ICND1 OSPF Configuration 2 — Questions and Answers
Question 1: Which OSPF network type is assigned by default on a Cisco Ethernet interface?
- Point-to-point
- Non-broadcast
- Broadcast (Correct answer)
- Point-to-multipoint
Correct answer: Broadcast
Ethernet interfaces default to the OSPF broadcast network type, which elects a DR and BDR.
Question 2: What is the OSPF router ID selection order when no explicit router-id is configured?
- Lowest IP on any interface, then highest loopback
- Highest loopback IP, then highest active interface IP (Correct answer)
- Lowest loopback IP, then lowest active interface IP
- Randomly assigned by the OSPF process
Correct answer: Highest loopback IP, then highest active interface IP
OSPF prefers the highest loopback IP as the router ID; if none exists, it uses the highest active physical interface IP.
Question 3: Which command changes the OSPF hello interval on an interface to 5 seconds?
- router ospf hello-interval 5
- ip ospf hello-interval 5 (Correct answer)
- ospf timers hello 5
- ip ospf timers hello 5
Correct answer: ip ospf hello-interval 5
The interface-level command 'ip ospf hello-interval 5' sets the OSPF hello interval to 5 seconds.
Question 4: What happens when OSPF hello and dead timers are mismatched between two routers?
- Routers form adjacency but exchange routes slowly
- Routers form adjacency and negotiate a common timer
- Routers cannot form an adjacency (Correct answer)
- Routers use the lower timer value automatically
Correct answer: Routers cannot form an adjacency
OSPF requires matching hello and dead timers on both sides; a mismatch prevents adjacency formation.
Question 5: Which OSPF packet type is used to acknowledge receipt of LSAs?
- Hello
- Database Description (DBD)
- Link-State Acknowledgment (LSAck) (Correct answer)
- Link-State Request (LSR)
Correct answer: Link-State Acknowledgment (LSAck)
LSAck packets provide reliable delivery acknowledgment for LSUs containing LSAs.
Question 6: In OSPF, what is the function of the Database Description (DBD) packet?
- Requests specific LSAs from a neighbor
- Summarizes the contents of the LSDB during adjacency formation (Correct answer)
- Acknowledges received LSAs
- Floods LSAs throughout the OSPF area
Correct answer: Summarizes the contents of the LSDB during adjacency formation
DBD packets summarize the router's LSDB entries so neighbors can compare and identify missing LSAs.
Question 7: Which OSPF state comes immediately after the Two-Way state during adjacency formation on a broadcast network?
- Full
- Loading
- ExStart (Correct answer)
- Exchange
Correct answer: ExStart
After Two-Way, routers enter ExStart to negotiate the master/slave relationship before exchanging DBD packets.
ICND1 OSPF Configuration 2
Which OSPF network type is assigned by default on a Cisco Ethernet interface?