Multipath Support; Ospf Areas - HP procurve 8100fl series Management And Configuration Manual

Multipath Support

The 8100fl switch supports OSPF and static Multi-path. If multiple equal-cost
OSPF or static routes have been defined for any destination, then the switch
"discovers" and uses all of them. The switch will automatically learn up to
sixteen equal-cost OSPF or static routes and retain them in its forwarding
information base (FIB). The forwarding module then installs flows for these
destinations in a round-robin fashion.

OSPF Areas

OSPF areas are a collection of subnets that are grouped in a logical fashion.
Each area maintains its own link state database. The area topology is known
only within the area. A router maintains a separate link state database for each
area to which it is connected.
The goal of forming areas is to limit the number of routers that need to directly
exchange routing information with each other, and to permit summarization
of routing information on area boundaries. It is the link state nature of the
protocol, combined with its ability to support hierarchy via areas, that results
in significantly higher scalability than Distance Vector routing protocols, such
as RIP.
There are several types of OSPF Areas supported by the ProCurve 8100fl,
which differ in the way they handle External routes.
Backbone (area 0): The backbone is responsible for distributing routing
■
information between non-backbone areas. OSPF areas communicate with
other areas via the backbone area. The OSPF area backbone contains all
Area Border Routers (ABRs).
■ Normal: Normal areas can have Stubs in them, which redistribute
externals into the area. Such Externals will be passed through the ABR
which connects this area to the Backbone. Externals originated in other
areas will also be injected into the Normal area via the ABR.
Stub: An ASBR (Autonomous System Border Router) cannot be placed in
■
a Stub area, and therefore no Externals can be injected in it. An ABR that
connects a Stub area to the Backbone will propagate into the Stub area
only a default route, accompanied by an Inter-area route.
■ NSSA (Not So Stubby Area): Defined in RFC 1587, NSSAs can have ASBRs
in them, therefore Externals can be injected into NSSAs. Those externals
are propagated by the ASB towards the backbone. Externals injected into
other areas are NOT propagated into the NSSA. In summary, the NSSA
handles Externals as a Normal area in the direction from the NSSA to the
Backbone, and as a Stub Area in the direction of the Backbone to the
NSSA.
OSPF Configuration
Overview
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