When transmitting to a remote destination, what two things will occur after a host has determined the IP address of the destination to which it is transmitting? (Choose two.)
A. The sending host will perform an ARP broadcast in its local subnet using the IP address of the destination host.
B. The sending host will perform an ARP broadcast in its local subnet using the IP address of the local router interface.
C. The local router interface will respond with the MAC address of the destination host.
D. The local router interface will respond with its own MAC address.
E. The destination host will respond with its own MAC address.
Correct Answer: B, D
Explanation:
When a transmission is made to a remote location, the sending host will perform an Address Resolution Protocol (ARP) broadcast in its local subnet using the IP address of the local router interface, and the local router interface will respond with its own MAC address. A remote address is defined as an address in a different subnet.
When a host determines (through a process called ANDing) that a destination address is remote, it will send the packet to the local router interface, which is known as the default gateway on the host. But when it performs ANDing on the IP address of the local router interface, it will discover that the interface is local. When
transmitting to a local IP address, a conversion to a MAC address must occur. Therefore, it will perform a local ARP broadcast, and the local router interface will respond with its MAC address.
Regardless of whether the host is broadcasting for the MAC address of the destination locally on the same LAN, or if it is broadcasting for the MAC address of the router interface (remotely), the broadcast will be a Layer 2 broadcast using the MAC address ff-ff-ff-ff-ff. It will be received by all devices on the LAN, but only the device with the specified IP address will reply.
The ARP resolution process does take a second or two to complete if no mapping for the destination devices IP address to MAC address is found in the ARP cache. For example, if the MAC address must be resolved through the ARP broadcast when pinging from one device to another, it can cause the first several echo requests to go unanswered, as shown on the output below. After this resolution has been completed, however, the second ping attempt should receive an answer to all five ICMP echo requests.
The sending host will not perform an ARP broadcast in its local subnet using the IP address of the destination host. A local ARP broadcast is only performed when the ANDing process deduces that the destination IP address is local. In this case, the destination is remote.
The destination host will not respond with its MAC address. The process of learning the MAC address of the destination computer is the responsibility of the local router interface on the subnet where the destination host resides.