OSPF Cheat Sheet

Question 1

Internal Router

Answer 1

All interfaces reside within the same area

Question 2

Backbone Router

Answer 2

A router with an interface in area 0 ( the backbone)

Question 3

ABR(Area Border Router)

Answer 3

Connects two or more areas

Question 4

ASBR(AS Boundary Router)

Answer 4

Router that is connected to other OSPF areas as well as other routing protocols

Question 5

LSA: Router Link (Type 1)

Answer 5

Lists directly connected links of router and the cost to each; flooded within an area

Question 6

LSA: Network Link (Type 2)

Answer 6

Generated by DR; sends out info about the state of other routers that are part of the same network

Question 7

LSA: Network Summary (Type 3)

Answer 7

Generated by an ABR and advertises networks/inter- area routes to the backbone area (area 0)

Question 8

LSA: ASBR Summary (Type 4)

Answer 8

Generated by ABR, used to inform the rest of the OSPF areas how to get to the autonomous system boundary router (ASBR)

Question 9

7 stages to become neighbor in OSPF. Explain them.

Answer 9

1. Down: no OSPF neighbor detected
2. Init: Hello packet received
3. Two-Way:own router ID found in received hello packet
4. Exstart: master and slave roles determined
5. Exchange: database description packets (DBD) are sent
6. Loading: exchange of LSRs(Link state request) and LSUs (Link state update) packets
7. Full: OSPF routers now have an adjacency

Question 10

Point-to-Point Network Type

DR/BDR Elected:
Neighbor Discovery:
Hello/Dead Timers:
Supported Topology:

Answer 10

DR/BDR Elected: No
Neighbor Discovery: Yes
Hello/Dead Timers: 10/40
Supported Topology: Point-to-Point

Question 11

Broadcast Network Type

DR/BDR Elected:
Neighbor Discovery:
Hello/Dead Timers:
Supported Topology:

Answer 11

DR/BDR Elected: Yes
Neighbor Discovery: Yes
Hello/Dead Timers: 10/40
Supported Topology: Full Mesh