OSPF-7 Types of LSA

Because the OSPF protocol defines the types of routers, it is also necessary to define the types of various LSA advertisements.
For example: A DR Router must advertise multiple access links and all routers connected to the link, while other types of routers will not need to advertise this type of information.

Seven types of LSA for OSPF:
1. Router LSA (Router LSA)
Generated by all routers in the region, and can only be flooded within this region of the broadcast.

These most basic LSA Announcements list all of the routers ' links and interfaces, and indicate their status and the cost of outbound along each link direction.

2. NET LSA (network LSA)
Generated by a DR or BDR router in the region, including link information for the DR and BDR connected routers.

The network LSA is also flooding only within the region that generated the network LSA.

3. Network Rollup LSA (NET summary LSA)
Generated by the ABR, you can notify routers in the region to route information outside the region.

A default route that is outside a region but still inside an OSPF autonomous system can also be advertised through this LSA.

If an ABR router receives multiple network rollup LSA from the other ABR routers through the backbone area, the originating ABR router will select the least expensive LSA in these LSA advertisements and advertise the minimum cost of the LSA to the non-backbone area connected to it.

4. ASBR Rollup LSA (ASBR summary LSA)
is also generated by the ABR, but it is a host route that points to the ASBR router address.

5. Autonomous system external LSA (Autonomous System external LSA)
Generated by ASBR, which tells the path of the same autonomous region's router to the external autonomous region.

The external LSA of the autonomous system is the only LSA advertisement that is associated with a specific region and will be flooded throughout the autonomous system.

6, group member LSA (Group membership LSA) * Currently does not support multicast OSPF (MOSPF protocol)



7. NSSA external LSA (NSSA External LSA)
Generated by the ASBR, almost identical to the LSA 5 notification, but the NSSA external LSA advertises only flooding within the non-pure peripheral area of the originating NSSA external LSA notification.
In the Nssa area, when a router is ASBR, it has to generate LSA 5 messages, but the LSA 5 messages cannot be in the Nssa, and all ASBR generate LSA 7 messages to the routers in the region.


* With one exception, each ABR router advertises the default route with one type, the other. LSA types that allow flooding in each region

Zone Type 1&2 3&4 5 7
The backbone zone allows permission to allow not allowed
Non-backbone (non-distal) allow allow not allowed
The distal allow allow not allowed
Full distal allow not allowed disallow disallowed
NAAS allow allowed not allowed

* With one exception, each ABR router advertises the default route with one type, the other.

1 Peripheral areas: (Stub area)
The As external notification (LSA 5) is not allowed to flood within it. The ABR router at the peripheral boundary uses the Network Rollup LSA (LSA 3) to advertise the default route to this zone, and this default route is not advertised to the outside of the zone.
Router (Config-route) area 1 stub//zone 1 set as peripheral

2. Complete Peripheral Area: (totally stub)
Use the default route to reach the destination address outside of the OSPF autonomous system, and use the default route to reach all destination addresses outside the zone, and the ABR router in the complete peripheral area not only blocks LSA 5, it also blocks all summary lsa―― except the one that advertises the default route 3.
Router (Config-route) #area 1 stub no-summary//The area 1 is set to the full peripheral region, the Type 3 is replaced with the default route, No-summary is the role of the Type 3, 4 with the default route simplification

3 Non-pure peripheral area (Not-so-stubby-area)
Allowing external routes to be advertised inside the OSPF autonomous system while preserving the peripheral feature of the remainder of the autonomous system, ASBR advertises the external network to the LSA that originated type 7, and these Naas external LSA will flood the entire Naas area and be blocked on the ABR. The ABR converts type 7 to type 5 and advertises it to another region.

This article is from the "Sky" blog, please be sure to keep this source http://haikuotiankong.blog.51cto.com/633188/1695337

OSPF-7 Types of LSA