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NETINTRO(4)		 BSD Kernel Interfaces Manual		   NETINTRO(4)

     networking	-- introduction	to networking facilities

     #include <sys/types.h>
     #include <sys/time.h>
     #include <sys/socket.h>
     #include <net/if.h>
     #include <net/route.h>

     This section is a general introduction to the networking facilities
     available in the system.  Documentation in	this part of section 4 is bro-
     ken up into three areas: protocol families	(domains), protocols, and
     network interfaces.

     All network protocols are associated with a specific protocol family.  A
     protocol family provides basic services to	the protocol implementation to
     allow it to function within a specific network environment.  These	ser-
     vices may include packet fragmentation and	reassembly, routing, address-
     ing, and basic transport.	A protocol family may support multiple methods
     of	addressing, though the current protocol	implementations	do not.	 A
     protocol family is	normally comprised of a	number of protocols, one per
     socket(2) type.  It is not	required that a	protocol family	support	all
     socket types.  A protocol family may contain multiple protocols support-
     ing the same socket abstraction.

     A protocol	supports one of	the socket abstractions	detailed in socket(2).
     A specific	protocol may be	accessed either	by creating a socket of	the
     appropriate type and protocol family, or by requesting the	protocol ex-
     plicitly when creating a socket.  Protocols normally accept only one type
     of	address	format,	usually	determined by the addressing structure inher-
     ent in the	design of the protocol family/network architecture.  Certain
     semantics of the basic socket abstractions	are protocol specific.	All
     protocols are expected to support the basic model for their particular
     socket type, but may, in addition,	provide	non-standard facilities	or ex-
     tensions to a mechanism.  For example, a protocol supporting the
     SOCK_STREAM abstraction may allow more than one byte of out-of-band data
     to	be transmitted per out-of-band message.

     A network interface is similar to a device	interface.  Network interfaces
     comprise the lowest layer of the networking subsystem, interacting	with
     the actual	transport hardware.  An	interface may support one or more pro-
     tocol families and/or address formats.  The SYNOPSIS section of each net-
     work interface entry gives	a sample specification of the related drivers
     for use in	providing a system description to the config(8)	program.  The
     DIAGNOSTICS section lists messages	which may appear on the	console	and/or
     in	the system error log, /var/log/messages	(see syslogd(8)), due to er-
     rors in device operation.

     The system	currently supports the Internet	protocols, the Xerox Network
     Systems(tm) protocols, and	some of	the ISO	OSI protocols.	Raw socket in-
     terfaces are provided to the IP protocol layer of the Internet, and to
     the IDP protocol of Xerox NS.  Consult the	appropriate manual pages in
     this section for more information regarding the support for each protocol

     Associated	with each protocol family is an	address	format.	 All network
     addresses adhere to a general structure, called a sockaddr, described be-
     low.  However, each protocol imposes finer	and more specific structure,
     generally renaming	the variant, which is discussed	in the protocol	family
     manual page alluded to above.

	   struct sockaddr {
	       u_char	   sa_len;
	       u_char	   sa_family;
	       char	   sa_data[14];

     The field sa_len contains the total length	of the structure, which	may
     exceed 16 bytes.  The following address values for	sa_family are known to
     the system	(and additional	formats	are defined for	possible future	imple-

     #define	AF_UNIX	     1	  /* local to host (pipes, portals) */
     #define	AF_INET	     2	  /* internetwork: UDP,	TCP, etc. */
     #define	AF_NS	     6	  /* Xerox NS protocols	*/
     #define	AF_CCITT     10	  /* CCITT protocols, X.25 etc */
     #define	AF_HYLINK    15	  /* NSC Hyperchannel */
     #define	AF_ISO	     18	  /* ISO protocols */

     FreeBSD provides some packet routing facilities.  The kernel maintains a
     routing information database, which is used in selecting the appropriate
     network interface when transmitting packets.

     A user process (or	possibly multiple co-operating processes) maintains
     this database by sending messages over a special kind of socket.  This
     supplants fixed size ioctl(2) used	in earlier releases.

     This facility is described	in route(4).

     Each network interface in a system	corresponds to a path through which
     messages may be sent and received.	 A network interface usually has a
     hardware device associated	with it, though	certain	interfaces such	as the
     loopback interface, lo(4),	do not.

     The following ioctl(2) calls may be used to manipulate network inter-
     faces.  The ioctl() is made on a socket (typically	of type	SOCK_DGRAM) in
     the desired domain.  Most of the requests supported in earlier releases
     take an ifreq structure as	its parameter.	This structure has the form

     struct  ifreq {
     #define	IFNAMSIZ    16
	 char	 ifr_name[IFNAMSIZ];	    /* if name,	e.g. "en0" */
	 union {
	     struct    sockaddr	ifru_addr;
	     struct    sockaddr	ifru_dstaddr;
	     struct    sockaddr	ifru_broadaddr;
	     short     ifru_flags[2];
	     short     ifru_index;
	     int       ifru_metric;
	     int       ifru_mtu;
	     int       ifru_phys;
	     int       ifru_media;
	     caddr_t   ifru_data;
	     int       ifru_cap[2];
	 } ifr_ifru;
     #define ifr_addr	   ifr_ifru.ifru_addr	   /* address */
     #define ifr_dstaddr   ifr_ifru.ifru_dstaddr   /* other end	of p-to-p link */
     #define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast	address	*/
     #define ifr_flags	   ifr_ifru.ifru_flags[0]  /* flags (low 16 bits) */
     #define ifr_flagshigh ifr_ifru.ifru_flags[1]  /* flags (high 16 bits) */
     #define ifr_metric	   ifr_ifru.ifru_metric	   /* metric */
     #define ifr_mtu	   ifr_ifru.ifru_mtu	   /* mtu */
     #define ifr_phys	   ifr_ifru.ifru_phys	   /* physical wire */
     #define ifr_media	   ifr_ifru.ifru_media	   /* physical media */
     #define ifr_data	   ifr_ifru.ifru_data	   /* for use by interface */
     #define ifr_reqcap	   ifr_ifru.ifru_cap[0]	   /* requested	capabilities */
     #define ifr_curcap	   ifr_ifru.ifru_cap[1]	   /* current capabilities */
     #define ifr_index	   ifr_ifru.ifru_index	   /* interface	index */

     Calls which are now deprecated are:

     SIOCSIFADDR     Set interface address for protocol	family.	 Following the
		     address assignment, the "initialization" routine for the
		     interface is called.

     SIOCSIFDSTADDR  Set point to point	address	for protocol family and	inter-

     SIOCSIFBRDADDR  Set broadcast address for protocol	family and interface.

     Ioctl() requests to obtain	addresses and requests both to set and re-
     trieve other data are still fully supported and use the ifreq structure:

     SIOCGIFADDR     Get interface address for protocol	family.

     SIOCGIFDSTADDR  Get point to point	address	for protocol family and	inter-

     SIOCGIFBRDADDR  Get broadcast address for protocol	family and interface.

     SIOCSIFCAP	     Attempt to	set the	enabled	capabilities field for the in-
		     terface to	the value of the ifr_reqcap field of the ifreq
		     structure.	 Note that, depending on the particular	inter-
		     face features, some capabilities may appear hard-coded to
		     enabled, or toggling a capability may affect the status
		     of	other ones.  The supported capabilities	field is read-
		     only, and the ifr_curcap field is unused by this call.

     SIOCGIFCAP	     Get the interface capabilities fields.  The values	for
		     supported and enabled capabilities	will be	returned in
		     the ifr_reqcap and	ifr_curcap fields of the ifreq struc-
		     ture, respectively.

     SIOCSIFFLAGS    Set interface flags field.	 If the	interface is marked
		     down, any processes currently routing packets through the
		     interface are notified; some interfaces may be reset so
		     that incoming packets are no longer received.  When
		     marked up again, the interface is reinitialized.

     SIOCGIFFLAGS    Get interface flags.

     SIOCSIFMETRIC   Set interface routing metric.  The	metric is used only by
		     user-level	routers.

     SIOCGIFMETRIC   Get interface metric.

     SIOCIFCREATE    Attempt to	create the specified interface.	 If the	inter-
		     face name is given	without	a unit number the system will
		     attempt to	create a new interface with an arbitrary unit
		     number.  On successful return the ifr_name	field will
		     contain the new interface name.

     SIOCIFDESTROY   Attempt to	destroy	the specified interface.

     There are two requests that make use of a new structure:

     SIOCAIFADDR     An	interface may have more	than one address associated
		     with it in	some protocols.	 This request provides a means
		     to	add additional addresses (or modify characteristics of
		     the primary address if the	default	address	for the	ad-
		     dress family is specified).  Rather than making separate
		     calls to set destination or broadcast addresses, or net-
		     work masks	(now an	integral feature of multiple proto-
		     cols) a separate structure	is used	to specify all three
		     facets simultaneously (see	below).	 One would use a
		     slightly tailored version of this struct specific to each
		     family (replacing each sockaddr by	one of the family-spe-
		     cific type).  Where the sockaddr itself is	larger than
		     the default size, one needs to modify the ioctl() identi-
		     fier itself to include the	total size, as described in

     SIOCDIFADDR     This requests deletes the specified address from the list
		     associated	with an	interface.  It also uses the
		     ifaliasreq	structure to allow for the possibility of pro-
		     tocols allowing multiple masks or destination addresses,
		     and also adopts the convention that specification of the
		     default address means to delete the first address for the
		     interface belonging to the	address	family in which	the
		     original socket was opened.

     SIOCGIFCONF     Get interface configuration list.	This request takes an
		     ifconf structure (see below) as a value-result parameter.
		     The ifc_len field should be initially set to the size of
		     the buffer	pointed	to by ifc_buf.	On return it will con-
		     tain the length, in bytes,	of the configuration list.

     SIOCIFGCLONERS  Get list of clonable interfaces.  This request takes an
		     if_clonereq structure (see	below) as a value-result pa-
		     rameter.  The ifcr_count field should be set to the num-
		     ber of IFNAMSIZ sized strings that	can be fit in the buf-
		     fer pointed to by ifcr_buffer.  On	return,	ifcr_total
		     will be set to the	number of clonable interfaces and the
		     buffer pointed to by ifcr_buffer will be filled with the
		     names of clonable interfaces aligned on IFNAMSIZ bound-

     * Structure used in SIOCAIFCONF request.
     struct ifaliasreq {
	     char    ifra_name[IFNAMSIZ];   /* if name,	e.g. "en0" */
	     struct  sockaddr	     ifra_addr;
	     struct  sockaddr	     ifra_broadaddr;
	     struct  sockaddr	     ifra_mask;

     * Structure used in SIOCGIFCONF request.
     * Used to retrieve	interface configuration
     * for machine (useful for programs	which
     * must know all networks accessible).
     struct ifconf {
	 int   ifc_len;		     /*	size of	associated buffer */
	 union {
	     caddr_t	ifcu_buf;
	     struct	ifreq *ifcu_req;
	 } ifc_ifcu;
     #define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
     #define ifc_req ifc_ifcu.ifcu_req /* array	of structures returned */

     /*	Structure used in SIOCIFGCLONERS request. */
     struct if_clonereq	{
	     int     ifcr_total;     /*	total cloners (out) */
	     int     ifcr_count;     /*	room for this many in user buffer */
	     char    *ifcr_buffer;   /*	buffer for cloner names	*/

     ioctl(2), socket(2), intro(4), config(8), routed(8), ifnet(9)

     The netintro manual appeared in 4.3BSD-Tahoe.

BSD				 June 18, 2004				   BSD


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