With which OSPF network type will routers form full adjacencies but not perform a DR and BDR election process?

Introduction / Context:
OSPF behaves differently on various network types. On broadcast and non-broadcast multi-access segments, OSPF elects a designated router and a backup designated router to reduce the number of adjacencies and the amount of flooding. On other network types such as point-to-point links, DR and BDR elections are not needed. Understanding which types use DR or BDR is key to designing and troubleshooting OSPF networks.

Given Data / Assumptions:

• OSPF runs on links of different network types, including point-to-point and multi-access networks.
• Routers always need to form adjacencies to exchange link state information.
• The question is about the network type where no DR or BDR is elected.
• DR or BDR elections are associated with segments that support multiple OSPF routers on a common medium.

Concept / Approach:
On broadcast multi-access networks, such as Ethernet segments with multiple OSPF routers, OSPF elects a DR and a BDR to act as central points for LSDB synchronization and LSA flooding. On non-broadcast multi-access networks like certain Frame Relay topologies, OSPF can also elect a DR and BDR if configured accordingly. However, on point-to-point links that connect exactly two OSPF routers, there is no need for DR or BDR because each router already has a direct relationship with the other. Therefore, OSPF does not perform a DR or BDR election on point-to-point network types.

Step-by-Step Solution:
Step 1: Recall that DR and BDR elections occur on OSPF network types where more than two routers can share a common multi-access segment.Step 2: Recognize that broadcast multi-access and non-broadcast multi-access networks fall into this category.Step 3: Understand that a point-to-point link connects only two routers, so every LSA can be directly exchanged without the need for a designated router.Step 4: From this, conclude that OSPF does not perform DR or BDR elections on point-to-point network types, even though full adjacencies still form.Step 5: Note that area 0 is a logical backbone designation, not a physical network type, and is not directly related to DR or BDR elections.

Verification / Alternative check:
On Cisco routers, you can use show ip ospf interface to see the network type and whether a DR or BDR has been elected. On point-to-point interfaces such as serial links configured for point-to-point OSPF, the output shows that no DR or BDR is present, confirming the behaviour described above.

Why Other Options Are Wrong:
Option B refers to backbone area 0, which is an OSPF area designation, not a specific network type. DR and BDR elections can still occur within area 0 on multi-access networks.Option C, broadcast multi-access, is exactly the network type where DR and BDR elections are required and most commonly seen.Option D, non-broadcast multi-access, also supports DR and BDR elections, though configuration details can vary.Option E, virtual link, is a special OSPF mechanism for connecting areas to the backbone and does not itself describe a standard network type for adjacency and DR election.

Common Pitfalls:
Students sometimes confuse logical OSPF areas with physical network types or assume that DR and BDR elections always occur. Remember that point-to-point links have only two routers, so DR or BDR roles would add unnecessary complexity without any benefit. Focusing on whether the medium is multi-access or point-to-point helps clarify when elections occur.

Final Answer:
OSPF forms adjacencies without DR or BDR elections on the Point-to-point network type.