Exam SD-WAN-Engineer Topic 1 Question 10 Discussion

In a Data Center (DC) deployment, the ION device typically peers with a core router via Border Gateway Protocol (BGP) to exchange reachability information between the SD-WAN fabric and the legacy corporate network.2 When the ION is configured to learn only a default route ($0.0.0.0/0$) from the core, the entire SD- WAN fabric relies on this single BGP-learned route to reach internal resources not directly connected to the ION.
The primary risk in this design is network isolation caused by a BGP misconfiguration or a "soft failure" on the core router. If the BGP session stays "Up" but the core router stops advertising the default route due to a configuration error, the ION device will remove the route from its routing table. Without a valid path to the core, the branch sites connected to the DC ION will lose connectivity to all data center resources.
To mitigate this, the recommended best practice is to add a static default route with a higher Administrative Distance (AD) pointing to the core peer IPs.3 This acts as a "floating static route." Under normal operations, the BGP-learned default route (typically with an AD of 20 for eBGP) remains active in the routing table. If the BGP advertisement fails, the static route with the higher AD (e.g., 250) becomes active.
This ensures that the ION device maintains a persistent gateway toward the core infrastructure, preventing total fabric isolation and providing a fail-safe mechanism while the BGP peering issue is remediated. While BFD (Option A) helps with fast peer failure detection, it does not solve the issue of a missing prefix advertisement. Static route redundancy provides the necessary architectural "safety net" for the data center's reachability.