Brocade Communications Systems ICX 7250 series, Configuration Manual

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OSPFv3 areas
After OSPFv3 is enabled, you can assign OSPFv3 areas. You can assign an IPv6 address or a number as the area ID for each area. The
area ID is representative of all IP addresses (subnets) on a device interface. Each device interface can support one area.
NOTE
You can assign only one area on a device interface.
NOTE
You are required to configure a router ID when running only IPv6 routing
protocols.
Backbone area
The backbone area (also known as area 0 or area 0.0.0.0) forms the core of OSPFv2 and OSPFv3 networks. All other areas are
connected to it, and inter-area routing happens by way of routers connected to the backbone area and to their own associated areas.
The backbone area is the logical and physical structure for the OSPF domain and is attached to all non-zero areas in the OSPF domain.
The backbone area is responsible for distributing routing information between non-backbone areas. The backbone must be contiguous,
but it does not need to be physically contiguous; backbone connectivity can be established and maintained through the configuration of
virtual links.
Area types
OSPFv3 areas can be normal, a stub area, a totally stubby area (TSA), or a not-so-stubby area (NSSA).
• Normal: OSPFv3 devices within a normal area can send and receive external link-state advertisements (LSAs).
• Stub: OSPFv3 devices within a stub area cannot send or receive External LSAs. In addition, OSPF devices in a stub area must
use a default route to the area’s Area Border Router (ABR) to send traffic out of the area.
• TSA: Similar to a stub area, a TSA does not allow summary routes in addition to not having external routes.
• NSSA: The Autonomous System Boundary Router (ASBR) of an NSSA can import external route information into the area.
–
ASBRs redistribute (import) external routes into the NSSA as type 7 LSAs. Type 7 External LSAs are a special type of LSA
generated only by ASBRs within an NSSA, and are flooded to all the routers within only that NSSA.
– ABRs translate type 7 LSAs into type 5 External LSAs, which can then be flooded throughout the autonomous system.
The NSSA translator converts a type 7 LSA to a type 5 LSA if F-bit and P-bit are set and there is a reachable forwarding
address. An ABR translates to a type 5 only when P-bit is set in the type 7 LSA.
When an NSSA contains more than one ABR, OSPFv3 elects one of the ABRs to perform the LSA translation for NSSA. OSPF elects
the ABR with the highest router ID. If the elected ABR becomes unavailable, OSPFv3 automatically elects the ABR with the next highest
router ID to take over translation of LSAs for the NSSA. The election process for NSSA ABRs is automatic.
OSPFv3 areas
Brocade FastIron Layer 3 Routing Configuration Guide
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