OSPF Exam Questions With Correct
Answers
What type of routing protocol is OSPF? - answer✔✔OSPF is a link state routing protocol.
POP QUIZ: How frequently does OSPF send out routing updates? - answer✔✔OSPF sends out
routing updates every 30 minutes, and refreshes the LSDB for neighbor adjacencies.
POP QUIZ: How long does OSPF wait before considering a route previously learned, dead? -
answer✔✔The MaxAge timer is set to 60 minutes.
MaxAge is always 1 hour, and it has to be 1 hour on all platforms. The reason why is that
MaxAge is a special value that's used to flush a route out of the OSPF database.
For example if I have a connected link that's advertised into OSPF, and the link goes down, to
withdraw the link from other routers I re-flood it with MaxAge.
This is why the value has to be the same everywhere otherwise the routers couldn't properly
remove a route from the database.
What are the three main branches that can be broken down from link state routing protocol logic?
- answer✔✔You have
1. Neighbor discovery (neighbor table)
2. Topology database exchange (topology table)
3. Route computation (routing table)
What multicast address are OSPF hello packets sent to? - answer✔✔224.0.0.5
POP QUIZ: OSPF uses TCP/UDP for its transport protocol. T/F? - answer✔✔F.
It uses IP protocol 89.
EXAM STUDY MATERIALS July 26, 2024 9:30 AM
,What concept does OSPF use to segment LSDB flooding? - answer✔✔OSPF uses the concept of
"Area's" to segment LSDB flooding between peers.
How does OSPF decide upon its RID? - answer✔✔It's the exact same as EIGRP.
It checks to see if you:
1. Manually configured (first)
2. Highest IP address of an up/up Loopback interface
3. The highest IP address of any up/up non-loopback (physical) inteface
What do you have to do after changing the OSPF RID to take effect? - answer✔✔You need to
either run the `reload` or `clear ip ospf process` command.
It's an intrusive change, and will prompt you with a warning message before proceeding.
This is because it will tear down the OSPF neighbor relationship, and cause all links within that
area to recalculate their SPF tree.
How many OSPF neighbor states are there? - answer✔✔8
What are those 8 OSPF neighbor states? - answer✔✔Down
Attempt
Init
2-Way
Exstart
Exchange
Loading
Full
What is the purpose of each OSPF neighbor state? - answer✔✔Down:
This is the first OSPF neighbor state. It means that no information (hellos) has been received
from this neighbor, but hello packets can still be sent to the neighbor in this state.
EXAM STUDY MATERIALS July 26, 2024 9:30 AM
,During the fully adjacent neighbor state, if a router doesn't receive hello packet from a neighbor
within the RouterDeadInterval time (RouterDeadInterval = 4*HelloInterval by default) or if the
manually configured neighbor is being removed from the configuration, then the neighbor state
changes from Full to Down.
Attempt:
This state is only valid for manually configured neighbors in an NBMA environment. In Attempt
state, the router sends unicast hello packets every poll interval to the neighbor, from which hellos
have not been received within the dead interval.
Init:
This state specifies that the router has received a hello packet from its neighbor, but the receiving
router's ID was not included in the hello packet. When a router receives a hello packet from a
neighbor, it should list the sender's router ID in its hello packet as an acknowledgment that it
received a valid hello packet.
2-Way:
This state designates that bi-directional communication has been established between two
routers. Bi-directional means that each router has seen the other's hello packet. This state is
attained when the router receiving the hello packet sees its own Router ID within the received
hello packet's neighbor field. At this state, a router decides whether to become adjacent with this
neighbor. On broadcast media and non-broadcast multiaccess networks, a router becomes full
only with the designated router (DR) and the backup designated router (BDR); it stays in the 2-
way state with all other neighbors. On Point-to-point and Point-to-multipoint networks, a router
becomes full with all connected routers.
At the end of this stage, the DR and BDR
What does OSPF use to describe each neighbor state? - answer✔✔OSPF uses it's underlying
finite state machine (FSM) to represent its state changes.
What IP address does OSPF send multicast traffic to? - answer✔✔224.0.0.5
EXAM STUDY MATERIALS July 26, 2024 9:30 AM
, POP QUIZ: OSPF sends multicast traffic (hello packets) on a LAN when what two requirements
are met? - answer✔✔1. OSPF has been enabled on the interface, using either the `network`
statement in the OSPF instance, or you use the `ip ospf area` interface-level sub-command.
2. The interface has *not* been made passive using the `passive-interface` command from the
`router ospf <#> instance.
POP QUIZ: What type of OSPF enabled routers will stay in a 2-way state by default? -
answer✔✔DROTHERS
POP QUIZ: What routers will become fully adjacent (FULL state)? - answer✔✔Router's that are
part of a point-to-point link, or DR's and BDR's of their respective NBMA segment.
What DR and BDR multicast address are OSPF hello packets sent to? - answer✔✔224.0.0.6
What similar concept in relation to EIGRP does OSPF do with passive interfaces? - answer✔✔If
an interface is set to a passive state it won't send hello messages, but, it will still advertise that
subnet or prefix into OSPF.
What parameters must match in the hello packet to form an OSPF neighbor adjacency? -
answer✔✔1. Area
2. Hello and Dead Interval
3. Prefix/Subnet
4. Authentication
5. Stub Area Flag
What other additional parameters may be present in the OSPF hello packet? - answer✔✔1. RID
2. Reachable neighbors out that interface
3. Router priority
4. DR/BDR IP address
What is the purpose of hello packets? - answer✔✔Hello packets are used by EIGRP and OSPF
to create, and maintain neighbor adjacencies.
What is the hello and dead interval? - answer✔✔The OSPF "hello interval" is a periodic timer
that dictates how frequently hello packets need to be sent out a particular interface.
Conversely, if a hello is not received from a specific neighbor in a certain time frame, this is
known as the "dead interval."
EXAM STUDY MATERIALS July 26, 2024 9:30 AM
Answers
What type of routing protocol is OSPF? - answer✔✔OSPF is a link state routing protocol.
POP QUIZ: How frequently does OSPF send out routing updates? - answer✔✔OSPF sends out
routing updates every 30 minutes, and refreshes the LSDB for neighbor adjacencies.
POP QUIZ: How long does OSPF wait before considering a route previously learned, dead? -
answer✔✔The MaxAge timer is set to 60 minutes.
MaxAge is always 1 hour, and it has to be 1 hour on all platforms. The reason why is that
MaxAge is a special value that's used to flush a route out of the OSPF database.
For example if I have a connected link that's advertised into OSPF, and the link goes down, to
withdraw the link from other routers I re-flood it with MaxAge.
This is why the value has to be the same everywhere otherwise the routers couldn't properly
remove a route from the database.
What are the three main branches that can be broken down from link state routing protocol logic?
- answer✔✔You have
1. Neighbor discovery (neighbor table)
2. Topology database exchange (topology table)
3. Route computation (routing table)
What multicast address are OSPF hello packets sent to? - answer✔✔224.0.0.5
POP QUIZ: OSPF uses TCP/UDP for its transport protocol. T/F? - answer✔✔F.
It uses IP protocol 89.
EXAM STUDY MATERIALS July 26, 2024 9:30 AM
,What concept does OSPF use to segment LSDB flooding? - answer✔✔OSPF uses the concept of
"Area's" to segment LSDB flooding between peers.
How does OSPF decide upon its RID? - answer✔✔It's the exact same as EIGRP.
It checks to see if you:
1. Manually configured (first)
2. Highest IP address of an up/up Loopback interface
3. The highest IP address of any up/up non-loopback (physical) inteface
What do you have to do after changing the OSPF RID to take effect? - answer✔✔You need to
either run the `reload` or `clear ip ospf process` command.
It's an intrusive change, and will prompt you with a warning message before proceeding.
This is because it will tear down the OSPF neighbor relationship, and cause all links within that
area to recalculate their SPF tree.
How many OSPF neighbor states are there? - answer✔✔8
What are those 8 OSPF neighbor states? - answer✔✔Down
Attempt
Init
2-Way
Exstart
Exchange
Loading
Full
What is the purpose of each OSPF neighbor state? - answer✔✔Down:
This is the first OSPF neighbor state. It means that no information (hellos) has been received
from this neighbor, but hello packets can still be sent to the neighbor in this state.
EXAM STUDY MATERIALS July 26, 2024 9:30 AM
,During the fully adjacent neighbor state, if a router doesn't receive hello packet from a neighbor
within the RouterDeadInterval time (RouterDeadInterval = 4*HelloInterval by default) or if the
manually configured neighbor is being removed from the configuration, then the neighbor state
changes from Full to Down.
Attempt:
This state is only valid for manually configured neighbors in an NBMA environment. In Attempt
state, the router sends unicast hello packets every poll interval to the neighbor, from which hellos
have not been received within the dead interval.
Init:
This state specifies that the router has received a hello packet from its neighbor, but the receiving
router's ID was not included in the hello packet. When a router receives a hello packet from a
neighbor, it should list the sender's router ID in its hello packet as an acknowledgment that it
received a valid hello packet.
2-Way:
This state designates that bi-directional communication has been established between two
routers. Bi-directional means that each router has seen the other's hello packet. This state is
attained when the router receiving the hello packet sees its own Router ID within the received
hello packet's neighbor field. At this state, a router decides whether to become adjacent with this
neighbor. On broadcast media and non-broadcast multiaccess networks, a router becomes full
only with the designated router (DR) and the backup designated router (BDR); it stays in the 2-
way state with all other neighbors. On Point-to-point and Point-to-multipoint networks, a router
becomes full with all connected routers.
At the end of this stage, the DR and BDR
What does OSPF use to describe each neighbor state? - answer✔✔OSPF uses it's underlying
finite state machine (FSM) to represent its state changes.
What IP address does OSPF send multicast traffic to? - answer✔✔224.0.0.5
EXAM STUDY MATERIALS July 26, 2024 9:30 AM
, POP QUIZ: OSPF sends multicast traffic (hello packets) on a LAN when what two requirements
are met? - answer✔✔1. OSPF has been enabled on the interface, using either the `network`
statement in the OSPF instance, or you use the `ip ospf area` interface-level sub-command.
2. The interface has *not* been made passive using the `passive-interface` command from the
`router ospf <#> instance.
POP QUIZ: What type of OSPF enabled routers will stay in a 2-way state by default? -
answer✔✔DROTHERS
POP QUIZ: What routers will become fully adjacent (FULL state)? - answer✔✔Router's that are
part of a point-to-point link, or DR's and BDR's of their respective NBMA segment.
What DR and BDR multicast address are OSPF hello packets sent to? - answer✔✔224.0.0.6
What similar concept in relation to EIGRP does OSPF do with passive interfaces? - answer✔✔If
an interface is set to a passive state it won't send hello messages, but, it will still advertise that
subnet or prefix into OSPF.
What parameters must match in the hello packet to form an OSPF neighbor adjacency? -
answer✔✔1. Area
2. Hello and Dead Interval
3. Prefix/Subnet
4. Authentication
5. Stub Area Flag
What other additional parameters may be present in the OSPF hello packet? - answer✔✔1. RID
2. Reachable neighbors out that interface
3. Router priority
4. DR/BDR IP address
What is the purpose of hello packets? - answer✔✔Hello packets are used by EIGRP and OSPF
to create, and maintain neighbor adjacencies.
What is the hello and dead interval? - answer✔✔The OSPF "hello interval" is a periodic timer
that dictates how frequently hello packets need to be sent out a particular interface.
Conversely, if a hello is not received from a specific neighbor in a certain time frame, this is
known as the "dead interval."
EXAM STUDY MATERIALS July 26, 2024 9:30 AM
