Comprehensive and Detailed Explanation:

A default route is used when no specific route matches a destination IP.

The correct syntax for a default static route is:

ip route-static 0.0.0.0 0.0.0.0

✅ Correct Option:

A. [Huawei] ip route-static 0.0.0.0 0.0.0.0 192.168.1.1

This correctly sets 192.168.1.1 as the next-hop for all unknown destinations.

❌ Incorrect Options:

B. 0.0.0.0 0.0.0.0 0.0.0.0 → Invalid because 0.0.0.0 cannot be a next-hop.

C. 0.0.0.0 255.255.255.255 192.168.1.1 → Invalid because the mask must be 0.0.0.0 for a default route.

D. [Huawei-Serial0] ip route-static 0.0.0.0 0.0.0.0 0.0.0.0 → Invalid interface syntax.

✅ Reference: HCIA-Datacom Routing Guide – Default Route Configuration