Ospf Asbrs - Avaya 8800 Configuration Manual

OSPF and RIP fundamentals
Figure 15: Virtual link between ABRs through a transit area
To configure a virtual link between the ABRs in area 1 and area 3, define area 2 as the transit
area between the other two areas, and identify R2 as the neighbor router through which R2
must send information to reach the backbone through R1.

OSPF ASBRs

ASBRs advertise nonOSPF routes into OSPF domains so that they can pass through the OSPF
routing domain. A router can function as an ASBR if one or more interfaces connects to a
nonOSPF network (for example, RIP, BGP, or EGP).
An ASBR imports external routes into the OSPF domain by using ASE LSAs (LSA type 5)
originated by the ASBR.
ASE LSAs flood across area borders. When an ASBR imports external routes, it imports OSPF
route information using external type 1 or type 2 metrics. The result is a four-level routing
hierarchy, as shown in the following table, according to routing preference.
Table 7: ASBR routing hierarchy
Level
1
2
3
4
50 Configuration — OSPF and RIP
Intra-area routing
Inter-area routing
External type 1 metrics
External type 2 metrics
Description
June 2011