Cisco ASR 9000 Series Routing Configuration Guide

occasion might be if your company makes a new acquisition that includes an OSPF area, or if Area 0 itself
is partitioned.
In the case in which an area cannot be connected to Area 0, you must configure a virtual link between that
area and Area 0. The two endpoints of a virtual link are ABRs, and the virtual link must be configured in both
routers. The common nonbackbone area to which the two routers belong is called a transit area. A virtual link
specifies the transit area and the router ID of the other virtual endpoint (the other ABR).
A virtual link cannot be configured through a stub area or NSSA.
This figure illustrates a virtual link from Area 3 to Area 0.
Figure 18: Virtual Link to Area 0
Passive Interface
Setting an interface as passive disables the sending of routing updates for the neighbors, hence adjacencies
will not be formed in OSPF. However, the particular subnet will continue to be advertised to OSPF neighbors.
Use the passive command in appropriate mode to suppress the sending of OSPF protocol operation on an
interface.
It is recommended to use passive configuration on interfaces that are connecting LAN segments with hosts
to the rest of the network, but are not meant to be transit links between routers.
OSPFv2 Sham Link Support for MPLS VPN
In an MPLS VPN environment, several VPN client sites can be connected in the same OSPF area. If these
sites are connected over a backdoor link (intra-area link) and connected over the VPN backbone, all traffic
passes over the backdoor link instead of over the VPN backbone, because provider edge routers advertise
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
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Implementing OSPF
Passive Interface

Cisco ASR 9000 Series Specifications

General

Brand	Cisco
Model	ASR 9000 Series
Category	Network Router
Language	English