ACSP OSPF Routing Configuration 4 — Questions and Answers
Question 1: An Aruba switch is configured with OSPF authentication on an interface using 'ip ospf authentication message-digest'. What must match between neighbors for the adjacency to form?
- The MD5 key-id and key string must match on both sides (Correct answer)
- Only the key string must match; key-id is locally significant
- Authentication type must match, but keys are exchanged automatically
- MD5 authentication only requires matching area IDs
Correct answer: The MD5 key-id and key string must match on both sides
For MD5 OSPF authentication, both the key-id and the key string must match on neighboring routers; a mismatch in either will prevent adjacency formation.
Question 2: What is the effect of configuring 'ip ospf priority 0' on an Aruba switch interface participating in a broadcast segment?
- The interface becomes ineligible for DR/BDR election (Correct answer)
- The interface becomes the DR
- The interface sends hellos but abstains from LSA flooding
- The interface's OSPF cost is set to 0
Correct answer: The interface becomes ineligible for DR/BDR election
Setting OSPF priority to 0 makes the router ineligible to be elected as DR or BDR on that segment, useful for leaf switches that should never be DRs.
Question 3: In an Aruba OSPF deployment, which condition causes an OSPF router to transition from EXSTART to EXCHANGE state?
- Successful election of master/slave and agreement on initial sequence number (Correct answer)
- Receipt of the first DBD packet from the neighbor
- Completion of LSR/LSU/LSAck exchange
- The dead interval expiring without a hello
Correct answer: Successful election of master/slave and agreement on initial sequence number
The EXSTART-to-EXCHANGE transition occurs after master/slave negotiation completes and both routers agree on the initial DBD sequence number.
Question 4: An Aruba switch is an ABR between Area 0 and Area 1. Area 1 is configured as a totally stubby area. What routes does the ABR advertise into Area 1?
- Only a default route (Type 3 LSA) (Correct answer)
- All inter-area and external routes plus a default route
- Only intra-area Type 1 and Type 2 LSAs
- Only Type 5 external LSAs
Correct answer: Only a default route (Type 3 LSA)
In a totally stubby area, the ABR blocks all Type 3, 4, and 5 LSAs and injects only a single default route as a Type 3 LSA, minimizing the LSDB.
Question 5: When configuring OSPF virtual links on an Aruba switch, what is the transit area used for?
- To logically connect a disconnected area to Area 0 by traversing another area (Correct answer)
- To provide redundancy between two Area 0 segments
- To carry Type 5 LSAs between stub areas
- To replace physical links between ABRs
Correct answer: To logically connect a disconnected area to Area 0 by traversing another area
A virtual link extends the backbone (Area 0) through a transit area to connect a non-backbone area that lacks a physical connection to Area 0.
Question 6: Which Aruba AOS-CX command displays the OSPF neighbor state and the dead timer countdown for all OSPF neighbors?
- show ip ospf neighbor (Correct answer)
- show ip ospf database
- show ip ospf interface
- show ip route ospf
Correct answer: show ip ospf neighbor
The 'show ip ospf neighbor' command lists all OSPF neighbors with their state, dead time, interface, and router-id.
Question 7: On an Aruba switch, the OSPF SPF algorithm is triggered after a topology change. What is the purpose of SPF throttling?
- To delay successive SPF calculations and prevent CPU overload during instability (Correct answer)
- To reduce the LSA flooding scope during reconvergence
- To prioritize intra-area routes during SPF recalculation
- To limit the number of OSPF neighbors that can trigger SPF
Correct answer: To delay successive SPF calculations and prevent CPU overload during instability
SPF throttling introduces configurable delays between SPF runs so that rapid topology changes don't cause continuous CPU-intensive SPF recalculations.
ACSP OSPF Routing Configuration 4
An Aruba switch is configured with OSPF authentication on an interface using 'ip ospf authentication message-digest'.
What must match between neighbors for the adjacency to form?