Default Route For Ospf; Link-State Advertisement Types For Ospf Version 2 - Cisco ASR 9000 Series Configuration Manual

Implementing OSPF

Default Route for OSPF

Type 5 (ASE) LSAs are generated and flooded to all areas except stub areas. For the routers in a stub area to
be able to route packets to destinations outside the stub area, a default route is injected by the ABR attached
to the stub area.
The cost of the default route is 1 (default) or is determined by the value specified in the default-cost command.

Link-State Advertisement Types for OSPF Version 2

Each of the following LSA types has a different purpose:
• Router LSA (Type 1)—Describes the links that the router has within a single area, and the cost of each
• Network LSA (Type 2)—Describes the link state and cost information for all routers attached to a
• Summary LSA for ABRs (Type 3)—Advertises internal networks to routers in other areas (interarea
• Summary LSA for ASBRs (Type 4)—Advertises an ASBR and the cost to reach it. Routers that are
• Autonomous system external LSA (Type 5)—Redistributes routes from another autonomous system,
• Autonomous system external LSA (Type 7)—Provides for carrying external route information within
• Intra-area-prefix LSAs (Type 9)—A router can originate multiple intra-area-prefix LSAs for every router
• Area local scope (Type 10)—Opaque LSAs are not flooded past the borders of their associated area.
• Link-state (Type 11)—The LSA is flooded throughout the AS. The flooding scope of Type 11 LSAs
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link. These LSAs are flooded within an area only. The LSA indicates if the router can compute paths
based on quality of service (QoS), whether it is an ABR or ASBR, and if it is one end of a virtual link.
Type 1 LSAs are also used to advertise stub networks.
multiaccess network segment. This LSA lists all the routers that have interfaces attached to the network
segment. It is the job of the designated router of a network segment to generate and track the contents
of this LSA.
routes). Type 3 LSAs may represent a single network or a set of networks aggregated into one prefix.
Only ABRs generate summary LSAs.
trying to reach an external network use these advertisements to determine the best path to the next hop.
ABRs generate Type 4 LSAs.
usually from a different routing protocol into OSPF.
an NSSA. Type 7 LSAs may be originated by and advertised throughout an NSSA. NSSAs do not receive
or originate Type 5 LSAs. Type 7 LSAs are advertised only within a single NSSA. They are not flooded
into the backbone area or into any other area by border routers.
or transit network, each with a unique link-state ID. The link-state ID for each intra-area-prefix LSA
describes its association to either the router LSA or network LSA and contains prefixes for stub and
transit networks.
are equivalent to the flooding scope of AS-external (Type 5) LSAs. Similar to Type 5 LSAs, the LSA
is rejected if a Type 11 opaque LSA is received in a stub area from a neighboring router within the stub
area. Type 11 opaque LSAs have these attributes:
◦ LSAs are flooded throughout all transit areas.
◦ LSAs are not flooded into stub areas from the backbone.
◦ LSAs are not originated by routers into their connected stub areas.
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
Default Route for OSPF
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