When we talk about IP services, we refer to the applications, protocols, and services that not only use IP themselves, but also provide data to be used by other IP protocols. | IP Services When we talk about IP services we refer to the applications protocols and services that not only use IP themselves but also provide data to be used by other IP protocols. These IP services typically allow for IP communications between hosts by performing functions such as physical address resolution automatic address assignment name resolution and time synchronization. Address Resolution Protocol ARP is an IP service that was developed to map physical addresses to logical addresses. This resolution is required because hosts need to be able to physically address the data frames at Layer 2 to the appropriate destination. In most cases the hosts only know each other by IP address. Consequently ARP functions by broadcasting on the local subnet for the host that has the IP address that needs to be resolved. Because it is a broadcast all hosts will process the packet but only the host that actually has that IP address will respond with its MAC address thereby allowing the original source to properly address the packet both logically by IP address and physically by MAC address. DHCP exists to provide unconfigured hosts on a network with the appropriate IP addressing information necessary to enable them to communicate on the network. Because a host that is a DHCP client does not have an IP address to use DHCP uses broadcasts between the DHCP client and the DHCP server. When a DHCP client is turned on it issues a broadcast known as a DHCP Discover packet. The objective of this broadcast is to discover whether there is a DHCP server on the network. If there is the DHCP server responds with a broadcast known as a DHCP Offer packet because the client still has no IP address. Because the packet is a broadcast the client still processes it even though the client has no configured IP address. If the network has multiple DHCP servers they all respond with a DHCP Offer and the client accepts the first offer it receives. The client then broadcasts a packet known as a .
