABR.
Figure 22 OSPF router types
Route types
OSPF prioritizes routes into the following levels:
• Intra-area route
• Inter-area route
• Type-1 external route
• Type-2 external route
The intra-area and inter-area routes describe the network topology of the AS. The external routes describe
routes to external ASs.
OSPF classifies external routes into the following types: Type-1 and Type-2. A Type-1 external route has
high credibility. The cost from a router to the destination of the Type-1 external route = the cost from the
router to the corresponding ASBR+ the cost from the ASBR to the destination of the external route.