get any dhcp package
get one from here
ftp://ftp.isc.org/isc/dhcp/dhcp-3.0.1.tar.gz
and look in the include dir. for dhcp structure
struct dhcp_packet {
u_int8_t op; /* 0: Message opcode/type */
u_int8_t htype; /* 1: Hardware addr type (net/if_types.h) */
u_int8_t hlen; /* 2: Hardware addr length */
u_int8_t hops; /* 3: Number of relay agent hops from client */
u_int32_t xid; /* 4: Transaction ID */
u_int16_t secs; /* 8: Seconds since client started looking */
u_int16_t flags; /* 10: Flag bits */
struct in_addr ciaddr; /* 12: Client IP address (if already in use) */
struct in_addr yiaddr; /* 16: Client IP address */
struct in_addr siaddr; /* 18: IP address of next server to talk to */
struct in_addr giaddr; /* 20: DHCP relay agent IP address */
unsigned char chaddr [16]; /* 24: Client hardware address */
char sname [DHCP_SNAME_LEN]; /* 40: Server name */
char file [DHCP_FILE_LEN]; /* 104: Boot filename */
unsigned char options [DHCP_OPTION_LEN];
/* 212: Optional parameters
(actual length dependent on MTU). */
};
regards