The next dynamic addressing scheme is that used by most ISPs. They don't have enough addresses to be able to give a real Internet address to every subscriber. So, what they do is dynamically assign one to you when you sign on and put it back in the pool of unused numbers when you sign off. This is called Dynamic Host Configuration Protocol (DHCP). These all do essentially the same thing, although there are significant technical differences. When you sign on, you contact the terminal server at the ISP, who in your stead goes and gets an IP address for you. If you were to sign on from an Ethernet, you would send a broadcast message to all devices on your subnet asking the keeper of unused IP addresses to assign you one. In a large network, there are two ways to handle addressing. One is to permanently assign every device (host) an address. The other is to use DHCP. There are arguments for both approaches.

Address Resolution Protocol (ARP) is a little different. It is used by a router to find the physical address of a destination host when it has found the proper network. The router only has network-layer information in the packet. It needs to have a physical (Ethernet) address in order to actually deliver the packet. It uses the ARP to broadcast to all devices on the destination looking for that device whose IP address matches the one for...