|  | 8.6 | TCP/IP Fundamentals
| 8.6.2 | DHCP, DNS, WINS, and host files

DHCP The Dynamic Host Configuration Protocol (DHCP) automatically distributes IP addresses to devices which are connected to the network. When a client tries to connect to the network, a request is sent to the DHCP server for configuration settings. Once the server receives the message, the DHCP server sends a reply to the client, which includes the configuration information, then keeps a record of the addresses that have been assigned. DHCP uses the BOOTP protocol to communicate with clients. Clients must renew their IP addresses after 50% of the address lease life, and again at 87.5% of the lease life, by sending a DHCPREQUEST message. Client hosts keep their IP address until their lease expires or they send a DHCPRELEASE command. IPCONFIG and WINIPCFG are utilities run from the command line that allow verification of the IP Address information that has been assigned to the client host. DNS Domain Name Services (DNS) is a name resolution service that resolves (associates) host names to IP addresses. DNS keeps a record of IP addresses and hosts names in a process called a domain. DNS provides services along a hierarchical chain, with a database design similar to a file tree structure (root-level/top-level/second-level/host name). DNS also services requests for host names that can not be resolved locally. Large internetworks have several levels of DNS servers to provide efficient name resolution. WINS Windows Internet Naming Service (WINS) works as DNS does to resolve IP addresses with host names. However, a difference between DNS and WINS; WINS uses a flat namespace by using NetBios, instead of using a hierarchical one like DNS. To resolve an IP address, a WINS client host registers its NetBIOS and IP addresses with the WINS server. Then the WINS client host sends a name query request to the WINS server, indicating that it desires to transmit to another host. If the desired IP address and host name are found in the server's WINS registry, then they will be sent to original WINS client host. Requests made by WINS are routable. The WINS proxy agent is used for non-WINS clients such as UNIX hosts; however, WINS does not provide support for Macintosh OS's. HOSTS Files HOSTS file - statically configured host name to IP address translation. This file is usable in all hosts' IP protocol stacks. If present it will be referenced for name resolution before an external DNS search. LMHOSTS provides the same services in a WINS environment and is statically configured on Windows networking clients.