300-730 · Question #130
Which feature allows a DMVPN Phase 3 spoke to switch to an alternate hub when the primary hub is unreachable?
The correct answer is B. backup NHS. DMVPN spoke redundancy relies on the backup NHS feature, which designates an alternate hub router that spokes can register with if the primary hub becomes unreachable.
Question
Options
- Amulticast PIM
- Bbackup NHS
- Cper-tunnel jitter probes
- DNHRP shortcut
How the community answered
(43 responses)- A2% (1)
- B88% (38)
- C2% (1)
- D7% (3)
Why each option
DMVPN spoke redundancy relies on the backup NHS feature, which designates an alternate hub router that spokes can register with if the primary hub becomes unreachable.
Multicast PIM handles multicast traffic distribution and routing group memberships, and has no role in hub failover or NHS redundancy.
NHRP allows spokes to be configured with both a primary and backup Next Hop Server using 'ip nhrp nhs' statements with priority values. When the primary hub fails NHRP reachability checks, the spoke automatically registers with the backup NHS and uses it to resolve tunnel endpoints. This provides seamless hub redundancy without manual intervention.
Per-tunnel jitter probes are an IP SLA mechanism for measuring delay variation on tunnels, not a failover mechanism for switching to an alternate hub.
NHRP shortcuts in Phase 3 enable spoke-to-spoke direct tunnel creation bypassing the hub for data traffic, but do not provide hub redundancy or failover capability.
Concept tested: DMVPN hub redundancy via backup NHS
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_nhrp/configuration/xe-16/irn-xe-16-book/irn-dmvpn.html
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