352-001 · Question #399
You are redesigning an OSPF v2 network and must migrate some links. You are concerned that there are different subnet masks. Which link type will still form an OSPF adjacency even if there are subnet
The correct answer is D. point-to-point. OSPF point-to-point links skip subnet mask verification during neighbor adjacency formation, making them the only link type that tolerates mismatched masks.
Question
You are redesigning an OSPF v2 network and must migrate some links. You are concerned that there are different subnet masks. Which link type will still form an OSPF adjacency even if there are subnet mask mismatches?
Options
- Abroadcast
- Bpoint-to-multipoint
- Cnon-broadcast
- Dpoint-to-point
How the community answered
(35 responses)- A3% (1)
- B6% (2)
- D91% (32)
Why each option
OSPF point-to-point links skip subnet mask verification during neighbor adjacency formation, making them the only link type that tolerates mismatched masks.
Broadcast network types require matching subnet masks in OSPF hello packets, and a mismatch will prevent adjacency formation.
Point-to-multipoint networks also validate subnet masks during the neighbor discovery process, so a mismatch will block adjacency.
Non-broadcast (NBMA) networks require matching subnet masks just like broadcast types, and mismatches will cause neighbor formation to fail.
On point-to-point OSPF links, the subnet mask is not checked as part of the hello packet validation process, so neighbors will still form an adjacency even with mismatched masks. All other OSPF network types (broadcast, non-broadcast, point-to-multipoint) require matching subnet masks because they use the mask to verify that neighbors belong to the same network segment. This behavior makes point-to-point the correct choice when migrating links with inconsistent subnet configurations.
Concept tested: OSPF network types and subnet mask adjacency rules
Source: https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-1.html
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