RFC 2131 (rfc2131) - Page 2 of 45
Dynamic Host Configuration Protocol
Alternative Format: Original Text Document
RFC 2131 Dynamic Host Configuration Protocol March 1997 4.1 Constructing and sending DHCP messages. . . . . . . . . . . . 22 4.2 DHCP server administrative controls . . . . . . . . . . . . . 25 4.3 DHCP server behavior. . . . . . . . . . . . . . . . . . . . . 26 4.4 DHCP client behavior. . . . . . . . . . . . . . . . . . . . . 34 5. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . .42 6. References . . . . . . . . . . . . . . . . . . . . . . . . . .42 7. Security Considerations. . . . . . . . . . . . . . . . . . . .43 8. Author's Address . . . . . . . . . . . . . . . . . . . . . . .44 A. Host Configuration Parameters . . . . . . . . . . . . . . . .45 List of Figures 1. Format of a DHCP message . . . . . . . . . . . . . . . . . . . 9 2. Format of the 'flags' field. . . . . . . . . . . . . . . . . . 11 3. Timeline diagram of messages exchanged between DHCP client and servers when allocating a new network address. . . . . . . . . 15 4. Timeline diagram of messages exchanged between DHCP client and servers when reusing a previously allocated network address. . 18 5. State-transition diagram for DHCP clients. . . . . . . . . . . 34 List of Tables 1. Description of fields in a DHCP message. . . . . . . . . . . . 10 2. DHCP messages. . . . . . . . . . . . . . . . . . . . . . . . . 14 3. Fields and options used by DHCP servers. . . . . . . . . . . . 28 4. Client messages from various states. . . . . . . . . . . . . . 33 5. Fields and options used by DHCP clients. . . . . . . . . . . . 37 1. Introduction The Dynamic Host Configuration Protocol (DHCP) provides configuration parameters to Internet hosts. DHCP consists of two components: a protocol for delivering host-specific configuration parameters from a DHCP server to a host and a mechanism for allocation of network addresses to hosts. DHCP is built on a client-server model, where designated DHCP server hosts allocate network addresses and deliver configuration parameters to dynamically configured hosts. Throughout the remainder of this document, the term "server" refers to a host providing initialization parameters through DHCP, and the term "client" refers to a host requesting initialization parameters from a DHCP server. A host should not act as a DHCP server unless explicitly configured to do so by a system administrator. The diversity of hardware and protocol implementations in the Internet would preclude reliable operation if random hosts were allowed to respond to DHCP requests. For example, IP requires the setting of many parameters within the protocol implementation software. Because IP can be used on many dissimilar kinds of network hardware, values for those parameters cannot be guessed or assumed to have correct defaults. Also, distributed address allocation schemes depend on a polling/defense Droms Standards Track
