|  | 9.6 | Who to ARP for?
| 9.6.2 | Example 1: the ARP request and reply
The example in Figure , host Cerf's IP address does not appear in host Stevens' ARP table. Host Stevens must send out an ARP request for the IP address 172.16.10.25, host Cerf's IP address. Once again, host Stevens knows it can do an ARP request directly for host Cerf, because it had determined that they are both on the same subnetwork. As also shown in Figure , the ARP request is encapsulated within an Ethernet frame. ARP request from host Stevens at 172.16.10.10 The ARP Request is a Layer 2 broadcast, which means there are all binary 1's in the destination MAC address. This is normally written in hexadecimal as all F's (FF-FF-FF-FF-FF-FF). The IP address Host Stevens is looking for is in the field Target IP Address. All hosts on the LAN receive and process this ARP Request because it is a Layer 2 broadcast. The hosts examine the Target IP Address to see if their IP address matches. ARP reply from host Cerf at 172.16.10.25 The host with the IP address that matched 172.16.10.25 will reply. This reply is unicast, meaning only the host that matches the MAC address will process it. Notice that in the ARP reply, the information in the "Sender" and "Target" fields is reversed from the ARP request. This is because the source is now host Cerf instead of host Stevens. Data Transmission from host Stevens Host Stevens receives the ARP reply and enters host Cerf's IP address and MAC address into its ARP Table. Host Stevens now encapsulates the IP packet into the Ethernet frame and sends the packet directly to host Cerf.