Alternative Area Border Router (Abr) - HP procurve 8100fl series Management And Configuration Manual

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Alternative Area Border Router (ABR)

The switch automatically supports the alternative ABR implementation, as
defined in the IETF "Alternative OSPF ABR Implementations" Internet
Working Draft. This feature improves the behavior of a router connected to
multiple areas without an active backbone connection. Behavior
modifications allow the alternative ABR to successfully forward routes to the
backbone and other areas despite not being actively connected to the
backbone.
The switch implements the alternative ABR feature automatically. No
configuration changes are necessary.
ProCurve's OSPF implementation considers a router to be an ABR if it satisfies
the following three requirements:
■ One or more non-backbone areas actively attached. As defined in the IETF
working draft, "An area is considered actively attached if the router has
at least one interface in that area in the state other than Down."
Area 0 configured.
■
■ An interface in the Up state in Area 0. This requirement is satisfied even
if the adjacent interface on the Area 0 peer is in the Down state. As long
as the ABR's interface in Area 0 has not been administratively shut down,
it will continue to function as an ABR. A loopback interface belonging to
the backbone will also be considered as an active attachment to the
backbone.
If an ABR that is actively attached to more than one non-backbone area ceases
to satisfy the above Area 0 requirements (configured and an interface in the
Up state), it no longer functions as an ABR, provided that its non-backbone
areas are connected to the backbone themselves.
For meaningful routing to occur, the areas to which the Alternative ABR
connects, must themselves be connected to the backbone. As the IETF draft
reiterates, "[This feature does] not obviate the need of virtual link
configuration in case an area has no physical backbone connection at all. The
methods described here improve the behavior of a router connecting two or
more backbone-attached areas."
OSPF Configuration

Alternative Area Border Router (ABR)

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