Which two link-state advertisement (LSA) types are allowed in a stub area? (Choose two.)
A.
LSA Type 1
B.
LSA Type 2
C.
LSA Type 4
D.
LSA Type 5
Explanation:
What are LSAs?The reachability information that is passed between the different routers in an OSPF domain are communicated via LSAs. There are several different types of LSA that communicate different pieces of information. In a normal area, all LSA types are allowed and communicated between the devices. A list of the different common LSAs is shown below:
LSA Type 1 Router Link Advertisements All OSPF devices send this LSA type, it contains the states of all of the interfaces that the device has in the OSPF domain. This LSA type is kept within a single area.
LSA Type 2 Network Link Advertisements Only Designated Routers (DR) send this type of LSA, it contains a list of devices connected to a particular network. This LSA type is kept within a single area.
Stubby Area Review
For those readers who have not read the previous OSPF area troubleshooting article, this section reviews the different types of OSPF stubby area and provides high level review of what they allow and deny into the specific area.Stubby A stubby area is an area that is not able to accept LSA type 5 which contains routes from outside the OSPF domain (Redistributed into OSPF), these are also referred to as external routes. Traffic that is destined for a location outside of the OSPF network is only able to exit the area via a default route (which is injected by the ABR).
Brief Explanation all LSA Types:
Type 1: router LSA — A router sends this to describe neighbors and its own interfaces.
Type 2: network LSA — For broadcast networks only; this LSA is flooded by the DR and lists OSPF-speaking routers on the network.
Type 3: network summary LSA — Sent by an ABR to advertise networks reachable through it. A stub area router will also use this for the default route.
Type 4: ASBR-summary LSA — Sent by ABR, but only internally. This describes to the others how to get to the ASBR itself, and uses only internal metrics.
Type 5: AS-external LSA — Used to describe external routes to internal areas. Can be used to advertise this is the way to the Internet (or some subset of).
Type 6: Group summary — Used in multicast (MOSPF). Ignore this.
Type 7: NSSA area import.
Type 8: External Attributes LSA – This is very rarely deployed and is used when BGP information is carried across OSPF AS.
Type 9, 10, 11 are Opaque LSAs — They are designated for future specifically for application specific purposes.