IP Routing Features
Configuring OSPF
Stub Area
This area connects to the AS backbone through one or more ABRs. It does not
allow an internal ASBR, and does not allow external (type 5) LSAs. A stub area
supports these actions:
■ Advertise the area’s summary routes to the backbone area.
■ Advertise summary routes from other areas.
■ Use the default summary (type-3) route to advertise both of the following:
• summary routes to other areas in the AS
• external routes to other autonomous systems
You can configure the stub area ABR to do the following:
■ Suppress advertising some or all of the area’s summarized internal routes
into the backbone area.
■ Suppress LSA traffic from other areas in the AS by replacing type-3
summary LSAs and the default external route from the backbone area with
the default summary route (0.0.0.0/0).
Virtual links are not allowed for stub areas.
OSPF RFC Compliance
The OSFP features covered in this guide comply with the following:
■ RFC 2328 OSPF version 2
■ RFC 3101 OSPF NSSA option (s/w release K.12.xx and greater)
■ RFC 1583 (Enabled in the default OSPF configuration. Refer to the
following Note.)
Note If all of the routers in your OSPF domain support RFC 2178, RFC 2328, or later,
you should disable RFC 1583 compatibility on all routers in the domain. Refer
to “3. Changing the RFC 1583 OSPF Compliance Setting” on page 5-63.
t
Reducing AS External LSAs and Type-3 Summary LSAs
An OSPF ASBR uses AS External LSAs to originate advertisements of a route
to another routing domain, such as a RIP domain. These advertisements are
■ flooded in the area in which the ASBR operates
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