3Com CoreBuilder 3500, Implementation Manual

Page: 387 / 592

Link State Databases 387
Link State
Databases
OSPF routers use the information that is contained in the link state
advertisements (LSAs) to build and maintain link state databases. Each
link state database contains the link state advertisements from
throughout the areas to which the router is attached. OSPF uses the
following types of LSAs:
■
Router Link State Advertisements
■
Network Link State Advertisements
■
Summary Link State Advertisements
■
External Link State Advertisements
Router Link State
Advertisements
All routers in an OSPF area originate router link state advertisements, also
known as link state advertisements. Each link state advertisement
describes the state and cost of the originating router’s links (interfaces) to
the area. Information contained in each link state advertisement includes:
■
LSID (Link State ID) — The ID of the router that generated the LSA.
■
Router ID — ID of the router that originated the LSA.
■
LS Seq (Link State Sequence)
— The sequence number of the
advertisement. Used to detect old or duplicate link state
advertisements.
■
LS age — The time, in seconds, since the LSA was generated.
■
Flags
— Possible values:
■
V — Router is the endpoint of an active virtual link that is using the
area as a transit area.
■
ASBR — Router is an autonomous system boundary router (ASBR).
■
ABR — Router is an area border router (ABR).
■
Link Type
— A description of the router link. Possible values:
■
PTP — Connection is point-to-point to another router.
■
Transit — Connection is to a transit network.
■
Stub — Connection to a stub network.
■
Virtual link — Connection is to a far-end router that is the
endpoint of a virtual link.