text: /*
   *  libnet
   *  libnet-functions.h - function prototypes
   *
   *  Copyright (c) 1998 - 2004 Mike D. Schiffman <mike@infonexus.com>
   *  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.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
   *
   */
  
  #ifndef __LIBNET_FUNCTIONS_H
  #define __LIBNET_FUNCTIONS_H
  /**
   * @file libnet-functions.h
   * @brief libnet exported function prototypes
   */
  
  /**
   * Creates the libnet environment. It initializes the library and returns a 
   * libnet context. If the injection_type is LIBNET_LINK or LIBNET_LINK_ADV, the
   * function initializes the injection primitives for the link-layer interface
   * enabling the application programmer to build packets starting at the
   * data-link layer (which also provides more granular control over the IP
   * layer). If libnet uses the link-layer and the device argument is non-NULL,
   * the function attempts to use the specified network device for packet
   * injection. This is either a canonical string that references the device
   * (such as "eth0" for a 100MB Ethernet card on Linux or "fxp0" for a 100MB
   * Ethernet card on OpenBSD) or the dots and decimals representation of the
   * device's IP address (192.168.0.1). If device is NULL, libnet attempts to
   * find a suitable device to use. If the injection_type is LIBNET_RAW4 or
   * LIBNET_RAW4_ADV, the function initializes the injection primitives for the
   * IPv4 raw socket interface. The final argument, err_buf, should be a buffer
   * of size LIBNET_ERRBUF_SIZE and holds an error message if the function fails.
   * This function requires root privileges to execute successfully. Upon
   * success, the function returns a valid libnet context for use in later
   * function calls; upon failure, the function returns NULL.
   * @param injection_type packet injection type (LIBNET_LINK, LIBNET_LINK_ADV, LIBNET_RAW4, LIBNET_RAW4_ADV, LIBNET_RAW6, LIBNET_RAW6_ADV)
   * @param device the interface to use (NULL and libnet will choose one)
   * @param err_buf will contain an error message on failure
   * @return libnet context ready for use or NULL on error.
   */
  LIBNET_API
  libnet_t *
  libnet_init(int injection_type, const char *device, char *err_buf);
  
  /**
   * Shuts down the libnet session referenced by l. It closes the network 
   * interface and frees all internal memory structures associated with l.  
   * @param l pointer to a libnet context
   */
  LIBNET_API
  void
  libnet_destroy(libnet_t *l);
  
  /**
   * Clears the current packet referenced and frees all pblocks. Should be
   * called when the programmer want to send a completely new packet of
   * a different type using the same context.
   * @param l pointer to a libnet context
   */
  LIBNET_API
  void
  libnet_clear_packet(libnet_t *l);
  
  /**
   * Fills in a libnet_stats structure with packet injection statistics
   * (packets written, bytes written, packet sending errors).
   * @param l pointer to a libnet context
   * @param ls pointer to a libnet statistics structure
   */
  LIBNET_API
  void
  libnet_stats(libnet_t *l, struct libnet_stats *ls);
  
  /**
   * Returns the FILENO of the file descriptor used for packet injection.
   * @param l pointer to a libnet context
   * @return the file number of the file descriptor used for packet injection
   */
  LIBNET_API
  int 
  libnet_getfd(libnet_t *l);
  
  /**
   * Returns the canonical name of the device used for packet injection.
   * @param l pointer to a libnet context
   * @return the canonical name of the device used for packet injection. Note 
   * it can be NULL without being an error.
   */
  LIBNET_API
  const char *
  libnet_getdevice(libnet_t *l);
  
  /**
   * Returns the pblock buffer contents for the specified ptag; a
   * subsequent call to libnet_getpbuf_size() should be made to determine the
   * size of the buffer.
   * @param l pointer to a libnet context
   * @param ptag the ptag reference number
   * @return a pointer to the pblock buffer or NULL on error
   */
  LIBNET_API
  uint8_t *
  libnet_getpbuf(libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Returns the pblock buffer size for the specified ptag; a
   * previous call to libnet_getpbuf() should be made to pull the actual buffer
   * contents.
   * @param l pointer to a libnet context
   * @param ptag the ptag reference number
   * @return the size of the pblock buffer
   */ 
  LIBNET_API
  uint32_t
  libnet_getpbuf_size(libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Returns the last error set inside of the referenced libnet context. This
   * function should be called anytime a function fails or an error condition
   * is detected inside of libnet.
   * @param l pointer to a libnet context
   * @return an error string or NULL if no error has occurred
   */ 
  LIBNET_API
  char *
  libnet_geterror(libnet_t *l);
  
  /**
   * Returns the sum of the size of all of the pblocks inside of l (this should
   * be the resulting packet size).
   * @param l pointer to a libnet context
   * @return the size of the packet in l
   */ 
  LIBNET_API
  uint32_t
  libnet_getpacket_size(libnet_t *l);
  
  /**
   * Seeds the pseudo-random number generator.
   * @param l pointer to a libnet context
   * @retval 1 on success
   * @retval -1 on failure
   */
  LIBNET_API
  int
  libnet_seed_prand(libnet_t *l);
  
  /**
   * Generates an unsigned pseudo-random value within the range specified by
   * mod.
   * LIBNET_PR2    0 - 1
   * LIBNET_PR8    0 - 255
   * LIBNET_PR16   0 - 32767
   * LIBNET_PRu16  0 - 65535
   * LIBNET_PR32   0 - 2147483647
   * LIBNET_PRu32  0 - 4294967295
   *
   * @param mod one the of LIBNET_PR* constants
   * @retval 1 on success
   * @retval -1 on failure
   */
  LIBNET_API
  uint32_t
  libnet_get_prand(int mod);
  
  /**
   * If a given protocol header is built with the checksum field set to "0", by
   * default libnet will calculate the header checksum prior to injection. If the
   * header is set to any other value, by default libnet will not calculate the
   * header checksum. To over-ride this behavior, use libnet_toggle_checksum().
   * Switches auto-checksumming on or off for the specified ptag. If mode is set
   * to LIBNET_ON, libnet will mark the specified ptag to calculate a checksum 
   * for the ptag prior to injection. This assumes that the ptag refers to a 
   * protocol that has a checksum field. If mode is set to LIBNET_OFF, libnet
   * will clear the checksum flag and no checksum will be computed prior to 
   * injection. This assumes that the programmer will assign a value (zero or
   * otherwise) to the checksum field.  Often times this is useful if a
   * precomputed checksum or some other predefined value is going to be used.
   * Note that when libnet is initialized with LIBNET_RAW4, the IPv4 header
   * checksum will always be computed by the kernel prior to injection, 
   * regardless of what the programmer sets.
   * @param l pointer to a libnet context
   * @param ptag the ptag reference number
   * @param mode LIBNET_ON or LIBNET_OFF
   * @retval 1 on success
   * @retval -1 on failure
   */
  LIBNET_API
  int
  libnet_toggle_checksum(libnet_t *l, libnet_ptag_t ptag, int mode);
  
  /**
   * Takes a network byte ordered IPv4 address and returns a pointer to either a 
   * canonical DNS name (if it has one) or a string of dotted decimals. This may
   * incur a DNS lookup if the hostname and mode is set to LIBNET_RESOLVE. If
   * mode is set to LIBNET_DONT_RESOLVE, no DNS lookup will be performed and
   * the function will return a pointer to a dotted decimal string. The function
   * cannot fail -- if no canonical name exists, it will fall back on returning
   * a dotted decimal string. This function is non-reentrant.
   * @param in network byte ordered IPv4 address
   * @param use_name LIBNET_RESOLVE or LIBNET_DONT_RESOLVE
   * @return a pointer to presentation format string
   */
  LIBNET_API
  char *
  libnet_addr2name4(uint32_t in, uint8_t use_name);
  
  /**
   * Takes a dotted decimal string or a canonical DNS name and returns a 
   * network byte ordered IPv4 address. This may incur a DNS lookup if mode is
   * set to LIBNET_RESOLVE and host_name refers to a canonical DNS name. If mode
   * is set to LIBNET_DONT_RESOLVE no DNS lookup will occur. The function can
   * fail if DNS lookup fails or if mode is set to LIBNET_DONT_RESOLVE and
   * host_name refers to a canonical DNS name.
   * @param l pointer to a libnet context
   * @param host_name pointer to a string containing a presentation format host
   * name
   * @param use_name LIBNET_RESOLVE or LIBNET_DONT_RESOLVE
   * @return address in network byte order
   * @retval -1 (2^32 - 1) on error 
   */
  LIBNET_API
  uint32_t
  libnet_name2addr4(libnet_t *l, const char *host_name, uint8_t use_name);
  
  extern const struct libnet_in6_addr in6addr_error;
  
  /**
   * Check a libnet_in6_addr structure for identity with in6addr_error.
   * @param addr address to check
   * @retval 1 if addr is in6addr_error
   * @retval 0 if it is not
   */
  LIBNET_API
  int
  libnet_in6_is_error(struct libnet_in6_addr addr);
  
  /**
   * Takes a dotted decimal string or a canonical DNS name and returns a 
   * network byte ordered IPv6 address. This may incur a DNS lookup if mode is
   * set to LIBNET_RESOLVE and host_name refers to a canonical DNS name. If mode
   * is set to LIBNET_DONT_RESOLVE no DNS lookup will occur. The function can
   * fail if DNS lookup fails or if mode is set to LIBNET_DONT_RESOLVE and
   * host_name refers to a canonical DNS name.
   * @param l pointer to a libnet context
   * @param host_name pointer to a string containing a presentation format host
   * name
   * @param use_name LIBNET_RESOLVE or LIBNET_DONT_RESOLVE
   * @return network byte ordered IPv6 address structure 
   */
  LIBNET_API
  struct libnet_in6_addr
  libnet_name2addr6(libnet_t *l, const char *host_name, uint8_t use_name);
  
  /**
   * Should document this baby right here.
   */
  LIBNET_API
  void
  libnet_addr2name6_r(struct libnet_in6_addr addr, uint8_t use_name,
  char *host_name, int host_name_len);
  
  /**
   * Creates a new port list. Port list chains are useful for TCP and UDP-based
   * applications that need to send packets to a range of ports (contiguous or
   * otherwise). The port list chain, which token_list points to, should contain
   * a series of int8_tacters from the following list: "0123456789,-" of the
   * general format "x - y, z", where "xyz" are port numbers between 0 and 
   * 65,535. plist points to the front of the port list chain list for use in 
   * further libnet_plist_chain() functions. Upon success, the function returns
   * 1. Upon failure, the function returns -1 and libnet_geterror() can tell you
   * why.
   * @param l pointer to a libnet context
   * @param plist if successful, will refer to the portlist, if not, NULL
   * @param token_list string containing the port list primitive
   * @retval 1 on success
   * @retval -1 on failure
   */
  LIBNET_API
  int
  libnet_plist_chain_new(libnet_t *l, libnet_plist_t **plist, char *token_list);
  
  /**
   * Returns the next port list chain pair from the port list chain plist. bport
   * and eport contain the starting port number and ending port number, 
   * respectively. Upon success, the function returns 1 and fills in the port
   * variables; however, if the list is empty, the function returns 0 and sets 
   * both port variables to 0. Upon failure, the function returns -1.
   * @param plist previously created portlist
   * @param bport will contain the beginning port number or 0
   * @param eport will contain the ending port number or 0
   * @retval 1 on success
   * @retval 0 if empty
   * @retval -1 on failure
   */
  LIBNET_API
  int
  libnet_plist_chain_next_pair(libnet_plist_t *plist, uint16_t *bport, 
  uint16_t *eport); 
  
  /**
   * Runs through the port list and prints the contents of the port list chain
   * list to stdout.
   * @param plist previously created portlist
   * @retval 1 on success
   * @retval -1 on failure
   */
  LIBNET_API
  int
  libnet_plist_chain_dump(libnet_plist_t *plist);
  
  /**
   * Runs through the port list and prints the contents of the port list chain
   * list to string. This function uses strdup and is not re-entrant.  It also
   * has a memory leak and should not really be used.
   * @param plist previously created portlist
   * @return a printable string containing the port list contents on success or NULL on error
   */
  LIBNET_API
  char *
  libnet_plist_chain_dump_string(libnet_plist_t *plist);
  
  /**
   * Frees all memory associated with port list chain.
   * @param plist previously created portlist
   * @retval 1 on success
   * @retval -1 on failure
   */
  LIBNET_API
  int
  libnet_plist_chain_free(libnet_plist_t *plist);
  
  /**
   * @section PBF Packet Builder Functions
   *
   * The core of libnet is the platform-independent packet-building 
   * functionality. These functions enable an application programmer to build 
   * protocol headers (and data) in a simple and consistent manner without having
   * to worry (too much) about low-level network odds and ends. Each 
   * libnet_build() function builds a piece of a packet (generally a protocol 
   * header). While it is perfectly possible to build an entire, 
   * ready-to-transmit packet with a single call to a libnet_build() function, 
   * generally more than one builder-class function call is required to construct
   * a full packet. A complete wire-ready packet generally consists of more than 
   * one piece.
   * Every function that builds a protocol header takes a series of arguments 
   * roughly corresponding to the header values as they appear on the wire. This 
   * process is intuitive but often makes for functions with huge prototypes and 
   * large stack frames.
   * One important thing to note is that you must call these functions in order, 
   * corresponding to how they should appear on the wire (from the highest 
   * protocol layer on down). This building process is intuitive; it approximates
   * what happens in an operating system kernel. In other words, to build a 
   * Network Time Protocol (NTP) packet by using the link-layer interface, the 
   * application programmer would call the libnet_build() functions in the 
   * following order:
   * 1. libnet_build_ntp()
   * 2. libnet_build_udp()
   * 3. libnet_build_ipv4()
   * 4. libnet_build_ethernet()
   * This ordering is essential for libnet 1.1.x to properly link together the 
   * packet internally (previous libnet versions did not have the requirement).
   *
   * @subsection TPI The Payload Interface
   *
   * The payload interface specifies an optional way to include data directly 
   * after the protocol header in question. You can use this function for a 
   * variety of purposes, including the following:
   * - Including additional or arbitrary protocol header information that is not 
   *   available from a libnet interface
   * - Including a packet payload (data segment)
   * - Building another protocol header that is not available from a libnet 
   *   interface
   * To employ the interface, the application programmer should construct the i
   * payload data and pass a const uint8_t * to this data and its size to the desired
   * libnet_build() function. Libnet handles the rest.
   *
   * It is important to note that some functions (notably the IPv6 builders) do
   * use the payload interface to specify variable length but ostensibly 
   * non-optional data. See the individual libnet_build_ipv6*() functions for
   * more information.
   * 
   * @subsection PT Protocol Tags and Packet Builder Return Values
   *
   * Libnet uses the protocol tag (ptag) to identify individual pieces of a 
   * packet after being created. A new ptag results every time a libnet_build() 
   * function with an empty (0) ptag argument completes successfully. This new 
   * ptag now refers to the packet piece just created. The application 
   * programmer's responsibility is to save this value if he or she plans to 
   * modify this particular portion later on in the program. If the application 
   * programmer needs to modify some portion of that particular packet piece 
   * again, he or she calls the same libnet_build() function specifying the 
   * saved ptag argument. Libnet then searches for that packet piece and modifies
   * it rather than creating a new one. Upon failure for any reason, 
   * libnet_build() functions return -1; libnet_geterror() tells you why.
   */
  
  /**
   * Builds an IEEE 802.1q VLAN tagging header. Depending on the value of
   * len_proto, the function wraps the 802.1q header inside either an IEEE 802.3
   * header or an RFC 894 Ethernet II (DIX) header (both resulting in an 18-byte
   * frame). If len is 1500 or less, most receiving protocol stacks parse the
   * frame as an IEEE 802.3 encapsulated frame. If len is one of the Ethernet type
   * values, most protocol stacks parse the frame as an RFC 894 Ethernet II
   * encapsulated frame. Note the length value is calculated without the 802.1q
   * header of 18 bytes.
   * @param dst pointer to a six byte source ethernet address
   * @param src pointer to a six byte destination ethernet address
   * @param tpi tag protocol identifier
   * @param priority priority
   * @param cfi canonical format indicator
   * @param vlan_id vlan identifier
   * @param len_proto length (802.3) protocol (Ethernet II) 
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_802_1q(const uint8_t *dst, const uint8_t *src, uint16_t tpi,
  uint8_t priority, uint8_t cfi, uint16_t vlan_id, uint16_t len_proto,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IEEE 802.1x extended authentication protocol header.
   * @param eap_ver the EAP version
   * @param eap_type the EAP type
   * @param length frame length
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_802_1x(uint8_t eap_ver, uint8_t eap_type, uint16_t length, 
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IEEE 802.2 LLC header.
   * @param dsap destination service access point
   * @param ssap source service access point
   * @param control control field
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_802_2(uint8_t dsap, uint8_t ssap, uint8_t control,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IEEE 802.2 LLC SNAP header.
   * @param dsap destination service access point
   * @param ssap source service access point
   * @param control control field
   * @param oui Organizationally Unique Identifier
   * @param type upper layer protocol
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_802_2snap(uint8_t dsap, uint8_t ssap, uint8_t control, 
  uint8_t *oui, uint16_t type, const uint8_t* payload, uint32_t payload_s,
  libnet_t *l, libnet_ptag_t ptag); 
  
  /**
   * Builds an IEEE 802.3 header. The 802.3 header is almost identical to the 
   * RFC 894 Ethernet II header, the exception being that the field immediately
   * following the source address holds the frame's length (as opposed to the
   * layer 3 protocol). You should only use this function when libnet is
   * initialized with the LIBNET_LINK interface.
   * @param dst destination ethernet address
   * @param src source ethernet address
   * @param len frame length sans header
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_802_3(const uint8_t *dst, const uint8_t *src, uint16_t len, 
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an Ethernet header. The RFC 894 Ethernet II header is almost 
   * identical to the IEEE 802.3 header, with the exception that the field 
   * immediately following the source address holds the layer 3 protocol (as
   * opposed to frame's length). You should only use this function when 
   * libnet is initialized with the LIBNET_LINK interface. 
   * @param dst destination ethernet address
   * @param src source ethernet address
   * @param type upper layer protocol type
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ethernet(const uint8_t *dst, const uint8_t *src, uint16_t type, 
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Autobuilds an Ethernet header. The RFC 894 Ethernet II header is almost 
   * identical to the IEEE 802.3 header, with the exception that the field 
   * immediately following the source address holds the layer 3 protocol (as
   * opposed to frame's length). You should only use this function when 
   * libnet is initialized with the LIBNET_LINK interface. 
   * @param dst destination ethernet address
   * @param type upper layer protocol type
   * @param l pointer to a libnet context
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_autobuild_ethernet(const uint8_t *dst, uint16_t type, libnet_t *l);
  
  /**
   * Builds a Fiber Distributed Data Interface (FDDI) header.
   * @param fc class format and priority
   * @param dst destination fddi address
   * @param src source fddi address
   * @param dsap destination service access point
   * @param ssap source service access point
   * @param cf cf
   * @param oui 3 byte IEEE organizational code
   * @param type upper layer protocol 
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_fddi(uint8_t fc, const uint8_t *dst, const uint8_t *src, uint8_t dsap,
  uint8_t ssap, uint8_t cf, const uint8_t *oui, uint16_t type, const uint8_t* payload,
  uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Autobuilds a Fiber Distributed Data Interface (FDDI) header.
   * @param fc class format and priority
   * @param dst destination fddi address
   * @param dsap destination service access point
   * @param ssap source service access point
   * @param cf cf
   * @param oui IEEE organizational code
   * @param type upper layer protocol 
   * @param l pointer to a libnet context
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_autobuild_fddi(uint8_t fc, const uint8_t *dst, uint8_t dsap, uint8_t ssap,
  uint8_t cf, const uint8_t *oui, uint16_t type, libnet_t *l);
  
  /**
   * Builds an Address Resolution Protocol (ARP) header.  Depending on the op
   * value, the function builds one of several different types of RFC 826 or
   * RFC 903 RARP packets.
   * @param hrd hardware address format
   * @param pro protocol address format
   * @param hln hardware address length
   * @param pln protocol address length
   * @param op ARP operation type
   * @param sha sender's hardware address
   * @param spa sender's protocol address
   * @param tha target hardware address
   * @param tpa target protocol address
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_arp(uint16_t hrd, uint16_t pro, uint8_t hln, uint8_t pln,
  uint16_t op, const uint8_t *sha, const uint8_t *spa, const uint8_t *tha, const uint8_t *tpa,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Autouilds an Address Resolution Protocol (ARP) header.  Depending on the op
   * value, the function builds one of several different types of RFC 826 or
   * RFC 903 RARP packets.
   * @param op ARP operation type
   * @param sha sender's hardware address
   * @param spa sender's protocol address
   * @param tha target hardware address
   * @param tpa target protocol address
   * @param l pointer to a libnet context
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_autobuild_arp(uint16_t op, const uint8_t *sha, const uint8_t *spa, const uint8_t *tha,
  const uint8_t *tpa, libnet_t *l);
  
  /**
   * Builds an RFC 793 Transmission Control Protocol (TCP) header.
   * @param sp source port
   * @param dp destination port
   * @param seq sequence number
   * @param ack acknowledgement number
   * @param control control flags
   * @param win window size
   * @param sum checksum (0 for libnet to auto-fill)
   * @param urg urgent pointer
   * @param len total length of the TCP packet (for checksum calculation)
   * @param payload
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_tcp(uint16_t sp, uint16_t dp, uint32_t seq, uint32_t ack,
  uint8_t control, uint16_t win, uint16_t sum, uint16_t urg, uint16_t len, 
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an RFC 793 Transmission Control Protocol (TCP) options header.
   * The function expects options to be a valid TCP options string of size 
   * options_s, which is no larger than 40 bytes (the maximum size of an 
   * options string). The function checks to ensure that the packet consists of 
   * a TCP header preceded by an IPv4 header, and that the addition of the
   * options string would not result in a packet larger than 65,535 bytes
   * (IPMAXPACKET). The function counts up the number of 32-bit words in the
   * options string and adjusts the TCP header length value as necessary.
   * @param options byte string of TCP options
   * @param options_s length of options string
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_tcp_options(const uint8_t *options, uint32_t options_s, libnet_t *l,
  libnet_ptag_t ptag);
  
  /**
   * Builds an RFC 768 User Datagram Protocol (UDP) header.
   * @param sp source port
   * @param dp destination port
   * @param len total length of the UDP packet
   * @param sum checksum (0 for libnet to auto-fill)
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_udp(uint16_t sp, uint16_t dp, uint16_t len, uint16_t sum,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds a Cisco Discovery Protocol (CDP) header. Cisco Systems designed CDP
   * to aid in the network management of adjacent Cisco devices. The CDP protocol
   * specifies data by using a type/length/value (TLV) setup. The first TLV can
   * specified by using the functions type, length, and value arguments. To
   * specify additional TLVs, the programmer could either use the payload 
   * interface or libnet_build_data() to construct them.
   * @param version CDP version
   * @param ttl time to live (time information should be cached by recipient)
   * @param sum checksum (0 for libnet to auto-fill)
   * @param type type of data contained in value
   * @param value_s length of value argument
   * @param value the CDP information string
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_cdp(uint8_t version, uint8_t ttl, uint16_t sum, uint16_t type,
  uint16_t value_s, const uint8_t *value, const uint8_t* payload, uint32_t payload_s,
  libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IP version 4 RFC 792 Internet Control Message Protocol (ICMP)
   * echo request/reply header
   * @param type type of ICMP packet (should be ICMP_ECHOREPLY or ICMP_ECHO)
   * @param code code of ICMP packet (should be 0)
   * @param sum checksum (0 for libnet to auto-fill)
   * @param id identification number
   * @param seq packet sequence number
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_icmpv4_echo(uint8_t type, uint8_t code, uint16_t sum,
  uint16_t id, uint16_t seq, const uint8_t* payload, uint32_t payload_s,
  libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IP version 4 RFC 792 Internet Control Message Protocol (ICMP)
   * IP netmask request/reply header.
   * @param type type of ICMP packet (should be ICMP_MASKREQ or ICMP_MASKREPLY)
   * @param code code of ICMP packet (should be 0)
   * @param sum checksum (0 for libnet to auto-fill)
   * @param id identification number
   * @param seq packet sequence number
   * @param mask subnet mask
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_icmpv4_mask(uint8_t type, uint8_t code, uint16_t sum,
  uint16_t id, uint16_t seq, uint32_t mask, const uint8_t* payload,
  uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IP version 4 RFC 792 Internet Control Message Protocol (ICMP)
   * unreachable header. The IP header that caused the error message should be 
   * built by a previous call to libnet_build_ipv4().
   * @param type type of ICMP packet (should be ICMP_UNREACH)
   * @param code code of ICMP packet (should be one of the 16 unreachable codes)
   * @param sum checksum (0 for libnet to auto-fill)
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_icmpv4_unreach(uint8_t type, uint8_t code, uint16_t sum,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IP version 4 RFC 792 Internet Message Control Protocol (ICMP) 
   * redirect header.  The IP header that caused the error message should be 
   * built by a previous call to libnet_build_ipv4().
   * @param type type of ICMP packet (should be ICMP_REDIRECT)
   * @param code code of ICMP packet (should be one of the four redirect codes)
   * @param sum checksum (0 for libnet to auto-fill)
   * @param gateway
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_icmpv4_redirect(uint8_t type, uint8_t code, uint16_t sum,
  uint32_t gateway, const uint8_t* payload, uint32_t payload_s, libnet_t *l,
  libnet_ptag_t ptag);
  
  /**
   * Builds an IP version 4 RFC 792 Internet Control Message Protocol (ICMP) time
   * exceeded header.  The IP header that caused the error message should be 
   * built by a previous call to libnet_build_ipv4().
   * @param type type of ICMP packet (should be ICMP_TIMXCEED)
   * @param code code of ICMP packet (ICMP_TIMXCEED_INTRANS / ICMP_TIMXCEED_REASS)
   * @param sum checksum (0 for libnet to auto-fill)
   * @param payload optional payload or NULL
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_icmpv4_timeexceed(uint8_t type, uint8_t code, uint16_t sum,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IP version 4 RFC 792 Internet Control Message Protocol (ICMP)
   * timestamp request/reply header.
   * @param type type of ICMP packet (should be ICMP_TSTAMP or ICMP_TSTAMPREPLY)
   * @param code code of ICMP packet (should be 0)
   * @param sum checksum (0 for libnet to auto-fill)
   * @param id identification number
   * @param seq sequence number
   * @param otime originate timestamp
   * @param rtime receive timestamp
   * @param ttime transmit timestamp
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_icmpv4_timestamp(uint8_t type, uint8_t code, uint16_t sum,
  uint16_t id, uint16_t seq, uint32_t otime, uint32_t rtime, uint32_t ttime,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IP version 6 RFC 4443 Internet Control Message Protocol (ICMP)
   * echo or echo reply header.
   * @param type type of ICMP packet (should be ICMP6_ECHO_REQUEST or ICMP6_ECHO_REPLY)
   * @param code code of ICMP packet (should be zero)
   * @param sum checksum (0 for libnet to auto-fill)
   * @param id echo id number
   * @param seq echo sequence number
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t libnet_build_icmpv6_echo(uint8_t type, uint8_t code, uint16_t
          sum, uint16_t id, uint16_t seq, uint8_t *payload, uint32_t payload_s,
          libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IP version 6 RFC 4443 Internet Control Message Protocol (ICMP)
   * unreachable header. The IP header that caused the error message should be 
   * built by a previous call to libnet_build_ipv6().
   * @param type type of ICMP packet (should be ICMP6_DST_UNREACH)
   * @param code code of ICMP packet (should be one of the 5 ICMP6_DST_UNREACH_* codes)
   * @param sum checksum (0 for libnet to auto-fill)
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_icmpv6_unreach(uint8_t type, uint8_t code, uint16_t sum,
  uint8_t *payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IP version 6 RFC 2461 Internet Control Message Protocol (ICMP)
   * NDP neighbour solicitation header. Could be used with
   * libnet_build_icmpv6_ndp_opt() and ICMPV6_NDP_OPT_SLLA.
   * @param type type of ICMP packet (should be ND_NEIGHBOR_SOLICIT)
   * @param code code of ICMP packet (should be zero)
   * @param sum checksum (0 for libnet to auto-fill)
   * @param target target ipv6 address
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t libnet_build_icmpv6_ndp_nsol(uint8_t type, uint8_t code,
          uint16_t sum, struct libnet_in6_addr target, uint8_t *payload, uint32_t
          payload_s, libnet_t* l, libnet_ptag_t ptag);
  
  /**
   * Builds an IP version 6 RFC 2461 Internet Control Message Protocol (ICMP)
   * NDP neighbour advertisement header. Could be used with
   * libnet_build_icmpv6_ndp_opt() and ND_OPT_TARGET_LINKADDR.
   * @param type type of ICMP packet (should be ND_NEIGHBOR_ADVERT)
   * @param code code of ICMP packet (should be zero)
   * @param sum checksum (0 for libnet to auto-fill)
   * @param flags should be a bitwise or of any applicable ND_NA_FLAG_* flags
   * @param target target ipv6 address
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t libnet_build_icmpv6_ndp_nadv(uint8_t type, uint8_t code,
          uint16_t sum, uint32_t flags, struct libnet_in6_addr target, uint8_t
          *payload, uint32_t payload_s, libnet_t* l, libnet_ptag_t ptag);
  
  /**
   * Builds ICMPv6 NDP options.
   * @param type one of ND_OPT_* types
   * @param option option data
   * @param option_s size of option data (will be padded out to an 8-byte boundary)
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t libnet_build_icmpv6_ndp_opt(uint8_t type, uint8_t* option,
          uint32_t option_s, libnet_t* l, libnet_ptag_t ptag);
  
  /**
   * Builds an RFC 1112 Internet Group Membership Protocol (IGMP) header.
   * @param type packet type
   * @param reserved (should be 0 for IGMPv1)
   * @param sum checksum (0 for libnet to auto-fill)
   * @param ip IPv4 address (in standard/network byte order)
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   * 
   * @note 'reserved' was previously called 'code', which it is not, in any IGMP version.
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_igmp(uint8_t type, uint8_t reserved, uint16_t sum, uint32_t ip,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds a version 4 RFC 791 Internet Protocol (IP) header.
   *
   * @param ip_len total length of the IP packet including all subsequent data (subsequent
   *   data includes any IP options and IP options padding)
   * @param tos type of service bits
   * @param id IP identification number
   * @param frag fragmentation bits and offset
   * @param ttl time to live in the network
   * @param prot upper layer protocol
   * @param sum checksum (0 for libnet to auto-fill)
   * @param src source IPv4 address (little endian)
   * @param dst destination IPv4 address (little endian)
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t 
  libnet_build_ipv4(uint16_t ip_len, uint8_t tos, uint16_t id, uint16_t frag,
  uint8_t ttl, uint8_t prot, uint16_t sum, uint32_t src, uint32_t dst,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an version 4 Internet Protocol (IP) options header. The function 
   * expects options to be a valid IP options string of size options_s, no larger
   * than 40 bytes (the maximum size of an options string).
   *
   * When building a chain, the options must be built, then the IPv4 header.
   *
   * When updating a chain, if the block following the options is an IPv4 header,
   * it's total length and header length will be updated if the options block
   * size changes.
   *
   * @param options byte string of IP options (it will be padded up to be an integral
   *   multiple of 32-bit words).
   * @param options_s length of options string
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t 
  libnet_build_ipv4_options(const uint8_t *options, uint32_t options_s, libnet_t *l,
  libnet_ptag_t ptag);
  
  /**
   * Autobuilds a version 4 Internet Protocol (IP) header. The function is useful
   * to build an IP header quickly when you do not need a granular level of
   * control. The function takes the same len, prot, and dst arguments as 
   * libnet_build_ipv4(). The function does not accept a ptag argument, but it
   * does return a ptag. In other words, you can use it to build a new IP header
   * but not to modify an existing one.
   * @param len total length of the IP packet including all subsequent data
   * @param prot upper layer protocol
   * @param dst destination IPv4 address (little endian)
   * @param l pointer to a libnet context
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_autobuild_ipv4(uint16_t len, uint8_t prot, uint32_t dst, libnet_t *l);
  
  /**
   * Builds a version 6 RFC 2460 Internet Protocol (IP) header.
   * @param tc traffic class
   * @param fl flow label
   * @param len total length of the IP packet
   * @param nh next header
   * @param hl hop limit
   * @param src source IPv6 address
   * @param dst destination IPv6 address
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ipv6(uint8_t tc, uint32_t fl, uint16_t len, uint8_t nh,
  uint8_t hl, struct libnet_in6_addr src, struct libnet_in6_addr dst, 
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds a version 6 RFC 2460 Internet Protocol (IP) fragmentation header.
   * @param nh next header
   * @param reserved unused value... OR IS IT!
   * @param frag fragmentation bits (ala ipv4)
   * @param id packet identification
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ipv6_frag(uint8_t nh, uint8_t reserved, uint16_t frag,
  uint32_t id, const uint8_t* payload, uint32_t payload_s, libnet_t *l,
  libnet_ptag_t ptag);
  
  /**
   * Builds a version 6 RFC 2460 Internet Protocol (IP) routing header. This
   * function is special in that it uses the payload interface to include the 
   * "type-specific data"; that is the routing information. Most often this will
   * be a number of 128-bit IPv6 addresses. The application programmer will build
   * a byte string of IPv6 address and pass them to the function using the
   * payload interface.
   * @param nh next header
   * @param len length of the header in 8-byte octets not including the first 8 octets
   * @param rtype routing header type
   * @param segments number of routing segments that follow
   * @param payload optional payload of routing information
   * @param payload_s payload length
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ipv6_routing(uint8_t nh, uint8_t len, uint8_t rtype,
  uint8_t segments, const uint8_t* payload, uint32_t payload_s, libnet_t *l,
  libnet_ptag_t ptag);
  
  /**
   * Builds a version 6 RFC 2460 Internet Protocol (IP) destination options
   * header. This function is special in that it uses the payload interface to
   * include the options data. The application programmer will build an IPv6 
   * options byte string and pass it to the function using the payload interface.
   * @param nh next header
   * @param len length of the header in 8-byte octets not including the first 8 octets
   * @param payload options payload
   * @param payload_s payload length
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ipv6_destopts(uint8_t nh, uint8_t len, const uint8_t* payload,
  uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds a version 6 RFC 2460 Internet Protocol (IP) hop by hop options
   * header. This function is special in that it uses the payload interface to
   * include the options data. The application programmer will build an IPv6
   * hop by hop options byte string and pass it to the function using the payload
   * interface.
   * @param nh next header
   * @param len length of the header in 8-byte octets not including the first 8 octets
   * @param payload options payload
   * @param payload_s payload length
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ipv6_hbhopts(uint8_t nh, uint8_t len, const uint8_t* payload,
  uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Autobuilds a version 6 RFC 2460 Internet Protocol (IP) header. The function
   * is useful to build an IP header quickly when you do not need a granular
   * level of control. The function takes the same len, nh, and dst arguments
   * as libnet_build_ipv4(). The function does not accept a ptag argument, but it
   * does return a ptag. In other words, you can use it to build a new IP header
   * but not to modify an existing one.
   * This function requires libnet_get_ipaddr6(), which is not yet implemented
   * for Win32 platforms.
   * @param len length
   * @param nh next header
   * @param dst destination IPv6 address
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_autobuild_ipv6(uint16_t len, uint8_t nh, struct libnet_in6_addr dst,
  libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds a Cisco Inter-Switch Link (ISL) header.
   * @param dhost destination address (should be 01:00:0c:00:00)
   * @param type type of frame
   * @param user user defined data
   * @param shost source mac address
   * @param len total length of the encapsulated packet less 18 bytes
   * @param snap SNAP information (0xaaaa03 + vendor code)
   * @param vid 15 bit VLAN ID, 1 bit BPDU or CDP indicator
   * @param portindex port index
   * @param reserved used for FDDI and token ring
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_isl(uint8_t *dhost, uint8_t type, uint8_t user,
  uint8_t *shost, uint16_t len, const uint8_t *snap, uint16_t vid,
  uint16_t portindex, uint16_t reserved, const uint8_t* payload,
  uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an Internet Protocol Security Encapsulating Security Payload header.
   * @param spi security parameter index
   * @param seq ESP sequence number
   * @param iv initialization vector
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ipsec_esp_hdr(uint32_t spi, uint32_t seq, uint32_t iv,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an Internet Protocol Security Encapsulating Security Payload footer.
   * @param len padding length
   * @param nh next header
   * @param auth authentication data
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ipsec_esp_ftr(uint8_t len, uint8_t nh, int8_t *auth,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an Internet Protocol Security Authentication header.
   * @param nh next header
   * @param len payload length
   * @param res reserved
   * @param spi security parameter index
   * @param seq sequence number
   * @param auth authentication data
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ipsec_ah(uint8_t nh, uint8_t len, uint16_t res,
  uint32_t spi, uint32_t seq, uint32_t auth, const uint8_t* payload,
  uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an RFC 1035 version 4 DNS header. Additional DNS payload information
   * should be specified using the payload interface.
   * @param h_len
   * @param id DNS packet id
   * @param flags control flags
   * @param num_q number of questions
   * @param num_anws_rr number of answer resource records
   * @param num_auth_rr number of authority resource records
   * @param num_addi_rr number of additional resource records
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_dnsv4(uint16_t h_len, uint16_t id, uint16_t flags,
  uint16_t num_q, uint16_t num_anws_rr, uint16_t num_auth_rr,
  uint16_t num_addi_rr, const uint8_t* payload, uint32_t payload_s, libnet_t *l,
  libnet_ptag_t ptag);
  
  /**
   * Builds a Routing Information Protocol header (RFCs 1058 and 2453).
   * @param cmd command
   * @param version protocol version
   * @param rd version one: 0, version two: routing domain
   * @param af address family
   * @param rt version one: 0, version two: route tag
   * @param addr IPv4 address
   * @param mask version one: 0, version two: subnet mask
   * @param next_hop version one: 0, version two: next hop address
   * @param metric routing metric
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_rip(uint8_t cmd, uint8_t version, uint16_t rd, uint16_t af,
  uint16_t rt, uint32_t addr, uint32_t mask, uint32_t next_hop,
  uint32_t metric, const uint8_t* payload, uint32_t payload_s, libnet_t *l,
  libnet_ptag_t ptag);
  
  /**
   * Builds an Remote Procedure Call (Version 2) Call message header as
   * specified in RFC 1831. This builder provides the option for
   * specifying the record marking which is required when used with
   * streaming protocols (TCP).
   * @param rm record marking indicating the position in a stream, 0 otherwise
   * @param xid transaction identifier used to link calls and replies
   * @param prog_num remote program specification typically between 0 - 1fffffff
   * @param prog_vers remote program version specification
   * @param procedure procedure to be performed by remote program
   * @param cflavor authentication credential type
   * @param clength credential length (should be 0)
   * @param cdata opaque credential data (currently unused)
   * @param vflavor authentication verifier type
   * @param vlength verifier length (should be 0)
   * @param vdata opaque verifier data (currently unused)
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_rpc_call(uint32_t rm, uint32_t xid, uint32_t prog_num,
  uint32_t prog_vers, uint32_t procedure, uint32_t cflavor, uint32_t clength,
  uint8_t *cdata, uint32_t vflavor, uint32_t vlength, const uint8_t *vdata,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IEEE 802.1d Spanning Tree Protocol (STP) configuration header.
   * STP frames are usually encapsulated inside of an 802.2 + 802.3 frame 
   * combination.
   * @param id protocol id
   * @param version protocol version
   * @param bpdu_type bridge protocol data unit type
   * @param flags flags
   * @param root_id root id
   * @param root_pc root path cost
   * @param bridge_id bridge id
   * @param port_id port id
   * @param message_age message age
   * @param max_age max age
   * @param hello_time hello time
   * @param f_delay forward delay
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_stp_conf(uint16_t id, uint8_t version, uint8_t bpdu_type,
  uint8_t flags, const uint8_t *root_id, uint32_t root_pc, const uint8_t *bridge_id,
  uint16_t port_id, uint16_t message_age, uint16_t max_age, 
  uint16_t hello_time, uint16_t f_delay, const uint8_t* payload,
  uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an IEEE 802.1d Spanning Tree Protocol (STP) topology change
   * notification header. STP frames are usually encapsulated inside of an
   * 802.2 + 802.3 frame combination.
   * @param id protocol id
   * @param version protocol version
   * @param bpdu_type bridge protocol data unit type
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_stp_tcn(uint16_t id, uint8_t version, uint8_t bpdu_type,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds a token ring header.
   * @param ac access control
   * @param fc frame control
   * @param dst destination address
   * @param src source address
   * @param dsap destination service access point
   * @param ssap source service access point
   * @param cf control field
   * @param oui Organizationally Unique Identifier
   * @param type upper layer protocol type
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_token_ring(uint8_t ac, uint8_t fc, const uint8_t *dst, const uint8_t *src,
  uint8_t dsap, uint8_t ssap, uint8_t cf, const uint8_t *oui, uint16_t type,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Auto-builds a token ring header.
   * @param ac access control
   * @param fc frame control
   * @param dst destination address
   * @param dsap destination service access point
   * @param ssap source service access point
   * @param cf control field
   * @param oui Organizationally Unique Identifier
   * @param type upper layer protocol type
   * @param l pointer to a libnet context
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_autobuild_token_ring(uint8_t ac, uint8_t fc, const uint8_t *dst, 
  uint8_t dsap, uint8_t ssap, uint8_t cf, const uint8_t *oui, uint16_t type,
  libnet_t *l);
  
  /**
   * Builds an RFC 2338 Virtual Router Redundacy Protool (VRRP) header. Use the
   * payload interface to specify address and authentication information. To
   * build a "legal" packet, the destination IPv4 address should be the multicast  * address 224.0.0.18, the IP TTL should be set to 255, and the IP protocol
   * should be set to 112.
   * @param version VRRP version (should be 2)
   * @param type VRRP packet type (should be 1 -- ADVERTISEMENT)
   * @param vrouter_id virtual router identification
   * @param priority priority (higher numbers indicate higher priority)
   * @param ip_count number of IPv4 addresses contained in this advertisement
   * @param auth_type type of authentication (0, 1, 2 -- see RFC)
   * @param advert_int interval between advertisements
   * @param sum checksum (0 for libnet to autofill)
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_vrrp(uint8_t version, uint8_t type, uint8_t vrouter_id,
  uint8_t priority, uint8_t ip_count, uint8_t auth_type, uint8_t advert_int,
  uint16_t sum, const uint8_t* payload, uint32_t payload_s, libnet_t *l,
  libnet_ptag_t ptag);
  
  /**
   * Builds an RFC 3032 Multi-Protocol Label Switching (MPLS) header.
   * @param label 20-bit label value
   * @param experimental 3-bit reserved field
   * @param bos 1-bit bottom of stack identifier
   * @param ttl time to live
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_mpls(uint32_t label, uint8_t experimental, uint8_t bos,
  uint8_t ttl, const uint8_t* payload, uint32_t payload_s, libnet_t *l,
  libnet_ptag_t ptag);
  
  /**
   * Builds an RFC 958 Network Time Protocol (NTP) header.
   * @param leap_indicator the leap indicator
   * @param version NTP protocol version
   * @param mode NTP mode
   * @param stratum stratum
   * @param poll polling interval
   * @param precision precision
   * @param delay_int delay interval
   * @param delay_frac delay fraction
   * @param dispersion_int dispersion interval
   * @param dispersion_frac dispersion fraction
   * @param reference_id reference id
   * @param ref_ts_int reference timestamp integer
   * @param ref_ts_frac reference timestamp fraction
   * @param orig_ts_int original timestamp integer
   * @param orig_ts_frac original timestamp fraction
   * @param rec_ts_int receiver timestamp integer
   * @param rec_ts_frac receiver timestamp fraction
   * @param xmt_ts_int transmit timestamp integer
   * @param xmt_ts_frac transmit timestamp integer
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ntp(uint8_t leap_indicator, uint8_t version, uint8_t mode,
  uint8_t stratum, uint8_t poll, uint8_t precision, uint16_t delay_int,
  uint16_t delay_frac, uint16_t dispersion_int, uint16_t dispersion_frac,
  uint32_t reference_id, uint32_t ref_ts_int, uint32_t ref_ts_frac,
  uint32_t orig_ts_int, uint32_t orig_ts_frac, uint32_t rec_ts_int,
  uint32_t rec_ts_frac, uint32_t xmt_ts_int, uint32_t xmt_ts_frac,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * @param len
   * @param type
   * @param rtr_id
   * @param area_id
   * @param sum
   * @param autype
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ospfv2(uint16_t len, uint8_t type, uint32_t rtr_id,
  uint32_t area_id, uint16_t sum, uint16_t autype, const uint8_t* payload,
  uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * @param netmask
   * @param interval
   * @param opts
   * @param priority
   * @param dead_int
   * @param des_rtr
   * @param bkup_rtr
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ospfv2_hello(uint32_t netmask, uint16_t interval, uint8_t opts,
  uint8_t priority, uint32_t dead_int, uint32_t des_rtr, uint32_t bkup_rtr,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * @param netmask
   * @param interval
   * @param opts
   * @param priority
   * @param dead_int
   * @param des_rtr
   * @param bkup_rtr
   * @param neighbor
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  libnet_ptag_t
  libnet_build_ospfv2_hello_neighbor(uint32_t netmask, uint16_t interval, uint8_t opts,
  uint8_t priority, uint32_t dead_int, uint32_t des_rtr, uint32_t bkup_rtr, uint32_t neighbor,
  const uint8_t *payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * @param dgram_len
   * @param opts
   * @param type
   * @param seqnum
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ospfv2_dbd(uint16_t dgram_len, uint8_t opts, uint8_t type,
  uint32_t seqnum, const uint8_t* payload, uint32_t payload_s, libnet_t *l,
  libnet_ptag_t ptag);
   
  /**
   * @param type
   * @param lsid
   * @param advrtr
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ospfv2_lsr(uint32_t type, uint32_t lsid, uint32_t advrtr,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
   
  /**
   * @param num
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ospfv2_lsu(uint32_t num, const uint8_t* payload, uint32_t payload_s,
  libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * @param age
   * @param opts
   * @param type
   * @param lsid
   * @param advrtr
   * @param seqnum
   * @param sum
   * @param len
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ospfv2_lsa(uint16_t age, uint8_t opts, uint8_t type,
  uint32_t lsid, uint32_t advrtr, uint32_t seqnum, uint16_t sum, uint16_t len,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
   
  /**
   * @param flags
   * @param num
   * @param id
   * @param data
   * @param type
   * @param tos
   * @param metric
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ospfv2_lsa_rtr(uint16_t flags, uint16_t num, uint32_t id,
  uint32_t data, uint8_t type, uint8_t tos, uint16_t metric, const uint8_t* payload,
  uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
   
  /**
   * @param nmask
   * @param rtrid
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ospfv2_lsa_net(uint32_t nmask, uint32_t rtrid, const uint8_t* payload,
  uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
   
  /**
   * @param nmask
   * @param metric
   * @param tos
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ospfv2_lsa_sum(uint32_t nmask, uint32_t metric, uint32_t tos,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
   
  /**
   * @param nmask
   * @param metric
   * @param fwdaddr
   * @param tag
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_ospfv2_lsa_as(uint32_t nmask, uint32_t metric, uint32_t fwdaddr,
  uint32_t tag, const uint8_t* payload, uint32_t payload_s, libnet_t *l,
  libnet_ptag_t ptag);
  
  /**
   * Builds a generic libnet protocol header. This is useful for including an
   * optional payload to a packet that might need to change repeatedly inside
   * of a loop. This won't work for TCP or IP payload, they have special types
   * (this is probably a bug).
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_data(const uint8_t* payload, uint32_t payload_s, libnet_t *l,
  libnet_ptag_t ptag);
  
  /**
   * @param opcode
   * @param htype
   * @param hlen
   * @param hopcount
   * @param xid
   * @param secs
   * @param flags
   * @param cip
   * @param yip
   * @param sip
   * @param gip
   * @param chaddr client hardware address, length is hlen
   * @param sname server host name, a null terminated string
   * @param file boot file name, a null terminated string
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_dhcpv4(uint8_t opcode, uint8_t htype, uint8_t hlen,
  uint8_t hopcount, uint32_t xid, uint16_t secs, uint16_t flags,
  uint32_t cip, uint32_t yip,  uint32_t sip, uint32_t gip, const uint8_t *chaddr,
  const char *sname, const char *file, const uint8_t* payload, uint32_t payload_s, 
  libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * @param opcode
   * @param htype
   * @param hlen
   * @param hopcount
   * @param xid
   * @param secs
   * @param flags
   * @param cip
   * @param yip
   * @param sip
   * @param gip
   * @param chaddr client hardware address, length is hlen
   * @param sname server host name, a null terminated string
   * @param file boot file name, a null terminated string
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_bootpv4(uint8_t opcode, uint8_t htype, uint8_t hlen,
  uint8_t hopcount, uint32_t xid, uint16_t secs, uint16_t flags,
  uint32_t cip, uint32_t yip,  uint32_t sip, uint32_t gip, const uint8_t *chaddr,
  const char *sname, const char *file, const uint8_t* payload, uint32_t payload_s, 
  libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * @param fv see libnet_build_gre().
   * @return size
   * @see libnet_build_gre().
   */
  LIBNET_API
  uint32_t
  libnet_getgre_length(uint16_t fv);
  
  /**
   * Generic Routing Encapsulation (GRE - RFC 1701) is used to encapsulate any
   * protocol. Hence, the IP part of the packet is usually referred as "delivery
   * header". It is then followed by the GRE header and finally the encapsulated
   * packet (IP or whatever).
   * As GRE is very modular, the first GRE header describes the structure of the
   * header, using bits and flag to specify which fields will be present in the
   * header.
   * @param fv the 16 0 to 7: which fields are included in the header (checksum,
   *   seq. number, key, ...), bits 8 to 12: flag, bits 13 to 15: version.
   * @param type which protocol is encapsulated (PPP, IP, ...)
   * @param sum checksum (0 for libnet to auto-fill).
   * @param offset byte offset from the start of the routing field to the first byte of the SRE
   * @param key inserted by the encapsulator to authenticate the source
   * @param seq sequence number used by the receiver to sort the packets
   * @param len size of the GRE packet
   * @param payload
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_gre(uint16_t fv, uint16_t type, uint16_t sum,
  uint16_t offset, uint32_t key, uint32_t seq, uint16_t len,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Generic Routing Encapsulation (GRE - RFC 1701) is used to encapsulate any
   * protocol. Hence, the IP part of the packet is usually referred as "delivery
   * header". It is then followed by the GRE header and finally the encapsulated
   * packet (IP or whatever).
   * As GRE is very modular, the first GRE header describes the structure of the
   * header, using bits and flag to specify which fields will be present in the
   * header.
   * @param fv the 16 0 to 7: which fields are included in the header (checksum, seq. number, key, ...), bits 8 to 12: flag, bits 13 to 15: version.
   * @param type which protocol is encapsulated (PPP, IP, ...)
   * @param sum checksum (0 for libnet to auto-fill).
   * @param offset byte offset from the start of the routing field to the first byte of the SRE
   * @param key inserted by the encapsulator to authenticate the source
   * @param seq sequence number used by the receiver to sort the packets
   * @param len size of the GRE packet
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_egre(uint16_t fv, uint16_t type, uint16_t sum,
  uint16_t offset, uint32_t key, uint32_t seq, uint16_t len,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * @param af
   * @param offset
   * @param length
   * @param routing
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_gre_sre(uint16_t af, uint8_t offset, uint8_t length,
  uint8_t *routing, const uint8_t* payload, uint32_t payload_s, libnet_t *l,
  libnet_ptag_t ptag);
  
  /**
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_gre_last_sre(libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an RFC 1771 Border Gateway Protocol 4 (BGP-4) header. The primary
   * function of a BGP speaking system is to exchange network reachability
   * information with other BGP systems. This network reachability information
   * includes information on the list of  Autonomous Systems (ASs) that
   * reachability information traverses.  This information is sufficient to
   * construct a graph of AS connectivity from which routing loops may be pruned
   * and some policy decisions at the AS level may be enforced.
   * This function builds the base BGP header which is used as a preamble before
   * any other BGP header. For example, a BGP KEEPALIVE message may be built with
   * only this function, while an error notification requires a subsequent call
   * to libnet_build_bgp4_notification.
   * @param marker a value the receiver can predict (if the message type is not BGP OPEN, or no authentication is used, these 16 bytes are normally set as all ones)
   * @param len total length of the BGP message, including the header
   * @param type type code of the message (OPEN, UPDATE, NOTIFICATION or KEEPALIVE)
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_bgp4_header(uint8_t marker[LIBNET_BGP4_MARKER_SIZE],
  uint16_t len, uint8_t type, const uint8_t* payload, uint32_t payload_s,
  libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an RFC 1771 Border Gateway Protocol 4 (BGP-4) OPEN header. This is
   * the first message sent by each side of a BGP connection. The optional
   * parameters options should be constructed using the payload interface (see
   * RFC 1771 for the options structures).
   * @param version protocol version (should be set to 4)
   * @param src_as Autonomous System of the sender
   * @param hold_time used to compute the maximum allowed time between the receipt of KEEPALIVE, and/or UPDATE messages by the sender
   * @param bgp_id BGP identifier of the sender
   * @param opt_len total length of the  optional parameters field in bytes
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_bgp4_open(uint8_t version, uint16_t src_as, uint16_t hold_time,
  uint32_t bgp_id, uint8_t opt_len, const uint8_t* payload, uint32_t payload_s,
  libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an RFC 1771 Border Gateway Protocol 4 (BGP-4) update header. Update
   * messages are used to transfer routing information between BGP peers.
   * @param unfeasible_rt_len indicates the length of the (next) "withdrawn routes" field in bytes
   * @param withdrawn_rt list of IP addresses prefixes for the routes that are being withdrawn; each IP address prefix is built as a 2-tuple <length (1 byte), prefix (variable)>
   * @param total_path_attr_len indicates the length of the (next) "path attributes" field in bytes
   * @param path_attributes each attribute is a 3-tuple <type (2 bytes), length, value>
   * @param info_len indicates the length of the (next) "network layer reachability information" field in bytes (needed for internal memory size calculation)
   * @param reachability_info 2-tuples <length (1 byte), prefix (variable)>.
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_bgp4_update(uint16_t unfeasible_rt_len, const uint8_t *withdrawn_rt,
  uint16_t total_path_attr_len, const uint8_t *path_attributes, uint16_t info_len,
  uint8_t *reachability_info, const uint8_t* payload, uint32_t payload_s,
  libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds an RFC 1771 Border Gateway Protocol 4 (BGP-4) notification header.
   * A NOTIFICATION message is sent when an error condition is detected. Specific
   * error information may be passed through the payload interface.
   * @param err_code type of notification
   * @param err_subcode more specific information about the reported error.
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_bgp4_notification(uint8_t err_code, uint8_t err_subcode,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds a Sebek header. The Sebek protocol was designed by the Honeynet
   * Project as a transport mechanism for post-intrusion forensic data. More
   * information may be found here: http://www.honeynet.org/papers/sebek.pdf.
   * @param magic identify packets that should be hidden 
   * @param version protocol version, currently 1 
   * @param type type of record (read data is type 0, write data is type 1) 
   * @param counter PDU counter used to identify when packet are lost 
   * @param time_sec seconds since EPOCH according to the honeypot 
   * @param time_usec residual microseconds 
   * @param pid PID 
   * @param uid UID 
   * @param fd FD 
   * @param cmd 12 first characters of the command 
   * @param length length in bytes of the PDU's body 
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_sebek(uint32_t magic, uint16_t version, uint16_t type, 
  uint32_t counter, uint32_t time_sec, uint32_t time_usec, uint32_t pid,
  uint32_t uid, uint32_t fd, uint8_t cmd[SEBEK_CMD_LENGTH], uint32_t length, 
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds a HSRP header. HSRP is a Cisco proprietary protocol defined in
   * RFC 2281
   * @param version version of the HSRP messages
   * @param opcode type of message
   * @param state current state of the router
   * @param hello_time period in seconds between hello messages
   * @param hold_time seconds that the current hello message is valid
   * @param priority priority for the election process
   * @param group standby group
   * @param reserved reserved field
   * @param authdata password
   * @param virtual_ip virtual ip address
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_hsrp(uint8_t version, uint8_t opcode, uint8_t state, 
  uint8_t hello_time, uint8_t hold_time, uint8_t priority, uint8_t group,
  uint8_t reserved, uint8_t authdata[HSRP_AUTHDATA_LENGTH], uint32_t virtual_ip,
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Builds a link layer header for an initialized l. The function
   * determines the proper link layer header format from how l was initialized.
   * The function current supports Ethernet and Token Ring link layers.
   * @param dst the destination MAC address
   * @param src the source MAC address
   * @param oui Organizationally Unique Identifier (unused for Ethernet)
   * @param type the upper layer protocol type
   * @param payload optional payload or NULL
   * @param payload_s payload length or 0
   * @param l pointer to a libnet context
   * @param ptag protocol tag to modify an existing header, 0 to build a new one
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_build_link(const uint8_t *dst, const uint8_t *src, const uint8_t *oui, uint16_t type, 
  const uint8_t* payload, uint32_t payload_s, libnet_t *l, libnet_ptag_t ptag);
  
  /**
   * Automatically builds a link layer header for an initialized l. The function
   * determines the proper link layer header format from how l was initialized.
   * The function current supports Ethernet and Token Ring link layers.
   * @param dst the destination MAC address
   * @param oui Organizationally Unique Identifier (unused for Ethernet)
   * @param type the upper layer protocol type
   * @param l pointer to a libnet context
   * @return protocol tag value on success
   * @retval -1 on error
   */
  LIBNET_API
  libnet_ptag_t
  libnet_autobuild_link(const uint8_t *dst, const uint8_t *oui, uint16_t type,
  libnet_t *l);
  
  /**
   * Writes a prebuilt packet to the network. The function assumes that l was
   * previously initialized (via a call to libnet_init()) and that a 
   * previously constructed packet has been built inside this context (via one or
   * more calls to the libnet_build* family of functions) and is ready to go.
   * Depending on how libnet was initialized, the function will write the packet
   * to the wire either via the raw or link layer interface. The function will
   * also bump up the internal libnet stat counters which are retrievable via
   * libnet_stats().
   * @param l pointer to a libnet context
   * @return the number of bytes written
   * @retval -1 on error
   */
  LIBNET_API
  int
  libnet_write(libnet_t *l);
  
  /**
   * Returns the IP address for the device libnet was initialized with. If
   * libnet was initialized without a device (in raw socket mode) the function
   * will attempt to find one. If the function fails and returns -1 a call to 
   * libnet_geterrror() will tell you why.
   * @param l pointer to a libnet context
   * @return a big endian IP address suitable for use in a libnet_build function
   * @retval -1
   */
  LIBNET_API
  uint32_t
  libnet_get_ipaddr4(libnet_t *l);
  
  /**
   * Returns the IPv6 address for the device libnet was initialized with. If
   * libnet was initialized without a device (in raw socket mode) the function
   * will attempt to find one. If the function fails and returns in6addr_error, a
   * call to libnet_geterrror() will tell you why.
   * This function is not yet implemented for Win32 platforms.
   * @param l pointer to a libnet context
   * @retval in6addr_error on failure
   */
  LIBNET_API
  struct libnet_in6_addr
  libnet_get_ipaddr6(libnet_t *l);
  
  /**
   * Returns the MAC address for the device libnet was initialized with. If
   * libnet was initialized without a device the function will attempt to find
   * one. If the function fails and returns NULL a call to libnet_geterror() will
   * tell you why.
   * @param l pointer to a libnet context
   * @return a pointer to the MAC address or NULL
   */
  LIBNET_API
  struct libnet_ether_addr *
  libnet_get_hwaddr(libnet_t *l);
  
  /**
   * Takes a colon separated hexidecimal address (from the command line) and
   * returns a bytestring suitable for use in a libnet_build function. Note this
   * function performs an implicit malloc and the return value should be freed
   * after its use.
   * @param s the string to be parsed
   * @param len the resulting size of the returned byte string
   * @return a byte string or NULL on failure
   */
  LIBNET_API
  uint8_t *
  libnet_hex_aton(const char *s, int *len);
  
  /**
   * Returns the version of libnet.
   * @return the libnet version
   */
  LIBNET_API
  const char *
  libnet_version(void);
  
  /**
   * [Advanced Interface]
   * Yanks a prebuilt, wire-ready packet from the given libnet context. If
   * libnet was configured to do so (which it is by default) the packet will have
   * all checksums written in. This function is part of the advanced interface
   * and is only available when libnet is initialized in advanced mode. It is
   * important to note that the function performs an implicit malloc() and a
   * corresponding call to libnet_adv_free_packet() should be made to free the
   * memory packet occupies. If the function fails libnet_geterror() can tell you
   * why.
   * @param l pointer to a libnet context
   * @param packet will contain the wire-ready packet
   * @param packet_s will contain the packet size
   * @retval 1 on success
   * @retval -1 on failure  
   */
  LIBNET_API
  int
  libnet_adv_cull_packet(libnet_t *l, uint8_t **packet, uint32_t *packet_s);
  
  /**
   * [Advanced Interface] 
   * Pulls the header from the specified ptag from the given libnet context. This
   * function is part of the advanced interface and is only available when libnet
   * is initialized in advanced mode. If the function fails libnet_geterror() can
   * tell you why.
   * @param l pointer to a libnet context
   * @param ptag the ptag referencing the header to pull
   * @param header will contain the header
   * @param header_s will contain the header size
   * @retval 1 on success
   * @retval -1 on failure  
   */
  LIBNET_API
  int
  libnet_adv_cull_header(libnet_t *l, libnet_ptag_t ptag, uint8_t **header,
  uint32_t *header_s);
  
  /**
   * [Advanced Interface] 
   * Writes a packet the network at the link layer. This function is useful to
   * write a packet that has been constructed by hand by the application
   * programmer or, more commonly, to write a packet that has been returned by
   * a call to libnet_adv_cull_packet(). This function is part of the advanced
   * interface and is only available when libnet is initialized in advanced mode.
   * If the function fails libnet_geterror() can tell you why.
   * @param l pointer to a libnet context
   * @param packet a pointer to the packet to inject
   * @param packet_s the size of the packet
   * @return the number of bytes written
   * @retval -1 on failure
   */
  LIBNET_API
  int
  libnet_adv_write_link(libnet_t *l, const uint8_t *packet, uint32_t packet_s);
  
  /**
   * [Advanced Interface] 
   * Writes a packet the network at the raw socket layer. This function is useful
   * to write a packet that has been constructed by hand by the application
   * programmer or, more commonly, to write a packet that has been returned by
   * a call to libnet_adv_cull_packet(). This function is part of the advanced
   * interface and is only available when libnet is initialized in advanced mode.
   * If the function fails libnet_geterror() can tell you why.
   * @param l pointer to a libnet context
   * @param packet a pointer to the packet to inject
   * @param packet_s the size of the packet
   * @return the number of bytes written
   * @retval -1 on failure
   */
  LIBNET_API
  int
  libnet_adv_write_raw_ipv4(libnet_t *l, const uint8_t *packet, uint32_t packet_s);
  
  /**
   * [Advanced Interface] 
   * Frees the memory allocated when libnet_adv_cull_packet() is called.
   * @param l pointer to a libnet context
   * @param packet a pointer to the packet to free
   */
  LIBNET_API
  void
  libnet_adv_free_packet(libnet_t *l, uint8_t *packet);
  
  /**
   * [Context Queue] 
   * Adds a new context to the libnet context queue. If no queue exists, this
   * function will create the queue and add the specified libnet context as the
   * first entry on the list. The functions checks to ensure niether l nor label
   * are NULL, and that label doesn't refer to an existing context already in the
   * queue. Additionally, l should refer to a libnet context previously
   * initialized with a call to libnet_init(). If the context queue in write
   * locked, this function will fail.
   * @param l pointer to a libnet context
   * @param label a canonical name given to recognize the new context, no longer than LIBNET_LABEL_SIZE
   * @retval 1 on success
   * @retval -1 on failure
  */
  int 
  libnet_cq_add(libnet_t *l, char *label);
  
  /**
   * [Context Queue] 
   * Removes a specified context from the libnet context queue by specifying the
   * libnet context pointer. Note the function will remove the specified context
   * from the context queue and cleanup internal memory from the queue, it is up
   * to the application programmer to free the returned libnet context with a
   * call to libnet_destroy(). Also, as it is not necessary to keep the libnet
   * context pointer when initially adding it to the context queue, most
   * application programmers will prefer to refer to entries on the context
   * queue by canonical name and would use libnet_cq_remove_by_label(). If the
   * context queue is write locked, this function will fail.
   * @param l pointer to a libnet context
   * @return the pointer to the removed libnet context
   * @retval NULL on failure
   */
  LIBNET_API
  libnet_t *
  libnet_cq_remove(libnet_t *l);
  
  /** 
   * [Context Queue] 
   * Removes a specified context from the libnet context queue by specifying the
   * canonical name. Note the function will remove the specified context from
   * the context queue and cleanup internal memory from the queue, it is up to 
   * the application programmer to free the returned libnet context with a call
   * to libnet_destroy(). If the context queue is write locked, this function
   * will fail.
   * @param label canonical name of the context to remove
   * @return the pointer to the removed libnet context
   * @retval NULL on failure
   */
  LIBNET_API   
  libnet_t *
  libnet_cq_remove_by_label(char *label);
   
  /**
   * [Context Queue] 
   * Returns the canonical label associated with the context.
   * @param l pointer to a libnet context
   * @return pointer to the libnet context's label
   */
  LIBNET_API   
  const char *
  libnet_cq_getlabel(libnet_t *l);
   
  /**
   * [Context Queue] 
   * Locates a libnet context from the queue, indexed by a canonical label.
   * @param label canonical label of the libnet context to retrieve
   * @return the expected libnet context
   * @retval NULL on failure
   */
  LIBNET_API
  libnet_t *
  libnet_cq_find_by_label(char *label);
    
  /**
   * [Context Queue] 
   * Destroys the entire context queue, calling libnet_destroy() on each
   * member context.
   */
  LIBNET_API
  void
  libnet_cq_destroy(void);
  
  /**
   * [Context Queue] 
   * Intiailizes the interator interface and set a write lock on the entire
   * queue. This function is intended to be called just prior to interating
   * through the entire list of contexts (with the probable intent of inject a
   * series of packets in rapid succession). This function is often used as
   * per the following:
   *
   *    for (l = libnet_cq_head(); libnet_cq_last(); l = libnet_cq_next())
   *    {
   *         ...
   *    }
   *
   * Much of the time, the application programmer will use the iterator as it is
   * written above; as such, libnet provides a macro to do exactly that,
   * for_each_context_in_cq(l). Warning: do not call the iterator more than once
   * in a single loop.
   * @return the head of the context queue
   */
  LIBNET_API
  libnet_t *
  libnet_cq_head(void);
  
  /**
   * [Context Queue] 
   * Check whether the iterator is at the last context in the queue.
   * @retval 1 if at the end of the context queue
   * @retval 0 otherwise
   */
  LIBNET_API
  int
  libnet_cq_last(void);
  
  /**
   * [Context Queue] 
   * Get next context from the context queue.
   * @return the next context from the context queue
   */
  LIBNET_API
  libnet_t *
  libnet_cq_next(void);
  
  /**
   * [Context Queue] 
   * Function returns the number of libnet contexts that are in the queue.
   * @return the number of libnet contexts currently in the queue
   */
  LIBNET_API
  uint32_t
  libnet_cq_size(void);
  
  /**
   * [Context Queue]
   */
  LIBNET_API
  uint32_t
  libnet_cq_end_loop(void);
  
  /**
   * [Diagnostic] 
   * Prints the contents of the given context.
   * @param l pointer to a libnet context
   */
  LIBNET_API
  void
  libnet_diag_dump_context(libnet_t *l);
  
  /**
   * [Diagnostic] 
   * Prints the contents of every pblock.
   * @param l pointer to a libnet context
   */
  LIBNET_API
  void
  libnet_diag_dump_pblock(libnet_t *l);
  
  /**
   * [Diagnostic] 
   * Returns the canonical name of the pblock type.
   * @param type pblock type
   * @return a string representing the pblock type type
   * @retval "unknown" for an unknown value
   */
  LIBNET_API
  char *
  libnet_diag_dump_pblock_type(uint8_t type);
  
  /**
   * [Diagnostic] 
   * Function prints the contents of the supplied buffer to the supplied
   * stream pointer. Will swap endianness based disposition of mode variable.
   * Useful to be used in conjunction with the advanced interface and a culled
   * packet.
   * @param packet the packet to print
   * @param len length of the packet in bytes
   * @param swap 1 to swap byte order, 0 to not.
   *   Counter-intuitively, it is necessary to swap in order to see the byte
   *   order as it is on the wire (this may be a bug).
   * @param stream a stream pointer to print to
   */
  void
  libnet_diag_dump_hex(const uint8_t *packet, uint32_t len, int swap, FILE *stream);
  
  /*
   * [Internal] 
   */
  LIBNET_API
  int
  libnet_write_raw_ipv4(libnet_t *l, const uint8_t *packet, uint32_t size);
  
  /*
   * [Internal] 
   */
  LIBNET_API
  int
  libnet_write_raw_ipv6(libnet_t *l, const uint8_t *packet, uint32_t size);
  
  /*
   * [Internal] 
   */
  LIBNET_API
  int
  libnet_write_link(libnet_t *l, const uint8_t *packet, uint32_t size);
  
  /*
   * [Internal] 
   */
  int
  libnet_open_raw4(libnet_t *l);
  
  /*
   * [Internal] 
   */
  LIBNET_API
  int
  libnet_close_raw4(libnet_t *l);
  
  /*
   * [Internal] 
   */
  int
  libnet_open_raw6(libnet_t *l);
         
  /*
   * [Internal] 
   */
  int
  libnet_close_raw6(libnet_t *l);
  
  /*
   * [Internal] 
   */
  int
  libnet_select_device(libnet_t *l);
  
  /*
   * [Internal] 
   */
  int
  libnet_open_link(libnet_t *l);
  
  /*
   * [Internal] 
   */
  int
  libnet_close_link(libnet_t *l);
  
  /*
   * [Internal]
   *   THIS FUNCTION IS BROKEN. IT WILL SEGFAULT OR CORRUPT MEMORY, OR JUST SILENTLY DO THE
   *   WRONG THING IF NOT CALLED CORRECTLY, AND CALLING IT CORRECTLY IS UNDOCUMENTED, AND
   *   ALMOST IMPOSSIBLE. YOU HAVE BEEN WARNED.
   */
  int
  libnet_do_checksum(libnet_t *l, uint8_t *iphdr, int protocol, int h_len);
  
  /* Calculate internet checksums.
   *
   * IP (TCP, UDP, IGMP, ICMP, etc...) checksums usually need information from
   * the IP header to construct the "pseudo header", this function takes a
   * pointer to that header, the buffer boundaries, the "h_len" (see pblock_t for
   * a description, it is increasingly unused, though, and I'm trying to remove it
   * altogether), and the protocol number for the protocol that is to be
   * checksummed.
   *
   * Finding that protocol requires that the IP header be well-formed... so this
   * won't work well for invalid packets. But then, what is the valid checksum
   * for a invalid packet, anyhow?
   *
   * This doesn't work well for non-inet checksums, sorry, that's an original design
   * flaw. pblock_t needs a pointer in it, to a packet assembly function that can be
   * called at runtime to do assembly and checksumming.
   */
  LIBNET_API
  int
  libnet_inet_checksum(libnet_t *l, uint8_t *iphdr, int protocol, int h_len, const uint8_t *beg, const uint8_t * end);
  
  /*
   * [Internal] 
   */
  LIBNET_API
  uint32_t
  libnet_compute_crc(uint8_t *buf, uint32_t len);
  
  /*
   * [Internal] 
   */
  LIBNET_API
  uint16_t
  libnet_ip_check(uint16_t *addr, int len);
  
  /*
   * [Internal] 
   */
  LIBNET_API
  int
  libnet_in_cksum(uint16_t *addr, int len);
  
  /*
   * [Internal] 
   * If ptag is 0, function will create a pblock for the protocol unit type,
   * append it to the list and return a pointer to it.  If ptag is not 0,
   * function will search the pblock list for the specified protocol block 
   * and return a pointer to it.
   */
  LIBNET_API
  libnet_pblock_t *
  libnet_pblock_probe(libnet_t *l, libnet_ptag_t ptag, uint32_t b_len, 
  uint8_t type);
  
  /*
   * [Internal] 
   * Function creates the pblock list if l->protocol_blocks == NULL or appends
   * an entry to the doubly linked list.
   */
  LIBNET_API
  libnet_pblock_t *
  libnet_pblock_new(libnet_t *l, uint32_t b_len);
  
  /*
   * [Internal] 
   * Function swaps two pblocks in memory.
   */
  LIBNET_API
  int
  libnet_pblock_swap(libnet_t *l, libnet_ptag_t ptag1, libnet_ptag_t ptag2);
  
  /*
   * [Internal] 
   * Function inserts ptag2 before ptag1 in the doubly linked list.
   */
  LIBNET_API
  int
  libnet_pblock_insert_before(libnet_t *l, libnet_ptag_t ptag1,
  libnet_ptag_t ptag2);
  
  /*
   * [Internal] 
   * Function removes a pblock from context 
   */
  LIBNET_API
  void
  libnet_pblock_delete(libnet_t *l, libnet_pblock_t *p);
  
  /*
   * [Internal] 
   * Function updates the pblock meta-information.  Internally it updates the
   * ptag with a monotonically increasing variable kept in l.  This way each
   * pblock has a successively increasing ptag identifier.
   */
  LIBNET_API
  libnet_ptag_t
  libnet_pblock_update(libnet_t *l, libnet_pblock_t *p, uint32_t h, uint8_t type);
  
  
  /*
   * [Internal] 
   * Function locates a given block by it's ptag. 
   */
  LIBNET_API
  libnet_pblock_t *
  libnet_pblock_find(libnet_t *l, libnet_ptag_t ptag);
  
  /*
   * [Internal] 
   * Function copies protocol block data over.
   */
  LIBNET_API
  int
  libnet_pblock_append(libnet_t *l, libnet_pblock_t *p, const void *buf, uint32_t len);
  
  /*
   * [Internal] 
   * Function sets pblock flags.
   */
  LIBNET_API
  void
  libnet_pblock_setflags(libnet_pblock_t *p, uint8_t flags);
  
  /*
   * [Internal] 
   * Function returns the protocol number for the protocol block type.  If
   * the type is unknown, the function defaults to returning IPPROTO_IP.
   */
  LIBNET_API
  int
  libnet_pblock_p2p(uint8_t type);
  
  /*
   * [Internal] 
   * Function assembles the protocol blocks into a packet, checksums are
   * calculated if that was requested.
   */
  LIBNET_API
  int
  libnet_pblock_coalesce(libnet_t *l, uint8_t **packet, uint32_t *size);
  
  #if !(__WIN32__)
  /*
   * [Internal] 
   * By testing if we can retrieve the FLAGS of an interface
   * we can know if it exists or not and if it is up.
   */
  int
  libnet_check_iface(libnet_t *l);
  #endif
  
  #if defined(__WIN32__)
  /*
   * [Internal] 
   */
  BYTE *
  libnet_win32_get_remote_mac(libnet_t *l, DWORD IP);
  
  /*
   * [Internal] 
   */
  int
  libnet_close_link_interface(libnet_t *l);
  
  /*
   * [Internal] 
   */
  BYTE * 
  libnet_win32_read_arp_table(DWORD IP);
  #endif
  #endif  /* __LIBNET_FUNCTIONS_H */
  
  /**
   * Local Variables:
   *  indent-tabs-mode: nil
   *  c-file-style: "stroustrup"
   * End:
   */
  