If a host connected to switch Sw-AC3 sends an IP packet to destination 190.0.2.5 on a different subnet, what destination MAC address does the host use in the Ethernet frame?

Introduction / Context:
This question examines how a host encapsulates traffic when sending data to an IP address on a different subnet. It is a key concept in Cisco studies because it ties together IP routing, ARP, and the role of a default gateway in host communication beyond the local network.

Given Data / Assumptions:

• The host is connected to a switch (Sw-AC3) on some VLAN and has an IP configuration including subnet mask and default gateway.
• The destination IP address 190.0.2.5 is on a different IP subnet than the host.
• A router interface on the same VLAN acts as the default gateway for the host.

Concept / Approach:
When a host needs to send an IP packet to a destination outside its local subnet, it does not try to resolve the remote host's MAC address directly. Instead, it forwards the packet to its configured default gateway. ARP is used to resolve the MAC address of the default gateway interface on the local network. The Ethernet frame is then addressed to that MAC, while the inner IP packet retains the final destination IP of 190.0.2.5.

Step-by-Step Solution:
Step 1: The host compares its own IP address and subnet mask with the destination IP 190.0.2.5 and determines that the destination is on a different subnet.Step 2: Because the destination is remote, the host decides to send the packet to the default gateway router interface.Step 3: If the host does not already know the MAC address of the default gateway, it sends an ARP request asking "Who has the default gateway IP?"Step 4: The router interface responds with its MAC address. The host stores this mapping in its ARP cache.Step 5: The host builds an Ethernet frame with the destination MAC set to the router's interface MAC, source MAC set to its own interface MAC, and the payload containing an IP packet whose destination IP is still 190.0.2.5.

Verification / Alternative check:
Packet captures on the host LAN show that frames sent toward off-subnet destinations have the router's MAC as the destination. Only once the packet reaches the router does the router forward it toward the next hop, possibly rewriting the MAC header again on each routed hop.

Why Other Options Are Wrong:
Option A is incorrect because the host does not know the remote host's MAC address; ARP is limited to the local broadcast domain.Option C is wrong because switches forward frames based on MAC addresses but do not act as IP endpoints; hosts do not use the switch's MAC as a destination.Option D is incorrect because broadcast MAC is used only for discovery or special cases, not for regular unicast communication to remote networks.

Common Pitfalls:
Many beginners mistakenly think the host must somehow know the final recipient's MAC address. In routed networks, hosts only need to know the MAC of their default gateway for off-subnet destinations; routers handle the rest of the path hop by hop.

Final Answer:
The host uses The MAC address of the default gateway router interface connected to the host's VLAN as the destination MAC in the Ethernet frame.