352-001 · Question #547
Which OSPF design consideration, with regards to simplicity and address preservation, must be considered when connecting two Layer 3 switches directly using 10 GBASE-T cabling and formatting an OSPF n
The correct answer is E. The OSPF network type must be set to point-to-point. When two Layer 3 switches are connected directly via a point-to-point link, setting the OSPF network type to point-to-point eliminates unnecessary DR/BDR election and allows /31 subnets to conserve IP addresses.
Question
Which OSPF design consideration, with regards to simplicity and address preservation, must be considered when connecting two Layer 3 switches directly using 10 GBASE-T cabling and formatting an OSPF neighbor adjacency?
Options
- AMesh groups must be included in the design
- BThe OSPF Hello and Dead timers must be tuned to detect failures as quickly as possible
- CThe OSPF network type must be set to point-to-multipoint
- DAn OSPF neighbor adjacency formed over loopback interfaces must be placed in Area 0
- EThe OSPF network type must be set to point-to-point
How the community answered
(27 responses)- A4% (1)
- B4% (1)
- C7% (2)
- E85% (23)
Why each option
When two Layer 3 switches are connected directly via a point-to-point link, setting the OSPF network type to point-to-point eliminates unnecessary DR/BDR election and allows /31 subnets to conserve IP addresses.
Mesh groups are an OSPF feature for NBMA networks used to control flooding and are not applicable to a direct two-switch physical connection.
Tuning Hello and Dead timers addresses failure detection speed, not the simplicity or address-conservation concerns stated in the question.
Point-to-multipoint network type is designed for hub-and-spoke topologies where one interface reaches multiple remote peers, not for a direct physical link between two switches.
Placing loopback-based adjacencies in Area 0 is a backbone adjacency design pattern unrelated to the design considerations for a direct 10GBASE-T physical link.
Ethernet interfaces default to the OSPF broadcast network type, which triggers a DR/BDR election even on a two-device segment where it provides no benefit, adding unnecessary complexity. Setting the OSPF network type to point-to-point removes the DR/BDR requirement and supports /31 prefix addressing per RFC 3021, satisfying both the simplicity and address preservation design goals simultaneously.
Concept tested: OSPF point-to-point network type on direct Layer 3 links
Source: https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13683-20.html
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