Lsa Types

Front 1

Router LSA
Type 1

Back 1

Describes state and cost of router's interfaces to the area

Router will have 1 for each router in area

V,E,B Bits: V = virtual link, E = ASBR, B = ABR
=> [show ospf database router extensive] -> "bits 0x#"

Link ID describes far side of link
Link Data describes local side of link

Link Type : Link ID : Link Data
PtP : Neighbor's RID : Local int IP
Transit : DR's int IP : local int IP
Stub : Network number : Subnet mask
Virtual Link : Neighbor's RID : Local int IP

Front 2

Network LSA
Type 2

Back 2

Describes all routers attached to a network segment

Sent by DR on link

Front 3

Summary LSA
Type 3

Back 3

Generated by ABRs to describe networks external to the area

Lists network, advertising router's RID, and netmask

Front 4

ASBR Summary
Type 4

Back 4

Generated by ABR to inform adjacent areas about the presence of an ASBR

Front 5

AS External LSA
Type 5

Back 5

Originated by ASBR to describe routes external to OSPF

E bit:
0: Type 2 external metric (default). Local router uses encoded metric as total cost for the route

1: Type 1 external metric. Local router adds cost to reach ASBR to encoded metric

Front 6

NSSA External
Type 7

Back 6

Same as Type 5, used by ASBRs in a NSSA

ABRs translate Type 7s to Type 5s at area border

When multiple ABRs, highest RID advertises Type 5

ABRs that are ASBRs will by default export their external routes in to NSSAs as Type 7s. [no-nssa-abr] will stop it exporting

Front 7

Opaque LSA
Types 9-11

Back 7

Allows for extensibility of OSPF

Type 9: graceful restart, link-local scope

Type 10: MPLS traffic engineering, area scope

Type 11: not supported, domain scope