Section 1.3 - OSPF Area and LSA Types

Question 1

What are the characteristics of a regular area?

Answer 1

• accepts link updates, route summaries, and external routes

Question 2

What are the characteristics of a backbone area (transit area)?

Answer 2

• all other areas connect here
• denoted as Area 0
• includes all properties of a standard OSPF area

Question 3

What are the characteristics of a stub area?

Answer 3

• does not accept info about routes that are external to the AS (e.g. non-OSPF sources)
• to route traffic outside of the AS, they use a default route
• cannot contain ASBRs, except that ABRs may also be ASBRs

Question 4

What are the characteristics of a totally stubby area?

Answer 4

• does not accept external AS routes or summary routes from other areas that are internal to the AS
• to send a packet to a network external to the area, it uses a default route
• cannot contain ASBRs, except that ABRs may also be ASBRs

Question 5

What are the characteristics of a not-so-stubby (NSSA) area?

Answer 5

• special type 7 LSA
• similar to stubby, but allows ASBRs

Question 6

What are the characteristics of a totally not-so-stubby (totally NSSA) area?

Answer 6

• does not accept external AS routes or summary routes from other areas that are internal to the AS
• contains routing info and external (LSA 7) routing info
• Cisco proprietary

Question 7

What is OSPF LSA Type 1 (Router) for?

Answer 7

• describe the state of the router links to the area and are flooded just in that area

Question 8

What is OSPF LSA Type 2 (Network) for?

Answer 8

• DRs generate network link advertisements for multiaccess networks
• describe the set of routers that are attached to a particular multiaccess network
• flooded in the area that contains the network

Question 9

What is OSPF LSA Type 3 (Summary) for?

Answer 9

• ABR summary
• based on info it received from other areas (LSA 1/2)
• the link entries are not flooded into totally stubby areas or NSSAs

Question 10

What is OSPF LSA Type 4 (Summary ASBR) for?

Answer 10

• ASBR summary
• ABRs generate summary advertisements that describe routes to ASBRs
• flooded throughout the backbone area to other ABRs
• not flooded in totally stubby and NSSA areas

Question 11

What is OSPF LSA Type 5 (Autonomous System External) for?

Answer 11

• ASBRs generate AS external link advertisements
• describes routes to destinations that are external to the AS
• flooded everywhere except for stub areas, totally stub areas, NSSAs, and totally NSSAs

Question 12

What is OSPF LSA Type 7 (NSSA) for?

Answer 12

• used in NSSAs for external routes

Question 13

What is the difference between an LSA 3 and an LSA 4?

A) LSA 3 is a summary for internal networks, and LSA 4 carries external networks
B) LSA 3 carries external networks, and LSA 4 is a summary
C) LSA 3 is a summary for ASBRs, and LSA 4 is a summary for networks
D) LSA 3 is a summary for networks, and LSA 4 is a summary for ASBRs
E) LSA 3 is used only for IPv4, and LSA 4 can be used for IPv4 and IPv6

Answer 13

D