VRRP Configuration on Pre-20.6 WAN Edge Router
An engineer must configure VRRP for redundancy on WAN Edge router 1 running an earlier version than 20.6, considering WAN Edge router2 is configured correctly. Which configuration meets the requirement?
Community Insight
The question tests VRRP placement in the service VPN plus interface state, and the trap is picking a snippet that parks VRRP under transport VPN 0 or leaves a subinterface administratively shut down.
This 300-415 question tests how VRRP must be placed on a Cisco Catalyst SD-WAN Edge running a release earlier than 20.6 while router 2 is already correct. The correct configuration puts VRRP inside the service-side VPN with all interfaces in no shutdown state, which corresponds to option A.
Options B and D were picked by some learners because they attempt to fix the 4-byte 802.1Q MTU overhead, but they fail the harder rule: VRRP is configured under the service-side VPN, and those snippets place interfaces in transport VPN 0.
Community Discussion (9 comments)
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Expert Analysis
Why the Answer Is Correct
VRRP in Cisco Catalyst SD-WAN is only supported on service-side interfaces, so the matching configuration must sit inside a service VPN (not VPN 0), which immediately narrows the choices to A and C. As Networkchamp87 quoted from Cisco's own VRRP documentation, "VRRP is only supported with service-side VPNs. If you are using subinterfaces, configure VRRP physical interfaces in VPN 0." Among the remaining two, option C leaves a subinterface (ge0/6.3) in shutdown state, which would break the redundant path, leaving option A as the only configuration that both scopes VRRP correctly and keeps the interfaces up for the earlier-than-20.6 router 1.Why the Other Options Are Wrong
Options B and D are wrong because they place the VRRP-relevant interface configuration under transport VPN 0, where VRRP is not supported, so any redundancy statement there is ineffective. Their focus on adjusting MTU to compensate for the dot1Q tag addresses a real 802.1Q overhead issue but does not satisfy the primary requirement of service-VPN placement. Option C is close and would be attractive if MTU handling were the deciding factor, but its subinterface is left in shutdown, so router 1 could never participate in the VRRP election. mikidvd51 rightly questioned whether shutdown versus no shutdown should be the discriminator, yet in an exam the administrative state is a legitimate correctness signal because a shut subinterface defeats the purpose of redundancy.Community Comment Notes
Outlaw_87 laid out the same elimination path, noting that "In Options B and D there are VPN 0, which is transport VPN" and that option C's ge0/6.3 is in shutdown, concluding with A, a chain Knowledge33 endorsed by writing "a is correct. Agree with Outlaw". Networkchamp87 backed this with the Cisco VRRP tracking documentation link, while D3n1s argued the opposite by prioritizing the MTU adjustment in D and ulkerra argued for C on MTU grounds, admitting "I couldn't find the answer in the given choices." LLMenterprise also rejected B, C, and D purely on the shutdown state of subinterface 6.2, showing the community broadly converged on service-VPN placement plus an up interface state.Official Reference
Exam Strategy
When a question references a software version cutoff such as earlier than 20.6, first re-apply the long-standing rules rather than version-specific behavior, since pre-20.6 releases require VRRP in the service-side VPN. Then eliminate any option whose interfaces are in shutdown or misassigned to VPN 0 before worrying about secondary details like MTU.
Frequently Asked Questions
Why is configuring VRRP under transport VPN 0 wrong here?
VRRP is only supported on service-side VPNs in Cisco SD-WAN, so any VRRP statement placed in VPN 0 takes effect on nothing and the routers never form a redundancy group.
Why does a shutdown subinterface eliminate option C?
A subinterface left in shutdown cannot send or receive VRRP hellos, so router 1 would never hold or back up the virtual gateway, defeating the redundancy the question requires.
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