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Tweak some comments

/*	$OpenBSD: dhcp.h,v 1.21 2017/07/24 16:17:35 krw Exp $	*/

/* Protocol structures. */

/*
 * Copyright (c) 1995, 1996 The Internet Software Consortium.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of The Internet Software Consortium nor the names
 *    of its contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * This software has been written for the Internet Software Consortium
 * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
 * Enterprises.  To learn more about the Internet Software Consortium,
 * see ``http://www.vix.com/isc''.  To learn more about Vixie
 * Enterprises, see ``http://www.vix.com''.
 */

#define DHCP_UDP_OVERHEAD	(20 + /* IP header */		\
				 8)   /* UDP header */
#define DHCP_SNAME_LEN		64
#define DHCP_FILE_LEN		128
#define DHCP_FIXED_NON_UDP	236
#define DHCP_FIXED_LEN		(DHCP_FIXED_NON_UDP + DHCP_UDP_OVERHEAD)
						/* Everything but options. */
#define DHCP_MTU_MAX		1500
#define DHCP_OPTION_LEN		(DHCP_MTU_MAX - DHCP_FIXED_LEN)

/* Respect historical limits on 'search' line in resolv.conf(5) */
#define DHCP_DOMAIN_SEARCH_LEN	1024
#define DHCP_DOMAIN_SEARCH_CNT	6

#define BOOTP_MIN_LEN		300

struct dhcp_packet {
	uint8_t		op;	/* Message opcode/type */
	uint8_t		htype;	/* Hardware addr type (see net/if_types.h) */
	uint8_t		hlen;	/* Hardware addr length */
	uint8_t		hops;	/* Number of relay agent hops from client */
	uint32_t	xid;	/* Transaction ID */
	uint16_t	secs;	/* Seconds since client started looking */
	uint16_t	flags;	/* Flag bits */
	struct in_addr	ciaddr;	/* Client IP address (if already in use) */
	struct in_addr	yiaddr;	/* Client IP address */
	struct in_addr	siaddr;	/* IP address of next server to talk to */
	struct in_addr	giaddr;	/* DHCP relay agent IP address */
	unsigned char	chaddr[16];		/* Client hardware address */
	char		sname[DHCP_SNAME_LEN];	/* Server name */
	char		file[DHCP_FILE_LEN];	/* Boot filename */
	unsigned char	options[DHCP_OPTION_LEN];
				/* Optional parameters
				   (actual length dependent on MTU). */
};

/* BOOTP (rfc951) message types */
#define BOOTREQUEST	1
#define BOOTREPLY	2

/* Possible values for flags field. */
#define BOOTP_BROADCAST 32768L

/* Possible values for hardware type (htype) field. */
#define HTYPE_ETHER		1	/* Ethernet			*/
#define HTYPE_IPSEC_TUNNEL	31	/* IPsec Tunnel (RFC3456)	*/

/*
 * Magic cookie validating dhcp options field (and bootp vendor
 * extensions field).
 */
#define DHCP_OPTIONS_COOKIE		"\143\202\123\143"
#define DHCP_OPTIONS_COOKIE_LEN		4
#define DHCP_OPTIONS_MESSAGE_TYPE	"\065\001\000"

/* DHCP Option codes: */
#define DHO_PAD				0
#define DHO_SUBNET_MASK			1
#define DHO_TIME_OFFSET			2
#define DHO_ROUTERS			3
#define DHO_TIME_SERVERS		4
#define DHO_NAME_SERVERS		5
#define DHO_DOMAIN_NAME_SERVERS		6
#define DHO_LOG_SERVERS			7
#define DHO_COOKIE_SERVERS		8
#define DHO_LPR_SERVERS			9
#define DHO_IMPRESS_SERVERS		10
#define DHO_RESOURCE_LOCATION_SERVERS	11
#define DHO_HOST_NAME			12
#define DHO_BOOT_SIZE			13
#define DHO_MERIT_DUMP			14
#define DHO_DOMAIN_NAME			15
#define DHO_SWAP_SERVER			16
#define DHO_ROOT_PATH			17
#define DHO_EXTENSIONS_PATH		18
#define DHO_IP_FORWARDING		19
#define DHO_NON_LOCAL_SOURCE_ROUTING	20
#define DHO_POLICY_FILTER		21
#define DHO_MAX_DGRAM_REASSEMBLY	22
#define DHO_DEFAULT_IP_TTL		23
#define DHO_PATH_MTU_AGING_TIMEOUT	24
#define DHO_PATH_MTU_PLATEAU_TABLE	25
#define DHO_INTERFACE_MTU		26
#define DHO_ALL_SUBNETS_LOCAL		27
#define DHO_BROADCAST_ADDRESS		28
#define DHO_PERFORM_MASK_DISCOVERY	29
#define DHO_MASK_SUPPLIER		30
#define DHO_ROUTER_DISCOVERY		31
#define DHO_ROUTER_SOLICITATION_ADDRESS	32
#define DHO_STATIC_ROUTES		33
#define DHO_TRAILER_ENCAPSULATION	34
#define DHO_ARP_CACHE_TIMEOUT		35
#define DHO_IEEE802_3_ENCAPSULATION	36
#define DHO_DEFAULT_TCP_TTL		37
#define DHO_TCP_KEEPALIVE_INTERVAL	38
#define DHO_TCP_KEEPALIVE_GARBAGE	39
#define DHO_NIS_DOMAIN			40
#define DHO_NIS_SERVERS			41
#define DHO_NTP_SERVERS			42
#define DHO_VENDOR_ENCAPSULATED_OPTIONS	43
#define DHO_NETBIOS_NAME_SERVERS	44
#define DHO_NETBIOS_DD_SERVER		45
#define DHO_NETBIOS_NODE_TYPE		46
#define DHO_NETBIOS_SCOPE		47
#define DHO_FONT_SERVERS		48
#define DHO_X_DISPLAY_MANAGER		49
#define DHO_DHCP_REQUESTED_ADDRESS	50
#define DHO_DHCP_LEASE_TIME		51
#define DHO_DHCP_OPTION_OVERLOAD	52
#define DHO_DHCP_MESSAGE_TYPE		53
#define DHO_DHCP_SERVER_IDENTIFIER	54
#define DHO_DHCP_PARAMETER_REQUEST_LIST	55
#define DHO_DHCP_MESSAGE		56
#define DHO_DHCP_MAX_MESSAGE_SIZE	57
#define DHO_DHCP_RENEWAL_TIME		58
#define DHO_DHCP_REBINDING_TIME		59
#define DHO_DHCP_CLASS_IDENTIFIER	60
#define DHO_DHCP_CLIENT_IDENTIFIER	61
#define DHO_NISPLUS_DOMAIN		64
#define DHO_NISPLUS_SERVERS		65
#define DHO_TFTP_SERVER			66
#define DHO_BOOTFILE_NAME		67
#define DHO_MOBILE_IP_HOME_AGENT	68
#define DHO_SMTP_SERVER			69
#define DHO_POP_SERVER			70
#define DHO_NNTP_SERVER			71
#define DHO_WWW_SERVER			72
#define DHO_FINGER_SERVER		73
#define DHO_IRC_SERVER			74
#define DHO_STREETTALK_SERVER		75
#define DHO_STREETTALK_DIRECTORY_ASSISTANCE_SERVER	76
#define DHO_DHCP_USER_CLASS_ID		77
#define DHO_RELAY_AGENT_INFORMATION	82
#define DHO_NDS_SERVERS			85
#define DHO_NDS_TREE_NAME		86
#define DHO_NDS_CONTEXT			87
#define	DHO_DOMAIN_SEARCH		119
#define DHO_CLASSLESS_STATIC_ROUTES	121
#define DHO_TFTP_CONFIG_FILE		144
#define DHO_VOIP_CONFIGURATION_SERVER	150
#define DHO_CLASSLESS_MS_STATIC_ROUTES	249
#define DHO_AUTOPROXY_SCRIPT		252
#define DHO_END				255
#define DHO_COUNT			256	/* # of DHCP options */

/* DHCP message types. */
#define DHCPDISCOVER	1
#define DHCPOFFER	2
#define DHCPREQUEST	3
#define DHCPDECLINE	4
#define DHCPACK		5
#define DHCPNAK		6
#define DHCPRELEASE	7
#define DHCPINFORM	8

/* Relay Agent Information sub-options */
#define RAI_CIRCUIT_ID	1
#define RAI_REMOTE_ID	2
#define RAI_AGENT_ID	3