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In an ARP reply, the dst-mac refers specifically to the MAC address of the device that originally sent the ARP request. When a device wants to know the MAC address corresponding to a specific IP address, it sends an ARP request that includes its own MAC address as the source and the target IP address for which it wants the MAC address.

In the ARP reply, the device that owns the requested IP address sends back its MAC address. The dst-mac in this context is the target address for the response, indicating that the MAC address being provided is intended for the original requester. This is essential for the ARP protocol's operation, as it ensures that network devices can communicate using the correct MAC addresses.

As a result, in the ARP reply, the header destination, which is reflected in dst-mac, aligns with the MAC address of the device that initiated the ARP request, thus confirming the correspondence between the IP address and the MAC address provided in the response. The destination MAC address must match the initial sender of the ARP request for effective communication to occur.