Table of contents
- Type 1: Router LSA
- Type 2: Network LSA
- Type 3: Inter-Area Prefix LSA
- Type 4: Inter-Area Router LSA
- Type 5: AS-External LSA
- LSA Type 6: Group Membership
- LSA Type 7: NSSA
- Type 8: Link LSA
- Type 9: Intra-Area Prefix LSA
- Opaque LSAs
- Related Lessons
- Related Materials
OSPFv3 Link State Advertisements (LSAs) are used to share network topology information with other routers that share the same OSPF process.
Most OSPFv3 networks only need to use a handful of LSAs. In this lesson, we'll cover all 11 of them:
|10||Area Scope (Opaque)|
Type 1: Router LSA
Type 1: Router LSAs share topology information about itself and its neighbors only to adjacent routers within the same area that share the same OSPFv3 process.
In point-to-point and point-to-multipoint networks, all routers in an area send Router LSAs directly to each other:
In Non-Broadcast Multi-Access (NBMA) networks, all routers in an area send Router LSAs to the Designated Router (and Backup Designated Router if the area has one). This is diagrammed below in the description for Type 2: Network LSA.
Type 2: Network LSA
The DR (designated Router) collects topology information from all routers in its area. The DR then embeds this information into a Network LSA and sends the LSA to all routers within the same area.
Type 3: Inter-Area Prefix LSA
ABRs create and send Inter-Area Prefixes to advertise networks in different areas. Routes learned through these Type 3: Inter-Area Prefix LSAs are listed in the routing table as being learned from O IA (OSPF Inter-Area).
In the diagram above, R-1 generates a Type 1: Router LSA and sends it to R-2.
Since R2 is an ABR, it will take the information learned from the Type 1: Router LSA and add its own network information to it. R-2 will then embed this information into a Type 3: Network LSA and send it to R-3
R3, also being an ABR, will take the information learned from R-2's Type 3: Network LSA (R1+R2's network information) create its own Network LSA and send it to R-4.
R-4 now has the knowledge to add routes all of the way to R-1 into its routing table.
The same process would work in reverse from R-4 to R-1.
Type 4: Inter-Area Router LSA
ABRs create Type 4: Inter-Area LSAs and send them to other routers in an area to advertise the IP addresses of ASBRs that reside in a different area.
In the diagram below R1 will send a Type 1: Router LSA to R2 to share topology information about itself. The Type 4: Inter-Area Router LSA won't include information about ISP1 because it is outside the OSPFv3 process.
To advertise R1 (an ASBR) to R3, R2 (an ABR) will create and send a Type 4: Inter-Area Router LSA to R3.
Type 5: AS-External LSA
Type 5: AS-External LSAs advertise an external prefix that is redistributed into the OSPFv3 domain. It is common for an AS-External LSA to contain the default route of ::/0 pointing to the Internet.
The code in the routing table for AS-External LSAs is either O E1 or O E2
Note that each AS-External LSA can advertise only one prefix.
LSA Type 6: Group Membership
Type 6: Group Membership LSAs are for Multicast OSPF (MOSPF). They are rarely used and not supported by Cisco.