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intro(4n) [ultrix man page]

intro(4n)																 intro(4n)

       networking - introduction to networking facilities

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

       This  section  briefly  describes  the networking facilities available in the system.  Documentation in this part of Section 4 is broken up
       into three areas: protocol families, protocols, and ``network interfaces''.  Entries describing a protocol family are marked ``4f'',  while
       entries describing protocol use are marked ``4p''.  Hardware support for network interfaces is found among the standard ``4'' entries.

       All  network protocols are associated with a specific protocol family.  A protocol family provides basic services to the protocol implemen-
       tation to allow it to function within a specific network environment.  These services can  include  packet  fragmentation  and  reassembly,
       routing, addressing, and basic transport.  A protocol family can support multiple methods of addressing, though the current protocol imple-
       mentations do not.  A protocol family normally comprises a number of protocols, one per socket type.  It is not required  that  a  protocol
       family support all socket types.  A protocol family can contain multiple protocols supporting the same socket abstraction.

       A  protocol  supports  one  of  the  socket abstractions detailed in A specific protocol can 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 nonstandard facilities or extensions to a mechanism.  For example, a protocol sup-
       porting 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 make up the lowest layer of the networking subsystem, interacting
       with the actual transport hardware.  An interface may support one or more protocol families or address formats.	The SYNTAX section of each
       network interface entry gives a sample specification of the related drivers for use in providing a system description  to  The  DIAGNOSTICS
       section lists messages that may appear on the console and in the system error log file due to errors in device operation.

       Associated with each protocol family is an address format.  The following address formats are used by the system:
       #define AF_UNIX	  1  /* local to host (pipes, portals) */
       #define AF_INET	  2  /* internetwork: UDP, TCP, etc. */
       #define AF_IMPLINK 3  /* arpanet imp addresses */

       The  network  facilities provide limited packet routing.  A simple set of data structures make up a ``routing table'' used in selecting the
       appropriate network interface when transmitting packets.  This table contains a single entry for each route to a specific network or  host.
       A  user	process,  the routing daemon, maintains this data base with the aid of two socket-specific commands, SIOCADDRT and SIOCDELRT.  The
       commands allow the addition and deletion of a single routing table entry.  Routing table manipulations can only be  carried  out  by  supe-

       A routing table entry has the following form, as defined in <net/route.h>:
       struct rtentry {
	       u_long  rt_hash;
	       struct  sockaddr rt_dst;
	       struct  sockaddr rt_gateway;
	       short   rt_flags;
	       short   rt_refcnt;
	       u_long  rt_use;
	       struct  rtentry *rt_next;
	       struct  ifnet *rt_ifp;
       with rt_flags defined from,
       #define	RTF_UP	    0x1   /* route usable */
       #define	RTF_GATEWAY 0x2   /* destination is a gateway */
       #define	RTF_HOST    0x4   /* host entry (net otherwise) */
       Routing table entries come in three types: for a specific host, for all hosts on a specific network, and for any destination not matched by
       entries of the first two types (a wildcard route).  When the system is booted, each network interface autoconfigured installs a routing ta-
       ble  entry  when it wishes to have packets sent through it.  Normally, the interface specifies the route through it is a ``direct'' connec-
       tion to the destination host or network.  If the route is direct, the transport layer of a protocol family usually requests the	packet	be
       sent to the same host specified in the packet.  Otherwise, the interface may be requested to address the packet to an entity different from
       the eventual recipient (that is, the packet is forwarded).

       Routing table entries installed by a user process cannot specify the hash, reference count, use, or interface fields; these are	filled	in
       by  the	routing  routines.   If  a  route  is  in  use when it is deleted (rt_refcnt is nonzero), the resources associated with it are not
       reclaimed until further references to it are released.

       The routing code returns EEXIST if requested to duplicate an existing entry, ESRCH if requested to delete a nonexistent entry,  or  ENOBUFS
       if insufficient resources were available to install a new route.

       User processes read the routing tables through the device.

       The  rt_use field contains the number of packets sent along the route.  This value is used to select among multiple routes to the same des-
       tination.  When multiple routes to the same destination exist, the least used route is selected.

       A wildcard routing entry is specified with a zero destination address value.  Wildcard routes are used only when the system fails to find a
       route  to  the  destination host and network.  The combination of wildcard routes and routing redirects can provide an economical mechanism
       for routing traffic.

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

       At  boot  time,	each interface that has underlying hardware support makes itself known to the system during the autoconfiguration process.
       Once the interface has acquired its address, it is expected to install a routing table entry so that messages can  be  routed  through  it.
       Most  interfaces require some part of their address specified with an SIOCSIFADDR ioctl before they allow traffic to flow through them.	On
       interfaces where the network-link layer address mapping is static, only the network number is taken from the ioctl; the remainder is  found
       in  a hardware-specific manner.	On interfaces that provide dynamic network-link layer address mapping facilities (for example, 10Mb/s Eth-
       ernets), the entire address specified in the ioctl is used.

       The following calls may be used to manipulate network interfaces.  Unless specified otherwise, the request takes an ifrequest structure	as
       its parameter.  This structure has the form:
       struct  ifreq {
	 char	 ifr_name[16];	 /* name of interface (e.g. "ec0") */
	 union {
		struct	  sockaddr ifru_addr;
		struct	  sockaddr ifru_dstaddr;
		short	  ifru_flags;
	    } ifr_ifru;
       #define ifr_addr    ifr_ifru.ifru_addr	 /* address */
       #define ifr_dstaddr ifr_ifru.ifru_dstaddr /* end of p-to-p link */
       #define ifr_flags   ifr_ifru.ifru_flags	 /* flags */

	      Set interface address.  Following the address assignment, the ``initialization'' routine for the interface is called.

	      Get interface address.

	      Set point-to-point address for interface.

	      Get point-to-point address for interface.

	      Read or set ownership and state of a device.

	      Set interface flags field.  If the interface is marked down, any processes currently routing packets through the interface are noti-

	      Get interface flags.

	      Get interface configuration list.  This request takes an ifconf structure (see SIOCSIFBRDADDR) 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 contain the length, in
	      bytes, of the configuration list.

	      Get network address mask.

	      Set network address mask.

	      Get broadcast address associated with network interface.

	      Set broadcast address associated with network interface.
	       * 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 */
	      The following is the structure used in an SIOCSTATE request to set device state and ownership.
	      struct ifstate {
	       char    ifr_name[IFNAMSIZ]; /* if name, e.g. "dmv0" */
	       u_short if_family;	   /* current family ownership */
	       u_short if_next_family;	   /* next family ownership */
	       u_short if_mode:3,	   /* mode of device */
		       if_ustate:1,	   /* user requested state */
		       if_nomuxhdr:1,	   /* if set, omit mux header */
		       if_dstate:4,	   /* current state of device */
		       if_xferctl:1,	   /* xfer control to nxt family */
		       if_rdstate:1,	   /* read current state */
		       if_wrstate:1	   /* set current state */

See Also
       socket(2), ioctl(2), intro(4), config(8), routed(8c)

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