Refer to the exhibit. An engineer must verify the operational status of ISP 1 by testing the IP reachability of the ISP1 DNS server every 10 seconds. If the DNS server is not reachable from the CPE th

`ip route 0.0.0.0 0.0.0.0 198.51.100.1` is a default route. While it would send traffic for the DNS server out Gi0/0 if no more specific route exists, a specific host route (choice C) is more appropriate for ensuring the IP SLA probe consistently uses the intended ISP path, especially in scenarios with multiple default routes or dynamic routing.

`ip route 0.0.0.0 255.255.255.255 198.51.100.1` is syntactically incorrect for a standard default route; a default route typically uses a `0.0.0.0 0.0.0.0` network/mask.

This command defines a specific static route for the ISP1 DNS server (198.51.100.252) via the ISP1 gateway (198.51.100.1). This host route ensures that any traffic destined for the DNS server, including the IP SLA probe, will explicitly use the ISP1 path, fulfilling the requirement to test reachability through the Gi0/0 interface's next hop.

`ip sla 1` initiates the configuration for an IP Service Level Agreement operation, which is used to monitor network performance and reachability. Within this mode, specific parameters like the `icmp-echo` type, the target IP (198.51.100.252), source interface (Gi0/0), and frequency (every 10 seconds) would be defined to perform the required reachability test.

This choice is identical to D. The question asks for two distinct configuration sets, and while `ip sla 1` is correct, choice C provides the essential routing configuration to direct the SLA probe correctly.