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Configuring the Switch
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3
Displaying Link State Database Information
OSPF routers advertise routes using Link State Advertisements (LSAs). The full
collection of LSAs collected by a router interface from the attached area is known as
a link state database. Routers that are connected to multiple interfaces will have a
separate database for each area. Each router in the same area should have an
identical database describing the topology for that area, and the shortest path to
external destinations.
The full database is exchanged between neighboring routers as soon as a new
router is discovered. Afterwards, any changes that occur in the routing tables are
synchronized with neighboring routers through a process called reliable flooding.
You can show information about different LSAs stored in this router’s database,
which may include any of the following types:
• Router (Type 1) – All routers in an OSPF area originate Router LSAs that describe
the state and cost of its active interfaces and neighbors.
• Network (Type 2) – The designated router for each area originates a Network LSA
that describes all the routers that are attached to this network segment.
• Summary (Type 3) – Area border routers can generate Summary LSAs that give
the cost to a subnetwork located outside the area.
• AS Summary (Type 4) – Area border routers can generate AS Summary LSAs that
give the cost to an autonomous system boundary router (ASBR).
• AS External (Type 5) – An ASBR can generate an AS External LSA for each known
network destination outside the AS.
• NSSA External (Type 7) – An ASBR within an NSSA generates an NSSA external
link state advertisement for each known network destination outside the AS.
Command Attributes
• Area ID – Area defined for which you want to view LSA information.
(This item must be entered in the form of an IP address.)
• Link ID – The network portion described by an LSA. The Link ID should be:
- An IP network number for Type 3 Summary and Type 5 AS External LSAs.
(When an Type 5 AS External LSA is describing a default route, its Link ID
is set to the default destination 0.0.0.0.)
- A Router ID for Router, Network, and Type 4 AS Summary LSAs.
• Self-Originate – Shows LSAs originated by this router.
• LS Type – LSA Type (Options: Type 1-5, 7). See the preceding description.
• Adv Router – IP address of the advertising router. If not entered, information about
all advertising routers is displayed.
• Age
25
– Age of LSA (in seconds).
• Seq
25
– Sequence number of LSA (used to detect older duplicate LSAs).
• CheckSum
25
– Checksum of the complete contents of the LSA.
25. These items are read only.