HP VPN Firewall Appliances Appendix Protocol Reference

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Figure 7 NSSA area
Router types
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 an ABR.
Figure 8 OSPF router types
Route types
OSPF prioritizes routes into the following levels:
• Intra-area route
Area 1
Area 2
Area 3
Area 4
Backbone router
ASBR
IS-IS
RIP
Internal router
ABR
Area 0