An administrator configures a default gateway for the host. What is the purpose of a default gateway?

The destination IP address in a packet is never replaced by the default gateway address - the source host keeps the original destination IP intact and only changes the destination MAC address to that of the gateway when building the frame.

Only traffic destined for remote networks is sent to the default gateway; traffic bound for hosts on the same local subnet is sent directly via ARP resolution without involving the gateway.

When a host determines that a destination IP address is not on its local subnet (by comparing it against the subnet mask), it forwards the packet to the default gateway IP address for routing to remote networks. The default gateway acts as the exit point for all off-subnet traffic, allowing communication beyond the local broadcast domain.

The ARP table is populated as a side effect of ARP request/reply exchanges; the default gateway's role is routing decisions, not ARP table management.