Associate Cloud Engineer Practice Questions

Answer: C

Why this is correct
The "Considerations for next hop instances" section gives an example with the same shape as this question (the page uses route-x, route-y, and route-z with 192.168.168.0/24 and 192.168.0.0/16). The next hop VMs of both routes to 10.8.8.0/24 (rt-1 and rt-2) are not running, so even though the next hop of rt-3 to the wider 10.8.0.0/16 is running, packets destined for addresses in 10.8.8.0/24 are dropped. The page explains the reason: in the Google Cloud routing order, the most specific destination step comes before the step that removes static and dynamic routes with unusable next hops.

Why the other options are wrong
"It is sent to the VM of rt-3, which has the lowest priority number" … In the routing order, the step that selects the most specific destination comes before the step that removes routes with unusable next hops. Once the /24 routes are selected, the /16 route of rt-3 is no longer a candidate.
"Priority selects rt-1, the others drop out, and the packet is dropped because its VM is stopped" … In another example on the page, when the next hop VM of the highest-priority route to the same destination is stopped, the packet is sent to the next-priority route whose VM is running. This is because the step removing routes with unusable next hops comes before the step removing lower-priority routes; the route is not fixed by priority before checking the VM state. The packet here is dropped because neither rt-1 nor rt-2 is usable.
"Because the next hop VMs are stopped, it is sent to the default internet gateway" … The page's example says that when the next hops of both /24 routes are not running, the packet is dropped. It is not rerouted by another path.

Key point
The routing order goes: select the most specific destination, remove static and dynamic routes with unusable next hops, then remove lower-priority routes. A route whose next hop VM is not running is removed as a route with an unusable next hop. Google Cloud does not stop you from stopping or deleting the next hop VM of a static route, so behavior depends on whether you keep another route with a running next hop for the same destination. Priority 0 is the highest and 65,535 the lowest.