Lecture OSPF Flashcards
(33 cards)
What is OSPF?
OSPF (Open Shortest Path First) is a link-state routing protocol that uses the concept of areas and relies on bandwidth and delay to calculate the best path.
What are the different types of OSPF?
Single-area OSPF (uses area 0) and Multi-area OSPF.
What information does OSPF advertise?
Link-state information.
What tables does OSPF use and what are they built from?
Hello packets => Adjacency table
Database => Topology table
SPF => Routing table
What is a limitation of RIP that OSPF addresses?
RIP uses hop count as a metric, while OSPF uses bandwidth and delay.
Describe the Adjacency Database (Neighbor Table).
Lists all neighboring routers with bidirectional communication.
Unique for each router.
Viewed with show ip ospf neighbor.
Describe the Topology Table (Link-state Database).
Lists information about all routers in the network.
Represents the network topology.
Identical LSDB within an area.
Viewed with show ip ospf database.
Describe the Routing Table (Forwarding Database).
Lists routes generated by the SPF algorithm.
Unique for each router.
Contains information on how and where to send packets.
Viewed with show ip route ospf or show ip route.
What are the 5 OSPF packet types (LSAs)?
Hello
Database Description (DBD)
Link-State Request (LSR)
Link-State Update (LSU)
Link-State Acknowledgment (LSAck)
What is the purpose of Hello packets?
Discover neighbors and establish adjacencies.
What is the purpose of DBD packets?
Check for database synchronization between routers.
What is the purpose of LSR packets?
Request specific link-state records
What is the purpose of LSU packets?
Send specifically requested link-state records.
What is the purpose of LSAck packets?
Acknowledge other packet types.
List some LSA types.
Router LSAs (Type 1)
Network LSAs (Type 2)
Summary LSAs (Type 3 or 4)
Autonomous System External LSAs (Type 5)
List and describe OSPF router states.
- Down State: No Hello packets received.
-Init State: Router sends Hello packets, receives Hello packets with the sending router’s Router ID. - Two-Way State: Bidirectional communication, DR/BDR election on multiaccess links.
- ExStart State: Routers decide who initiates DBD exchange and initial DBD sequence number.
- Exchange State: Routers exchange DBD packets, may proceed to Loading or Full state.
- Loading State: LSRs and LSUs are used to get missing information, SPF algorithm is run.
- Full State: Link-state database is synchronized.
What happens in the Two-Way State?
Communication becomes bidirectional, and DR/BDR election occurs on multiaccess links.
What is DR and BDR?
DR (Designated Router) and BDR (Backup Designated Router) are elected on multiaccess networks to reduce the number of adjacencies.
How is OSPF cost calculated?
Cost = reference bandwidth / interface bandwidth (Cost = 100,000,000 bps / interface bandwidth in bps)
What are the types of IDs used in OSPF?
Process ID, Area ID, Router ID.
What are some OSPF verification commands and what do they show?
show ip ospf neighbors: Verifies adjacency, shows neighbor’s IP, states, priority, and Router ID.
show ip protocols: Shows OSPFv2 process ID, Router ID, interface OSPF configuration, distance value.
show ip ospf: Shows OSPFv2 process ID and Router ID, area info, last SPF execution.
show ip ospf interface: Shows process ID, local Router ID, network type, OSPF cost, DR/BDR info, neighbors.
show ip route: Shows routing table, AD, metric (cost).
How do you configure the OSPF reference bandwidth?
R1(config)# router ospf 10
R1(config-router)#auto-cost reference-bandwidth Mbps
(Adjust Mbps to the desired value)
How do you manually set the OSPF cost on an interface?
R1(config)# interface g0/0
R1(config-if)#ip ospf cost value
(Replace g0/0 with the interface and value with the cost)
How do you configure the OSPF Hello interval on an interface?
R1(config-if)#ip ospf hello-interval seconds
(Replace seconds with the desired interval)
