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NetBSD 6.1.5 - man page for netintro (netbsd section 4)

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

NAME
     netintro -- introduction to networking facilities

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

DESCRIPTION
     This section is a general introduction to the networking facilities available in the system.
     Documentation in this part of section 4 is broken 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 spe-
     cific network environment.  These services may include packet fragmentation and reassembly,
     routing, addressing, and basic transport.	A protocol family may support multiple methods of
     addressing, though the current protocol implementations do not.  A protocol family normally
     comprises 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 proto-
     col may be accessed either by creating a socket of the appropriate type and protocol family,
     or by requesting the protocol explicitly when creating a socket.  Protocols normally accept
     only one type of address format, usually determined by the addressing structure inherent 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 facili-
     ties or extensions 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 low-
     est layer of the networking subsystem, interacting with the actual transport hardware.  An
     interface may support one or more protocol families and/or address formats.  The SYNOPSIS
     section of each network interface entry gives a sample specification of the related drivers
     for use in providing a system description to the config(1) 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 errors in device operation.

PROTOCOLS
     The system currently supports the Internet protocols and some of the ISO OSI protocols.  Raw
     socket interfaces are provided to the IP protocol layer of the Internet, and to the IDP pro-
     tocol of Xerox NS.  Consult the appropriate manual pages in this section for more informa-
     tion regarding the support for each protocol family.

ADDRESSING
     Associated with each protocol family is an address format.  All network address adhere to a
     general structure, called a sockaddr, described below.  However, each protocol imposes finer
     and more specific structure, generally renaming the variant, which is discussed in the pro-
     tocol 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 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 implementation):

     #define	AF_LOCAL     1	  /* local to host */
     #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 */

ROUTING
     UNIX 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).

INTERFACES
     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 interfaces.  The ioctl(2) 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;
	     int       ifru_metric;
	     void   *ifru_data;
	 } 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	 /* flags */
     #define ifr_metric    ifr_ifru.ifru_metric  /* metric */
     #define ifr_data	   ifr_ifru.ifru_data	 /* for use by interface */
     };

     Calls which are now deprecated are:

     SIOCSIFADDR     Set interface address for protocol family.  Following the address assign-
		     ment, the ``initialization'' routine for the interface is called.

     SIOCSIFDSTADDR  Set point to point address for protocol family and interface.

     SIOCSIFBRDADDR  Set broadcast address for protocol family and interface.

     ioctl(2) requests to obtain addresses and requests both to set and retrieve 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 interface.

     SIOCGIFBRDADDR  Get broadcast address for protocol family and interface.

     SIOCSIFFLAGS    Set interface flags field.  If the interface is marked down, any processes
		     currently routing packets through the interface are notified; some inter-
		     faces 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.

     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 pro-
		     tocols.  This request provides a means to add additional addresses (or mod-
		     ify characteristics of the primary address if the default address for the
		     address family is specified).  Rather than making separate calls to set des-
		     tination or broadcast addresses, or network masks (now an integral feature
		     of multiple protocols) a separate structure, ifaliasreq, is used to specify
		     all three facets simultaneously (see below).  One would use a slightly tai-
		     lored version of this struct specific to each family (replacing each sock-
		     addr by one of the family-specific type).	Where the sockaddr itself is
		     larger than the default size, one needs to modify the ioctl(2) identifier
		     itself to include the total size, as described in ioctl(2).

     SIOCDIFADDR     This requests deletes the specified address from the list associated with an
		     interface.  It also uses the ifaliasreq structure to allow for the possibil-
		     ity of protocols 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.

     Request making use of the ifconf structure:

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

     /*
     * Structure used in SIOC[AD]IFADDR request.
     */
     struct ifaliasreq {
	     char    ifra_name[IFNAMSIZ];   /* if name, e.g. "en0" */
	     struct  sockaddr	     ifra_addr;
	     struct  sockaddr	     ifra_dstaddr;
     #define ifra_broadaddr  ifra_dstaddr
	     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 {
	     void    *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 */
     };

SEE ALSO
     config(1), ioctl(2), socket(2), intro(4), routed(8)

HISTORY
     The netintro manual appeared in 4.3BSD-Tahoe.

BSD					September 7, 2006				      BSD


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