Configuring OSPF Summary Routes to ASBR in SD-WAN
Short answer
D Enable RFC 1583 Compatible to ensure summary route costs are calculated according to the original OSPF standard.
Question
Key Takeaways
The core concept tested is the OSPF RFC compatibility setting for inter-area path cost calculation, with the common trap being confusion between RFC 1583 and non-RFC 1583 behaviors.
This question addresses configuring OSPF advanced parameters on Cisco Catalyst SD-WAN WAN Edge routers via vManager templates. It specifically focuses on the correct action to calculate summary route costs to an Autonomous System Boundary Router (ASBR).
Common mistake: Many users incorrectly select 'Disable RFC 1583 Compatible' or other options because they are unsure if the default behavior aligns with the requirement to use RFC 1583 standards.
Expert Analysis
Why the Answer Is Correct
To ensure that the branch WAN Edge router calculates summary route costs per the original OSPF standard defined in RFC 1583, you must enable the 'RFC 1583 Compatible' option. In Cisco IOS-XE (which underpins SD-WAN edge configurations), this is often achieved by ensuring the command compatible rfc1583 is active or not disabled. The default behavior in modern versions might be non-RFC 1583 (RFC 2328), so explicitly enabling compatibility ensures the correct cost calculation method for summary routes.
Why the Other Options Are Wrong
Options A and C ('Originate') relate to generating summary LSAs, which is a different function than calculating the cost of those summaries. Option B ('Disable RFC 1583 Compatible') would switch the router to use the newer RFC 2328 cost calculation, which contradicts the goal of using the RFC 1583 method.
Community Comment Notes
Community consensus strongly favors Option D. Users like Rosh8787 confirmed that restoring the RFC 1583 method requires the compatible setting, citing Cisco CLI documentation. While one user suggested disabling it, the majority and official logic support enabling compatibility to adhere to the older standard's cost metrics.
Official Reference
This link opens the official vendor documentation in a new tab.
Exam Strategy
When configuring OSPF on SD-WAN edges, always verify if the question specifies a particular RFC standard for cost calculation. If it mentions RFC 1583, look for settings that enforce compatibility with that version rather than the newer defaults.
Frequently Asked Questions
Why is Enable RFC 1583 Compatible required for ASBR summary routes?
What is the difference between Originate and RFC 1583 Compatible?
Community Votes
67% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 4 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 4
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Rosh8787 👍 1To restore the method used to calculate summary route costs per RFC 1583, use the compatible rfc1583 in router configuration mode. Hence Option D is correct https://www.cisco.com/c/en/us/td/docs/routers/sdwan/command/iosxe/qualified-cli-command-reference-guide/m-ospf-commands.html#GUID-C1C88B7E-F96C-4528-A72E-CBEACF1F6B20
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Knowledge33 👍 1 Answered Dhttps://www.cisco.com/c/en/us/td/docs/routers/sdwan/command/iosxe/qualified-cli-command-reference-guide/m-ospf-commands.html
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hamidreza0010 👍 1 Answered BB. Disable RFC 1583 Compatible.
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Gycu 👍 1 Answered DD is correct
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