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IFNET(9)	       FreeBSD Kernel Developer's Manual	      IFNET(9)

     ifnet, ifaddr, ifqueue, if_data --	kernel interfaces for manipulating
     network interfaces

     #include <sys/param.h>
     #include <sys/time.h>
     #include <sys/socket.h>
     #include <net/if.h>
     #include <net/if_var.h>
     #include <net/if_types.h>

   Interface Manipulation Functions
     struct ifnet *
     if_alloc(u_char type);

     if_attach(struct ifnet *ifp);

     if_detach(struct ifnet *ifp);

     if_free(struct ifnet *ifp);

     if_free_type(struct ifnet *ifp, u_char type);

     if_down(struct ifnet *ifp);

     ifioctl(struct socket *so,	u_long cmd, caddr_t data, struct thread	*td);

     ifpromisc(struct ifnet *ifp, int pswitch);

     if_allmulti(struct	ifnet *ifp, int	amswitch);

     struct ifnet *
     ifunit(const char *name);

     struct ifnet *
     ifunit_ref(const char *name);

     if_up(struct ifnet	*ifp);

   Interface Address Functions
     struct ifaddr *
     ifaddr_byindex(u_short idx);

     struct ifaddr *
     ifa_ifwithaddr(struct sockaddr *addr);

     struct ifaddr *
     ifa_ifwithdstaddr(struct sockaddr *addr, int fib);

     struct ifaddr *
     ifa_ifwithnet(struct sockaddr *addr, int ignore_ptp, int fib);

     struct ifaddr *
     ifaof_ifpforaddr(struct sockaddr *addr, struct ifnet *ifp);

     ifa_ref(struct ifaddr *ifa);

     ifa_free(struct ifaddr *ifa);

   Interface Multicast Address Functions
     if_addmulti(struct	ifnet *ifp, struct sockaddr *sa,
	 struct	ifmultiaddr **ifmap);

     if_delmulti(struct	ifnet *ifp, struct sockaddr *sa);

     struct ifmultiaddr	*
     if_findmulti(struct ifnet *ifp, struct sockaddr *sa);

   Output queue	macros
     IF_DEQUEUE(struct ifqueue *ifq, struct mbuf *m);

   struct ifnet	Member Functions
     (*if_input)(struct	ifnet *ifp, struct mbuf	*m);

     (*if_output)(struct ifnet *ifp, struct mbuf *m,
	 const struct sockaddr *dst, struct route *ro);

     (*if_start)(struct	ifnet *ifp);

     (*if_transmit)(struct ifnet *ifp, struct mbuf *m);

     (*if_qflush)(struct ifnet *ifp);

     (*if_ioctl)(struct	ifnet *ifp, u_long cmd,	caddr_t	data);

     (*if_init)(void *if_softc);

     (*if_resolvemulti)(struct ifnet *ifp, struct sockaddr **retsa,
	 struct	sockaddr *addr);

   struct ifaddr member	function
     (*ifa_rtrequest)(int cmd, struct rtentry *rt, struct rt_addrinfo *info);

   Global Variables
     extern struct ifnethead ifnet;
     extern int	if_index;
     extern int	ifqmaxlen;

     The kernel	mechanisms for handling	network	interfaces reside primarily in
     the ifnet,	if_data, ifaddr, and ifmultiaddr structures in <net/if.h> and
     <net/if_var.h> and	the functions named above and defined in
     /sys/net/if.c.  Those interfaces which are	intended to be used by user
     programs are defined in <net/if.h>; these include the interface flags,
     the if_data structure, and	the structures defining	the appearance of
     interface-related messages	on the route(4)	routing	socket and in
     sysctl(3).	 The header file <net/if_var.h>	defines	the kernel-internal
     interfaces, including the ifnet, ifaddr, and ifmultiaddr structures and
     the functions which manipulate them.  (A few user programs	will need
     <net/if_var.h> because it is the prerequisite of some other header	file
     like <netinet/if_ether.h>.	 Most references to those two files in partic-
     ular can be replaced by <net/ethernet.h>.)

     The system	keeps a	linked list of interfaces using	the TAILQ macros
     defined in	queue(3); this list is headed by a struct ifnethead called
     ifnet.  The elements of this list are of type struct ifnet, and most ker-
     nel routines which	manipulate interface as	such accept or return pointers
     to	these structures.  Each	interface structure contains an	if_data	struc-
     ture used for statistics and information.	Each interface also has	a
     TAILQ of interface	addresses, described by	ifaddr structures.  An AF_LINK
     address (see link_addr(3))	describing the link layer implemented by the
     interface (if any)	is accessed by the ifaddr_byindex() function or
     if_addr structure.	 (Some trivial interfaces do not provide any link
     layer addresses; this structure, while still present, serves only to
     identify the interface name and index.)

     Finally, those interfaces supporting reception of multicast datagrams
     have a TAILQ of multicast group memberships, described by ifmultiaddr
     structures.  These	memberships are	reference-counted.

     Interfaces	are also associated with an output queue, defined as a struct
     ifqueue; this structure is	used to	hold packets while the interface is in
     the process of sending another.

   The ifnet Structure
     The fields	of struct ifnet	are as follows:

	   if_softc	    (void *) A pointer to the driver's private state
			    block.  (Initialized by driver.)

	   if_l2com	    (void *) A pointer to the common data for the
			    interface's	layer 2	protocol.  (Initialized	by

	   if_vnet	    (struct vnet *) A pointer to the virtual network
			    stack instance.  (Initialized by if_attach().)

	   if_home_vnet	    (struct vnet *) A pointer to the parent virtual
			    network stack, where this struct ifnet originates
			    from.  (Initialized	by if_attach().)

	   if_link	    (TAILQ_ENTRY(ifnet)) queue(3) macro	glue.

	   if_xname	    (char *) The name of the interface,	(e.g.,
			    ``fxp0'' or	``lo0'').  (Initialized	by driver
			    (usually via if_initname()).)

	   if_dname	    (const char	*) The name of the driver.  (Initial-
			    ized by driver (usually via	if_initname()).)

	   if_dunit	    (int) A unique number assigned to each interface
			    managed by a particular driver.  Drivers may
			    choose to set this to IF_DUNIT_NONE	if a unit num-
			    ber	is not associated with the device.  (Initial-
			    ized by driver (usually via	if_initname()).)

	   if_refcount	    (u_int) The	reference count.  (Initialized by

	   if_addrhead	    (struct ifaddrhead)	The head of the	queue(3) TAILQ
			    containing the list	of addresses assigned to this

	   if_pcount	    (int) A count of promiscuous listeners on this
			    interface, used to reference-count the IFF_PROMISC

	   if_carp	    (struct carp_if *) A pointer to the	CARP interface
			    structure, carp(4).	 (Initialized by the driver-
			    specific if_ioctl()	routine.)

	   if_bpf	    (struct bpf_if *) Opaque per-interface data	for
			    the	packet filter, bpf(4).	(Initialized by

	   if_index	    (u_short) A	unique number assigned to each inter-
			    face in sequence as	it is attached.	 This number
			    can	be used	in a struct sockaddr_dl	to refer to a
			    particular interface by index (see link_addr(3)).
			    (Initialized by if_alloc().)

	   if_vlantrunk	    (struct ifvlantrunk	*) A pointer to	802.1Q trunk
			    structure, vlan(4).	 (Initialized by the driver-
			    specific if_ioctl()	routine.)

	   if_flags	    (int) Flags	describing operational parameters of
			    this interface (see	below).	 (Manipulated by
			    generic code.)

	   if_drv_flags	    (int) Flags	describing operational status of this
			    interface (see below).  (Manipulated by driver.)

	   if_capabilities  (int) Flags	describing the capabilities the	inter-
			    face supports (see below).

	   if_capenable	    (int) Flags	describing the enabled capabilities of
			    the	interface (see below).

	   if_linkmib	    (void *) A pointer to an interface-specific	MIB
			    structure exported by ifmib(4).  (Initialized by

	   if_linkmiblen    (size_t) The size of said structure.  (Initialized
			    by driver.)

	   if_data	    (struct if_data) More statistics and information;
			    see	The if_data structure, below.  (Initialized by
			    driver, manipulated	by both	driver and generic

	   if_multiaddrs    (struct ifmultihead) The head of the queue(3)
			    TAILQ containing the list of multicast addresses
			    assigned to	this interface.

	   if_amcount	    (int) A number of multicast	requests on this
			    interface, used to reference-count the
			    IFF_ALLMULTI flag.

	   if_addr	    (struct ifaddr *) A	pointer	to the link-level
			    interface address.	(Initialized by	if_alloc().)

	   if_snd	    (struct ifaltq) The	output queue.  (Manipulated by

			    (const u_int8_t *) A link-level broadcast
			    bytestring for protocols with variable address

	   if_bridge	    (void *) A pointer to the bridge interface struc-
			    ture, if_bridge(4).	 (Initialized by the driver-
			    specific if_ioctl()	routine.)

	   if_label	    (struct label *) A pointer to the MAC Framework
			    label structure, mac(4).  (Initialized by

	   if_afdata	    (void *) An	address	family dependent data region.

			    (int) Used to track	the current state of address
			    family initialization.

	   if_afdata_lock   (struct rwlock) An rwlock(9) lock used to protect
			    if_afdata internals.

	   if_linktask	    (struct task) A taskqueue(9) task scheduled	for
			    link state change events of	the interface.

	   if_addr_lock	    (struct rwlock) An rwlock(9) lock used to protect
			    interface-related address lists.

	   if_clones	    (LIST_ENTRY(ifnet))	queue(3) macro glue for	the
			    list of clonable network interfaces.

	   if_groups	    (TAILQ_HEAD(, ifg_list)) The head of the queue(3)
			    TAILQ containing the list of groups	per interface.

	   if_pf_kif	    (void *) A pointer to the structure	used for
			    interface abstraction by pf(4).

	   if_lagg	    (void *) A pointer to the lagg(4) interface	struc-

	   if_alloctype	    (u_char) The type of the interface as it was at
			    the	time of	its allocation.	 It is used to cache
			    the	type passed to if_alloc(), but unlike if_type,
			    it would not be changed by drivers.

     References	to ifnet structures are	gained by calling the if_ref() func-
     tion and released by calling the if_rele()	function.  They	are used to
     allow kernel code walking global interface	lists to release the ifnet
     lock yet keep the ifnet structure stable.

     There are in addition a number of function	pointers which the driver must
     initialize	to complete its	interface with the generic interface layer:

	   Pass	a packet to an appropriate upper layer as determined from the
	   link-layer header of	the packet.  This routine is to	be called from
	   an interrupt	handler	or used	to emulate reception of	a packet on
	   this	interface.  A single function implementing if_input() can be
	   shared among	multiple drivers utilizing the same link-layer fram-
	   ing,	e.g., Ethernet.

	   Output a packet on interface	ifp, or	queue it on the	output queue
	   if the interface is already active.

	   Transmit a packet on	an interface or	queue it if the	interface is
	   in use.  This function will return ENOBUFS if the devices software
	   and hardware	queues are both	full.  This function must be installed
	   after if_attach() to	override the default implementation.  This
	   function is exposed in order	to allow drivers to manage their own
	   queues and to reduce	the latency caused by a	frequently gratuitous
	   enqueue / dequeue pair to ifq.  The suggested internal software
	   queuing mechanism is	buf_ring.

	   Free	mbufs in internally managed queues when	the interface is
	   marked down.	 This function must be installed after if_attach() to
	   override the	default	implementation.	 This function is exposed in
	   order to allow drivers to manage their own queues and to reduce the
	   latency caused by a frequently gratuitous enqueue / dequeue pair to
	   ifq.	 The suggested internal	software queuing mechanism is

	   Start queued	output on an interface.	 This function is exposed in
	   order to provide for	some interface classes to share	a if_output()
	   among all drivers.  if_start() may only be called when the
	   IFF_DRV_OACTIVE flag	is not set.  (Thus, IFF_DRV_OACTIVE does not
	   literally mean that output is active, but rather that the device's
	   internal output queue is full.) Please note that this function will
	   soon	be deprecated.

	   Process interface-related ioctl(2) requests (defined	in
	   <sys/sockio.h>).  Preliminary processing is done by the generic
	   routine ifioctl() to	check for appropriate privileges, locate the
	   interface being manipulated,	and perform certain generic operations
	   like	twiddling flags	and flushing queues.  See the description of
	   ifioctl() below for more information.

	   Initialize and bring	up the hardware, e.g., reset the chip and
	   enable the receiver unit.  Should mark the interface	running, but

	   Check the requested multicast group membership, addr, for validity,
	   and if necessary compute a link-layer group which corresponds to
	   that	address	which is returned in *retsa.  Returns zero on success,
	   or an error code on failure.

   Interface Flags
     Interface flags are used for a number of different	purposes.  Some	flags
     simply indicate information about the type	of interface and its capabili-
     ties; others are dynamically manipulated to reflect the current state of
     the interface.  Flags of the former kind are marked <S> in	this table;
     the latter	are marked <D>.	 Flags which begin with	``IFF_DRV_'' are
     stored in if_drv_flags; all other flags are stored	in if_flags.

     The macro IFF_CANTCHANGE defines the bits which cannot be set by a	user
     program using the SIOCSIFFLAGS command to ioctl(2); these are indicated
     by	an asterisk (`*') in the following listing.

	   IFF_UP	    <D>	The interface has been configured up by	the
			    user-level code.
	   IFF_BROADCAST    <S*> The interface supports	broadcast.
	   IFF_DEBUG	    <D>	Used to	enable/disable driver debugging	code.
	   IFF_LOOPBACK	    <S>	The interface is a loopback device.
	   IFF_POINTOPOINT  <S*> The interface is point-to-point;
			    ``broadcast'' address is actually the address of
			    the	other end.
	   IFF_DRV_RUNNING  <D*> The interface has been	configured and dynamic
			    resources were successfully	allocated.  Probably
			    only useful	internal to the	interface.
	   IFF_NOARP	    <D>	Disable	network	address	resolution on this
	   IFF_PROMISC	    <D*> This interface	is in promiscuous mode.
	   IFF_PPROMISC	    <D>	This interface is in the permanently promiscu-
			    ous	mode (implies IFF_PROMISC).
	   IFF_ALLMULTI	    <D*> This interface	is in all-multicasts mode
			    (used by multicast routers).
	   IFF_DRV_OACTIVE  <D*> The interface's hardware output queue (if
			    any) is full; output packets are to	be queued.
	   IFF_SIMPLEX	    <S*> The interface cannot hear its own transmis-
	   IFF_LINK2	    <D>	Control	flags for the link layer.  (Currently
			    abused to select among multiple physical layers on
			    some devices.)
	   IFF_MULTICAST    <S*> This interface	supports multicast.
	   IFF_CANTCONFIG   <S*> The interface is not configurable in a	mean-
			    ingful way.	 Primarily useful for IFT_USB inter-
			    faces registered at	the interface list.
	   IFF_MONITOR	    <D>	This interface blocks transmission of packets
			    and	discards incoming packets after	BPF process-
			    ing.  Used to monitor network traffic but not
			    interact with the network in question.
	   IFF_STATICARP    <D>	Used to	enable/disable ARP requests on this
	   IFF_DYING	    <D*> Set when the ifnet structure of this inter-
			    face is being released and still has if_refcount
	   IFF_RENAMING	    <D>	Set when this interface	is being renamed.

   Interface Capabilities Flags
     Interface capabilities are	specialized features an	interface may or may
     not support.  These capabilities are very hardware-specific and allow,
     when enabled, to offload specific network processing to the interface or
     to	offer a	particular feature for use by other kernel parts.

     It	should be stressed that	a capability can be completely uncontrolled
     (i.e., stay always	enabled	with no	way to disable it) or allow limited
     control over itself (e.g.,	depend on another capability's state.)	Such
     peculiarities are determined solely by the	hardware and driver of a par-
     ticular interface.	 Only the driver possesses the knowledge on whether
     and how the interface capabilities	can be controlled.  Consequently,
     capabilities flags	in if_capenable	should never be	modified directly by
     kernel code other than the	interface driver.  The command SIOCSIFCAP to
     ifioctl() is the dedicated	means to attempt altering if_capenable on an
     interface.	 Userland code shall use ioctl(2).

     The following capabilities	are currently supported	by the system:

	   IFCAP_RXCSUM		 This interface	can do checksum	validation on
				 receiving data.  Some interfaces do not have
				 sufficient buffer storage to store frames
				 above a certain MTU-size completely.  The
				 driver	for the	interface might	disable	hard-
				 ware checksum validation if the MTU is	set
				 above the hardcoded limit.

	   IFCAP_TXCSUM		 This interface	can do checksum	calculation on
				 transmitting data.

	   IFCAP_HWCSUM		 A shorthand for (IFCAP_RXCSUM |

	   IFCAP_NETCONS	 This interface	can be a network console.

	   IFCAP_VLAN_MTU	 The vlan(4) driver can	operate	over this
				 interface in software tagging mode without
				 having	to decrease MTU	on vlan(4) interfaces
				 below 1500 bytes.  This implies the ability
				 of this interface to cope with	frames some-
				 what longer than permitted by the Ethernet

	   IFCAP_VLAN_HWTAGGING	 This interface	can do VLAN tagging on output
				 and demultiplex frames	by their VLAN tag on

	   IFCAP_JUMBO_MTU	 This Ethernet interface can transmit and
				 receive frames	up to 9000 bytes long.

	   IFCAP_POLLING	 This interface	supports polling(4).  See
				 below for details.

	   IFCAP_VLAN_HWCSUM	 This interface	can do checksum	calculation on
				 both transmitting and receiving data on
				 vlan(4) interfaces (implies IFCAP_HWCSUM).

	   IFCAP_TSO4		 This Ethernet interface supports TCP4 Segmen-
				 tation	offloading.

	   IFCAP_TSO6		 This Ethernet interface supports TCP6 Segmen-
				 tation	offloading.

	   IFCAP_TSO		 A shorthand for (IFCAP_TSO4 | IFCAP_TSO6).

	   IFCAP_TOE4		 This Ethernet interface supports TCP offload-

	   IFCAP_TOE6		 This Ethernet interface supports TCP6

	   IFCAP_TOE		 A shorthand for (IFCAP_TOE4 | IFCAP_TOE6).

	   IFCAP_WOL_UCAST	 This Ethernet interface supports waking up on
				 any Unicast packet.

	   IFCAP_WOL_MCAST	 This Ethernet interface supports waking up on
				 any Multicast packet.

	   IFCAP_WOL_MAGIC	 This Ethernet interface supports waking up on
				 any Magic packet such as those	sent by

	   IFCAP_WOL		 A shorthand for (IFCAP_WOL_UCAST |

	   IFCAP_TOE4		 This Ethernet interface supports TCP4 Offload

	   IFCAP_TOE6		 This Ethernet interface supports TCP6 Offload

	   IFCAP_TOE		 A shorthand for (IFCAP_TOE4 | IFCAP_TOE6).

	   IFCAP_VLAN_HWFILTER	 This interface	supports frame filtering in
				 hardware on vlan(4) interfaces.

	   IFCAP_VLAN_HWTSO	 This interface	supports TCP Segmentation
				 offloading on vlan(4) interfaces (implies

	   IFCAP_LINKSTATE	 This Ethernet interface supports dynamic link
				 state changes.

     The ability of advanced network interfaces	to offload certain computa-
     tional tasks from the host	CPU to the board is limited mostly to TCP/IP.
     Therefore a separate field	associated with	an interface (see
     ifnet.if_data.ifi_hwassist	below) keeps a detailed	description of its
     enabled capabilities specific to TCP/IP processing.  The TCP/IP module
     consults the field	to see which tasks can be done on an outgoing packet
     by	the interface.	The flags defined for that field are a superset	of
     those for mbuf.m_pkthdr.csum_flags, namely:

	   CSUM_IP	  The interface	will compute IP	checksums.

	   CSUM_TCP	  The interface	will compute TCP checksums.

	   CSUM_UDP	  The interface	will compute UDP checksums.

     An	interface notifies the TCP/IP module about the tasks the former	has
     performed on an incoming packet by	setting	the corresponding flags	in the
     field mbuf.m_pkthdr.csum_flags of the mbuf	chain containing the packet.
     See mbuf(9) for details.

     The capability of a network interface to operate in polling(4) mode
     involves several flags in different global	variables and per-interface
     fields.  The capability flag IFCAP_POLLING	set in interface's
     if_capabilities indicates support for polling(4) on the particular	inter-
     face.  If set in if_capabilities, the same	flag can be marked or cleared
     in	the interface's	if_capenable within ifioctl(), thus initiating switch
     of	the interface to polling(4) mode or interrupt mode, respectively.  The
     actual mode change	is managed by the driver-specific if_ioctl() routine.
     The polling(4) handler returns the	number of packets processed.

   The if_data Structure
     The if_data structure contains statistics and identifying information
     used by management	programs, and which is exported	to user	programs by
     way of the	ifmib(4) branch	of the sysctl(3) MIB.  The following elements
     of	the if_data structure are initialized by the interface and are not
     expected to change	significantly over the course of normal	operation:

	   ifi_type	   (u_char) The	type of	the interface, as defined in
			   <net/if_types.h> and	described below	in the
			   Interface Types section.

	   ifi_physical	   (u_char) Intended to	represent a selection of phys-
			   ical	layers on devices which	support	more than one;
			   never implemented.

	   ifi_addrlen	   (u_char) Length of a	link-layer address on this
			   device, or zero if there are	none.  Used to ini-
			   tialized the	address	length field in	sockaddr_dl
			   structures referring	to this	interface.

	   ifi_hdrlen	   (u_char) Maximum length of any link-layer header
			   which might be prepended by the driver to a packet
			   before transmission.	 The generic code computes the
			   maximum over	all interfaces and uses	that value to
			   influence the placement of data in mbufs to attempt
			   to ensure that there	is always sufficient space to
			   prepend a link-layer	header without allocating an
			   additional mbuf.

	   ifi_datalen	   (u_char) Length of the if_data structure.  Allows
			   some	stabilization of the routing socket ABI	in the
			   face	of increases in	the length of struct ifdata.

	   ifi_mtu	   (u_long) The	maximum	transmission unit of the
			   medium, exclusive of	any link-layer overhead.

	   ifi_metric	   (u_long) A dimensionless metric interpreted by a
			   user-mode routing process.

	   ifi_baudrate	   (u_long) The	line rate of the interface, in bits
			   per second.

	   ifi_hwassist	   (u_long) A detailed interpretation of the capabili-
			   ties	to offload computational tasks for outgoing
			   packets.  The interface driver must keep this field
			   in accord with the current value of if_capenable.

	   ifi_epoch	   (time_t) The	system uptime when interface was
			   attached or the statistics below were reset.	 This
			   is intended to be used to set the SNMP variable
			   ifCounterDiscontinuityTime.	It may also be used to
			   determine if	two successive queries for an inter-
			   face	of the same index have returned	results	for
			   the same interface.

     The structure additionally	contains generic statistics applicable to a
     variety of	different interface types (except as noted, all	members	are of
     type u_long):

	   ifi_link_state  (u_char) The	current	link state of Ethernet inter-
			   faces.  See the Interface Link States section for
			   possible values.

	   ifi_ipackets	   Number of packets received.

	   ifi_ierrors	   Number of receive errors detected (e.g., FCS
			   errors, DMA overruns, etc.).	 More detailed break-
			   downs can often be had by way of a link-specific

	   ifi_opackets	   Number of packets transmitted.

	   ifi_oerrors	   Number of output errors detected (e.g., late	colli-
			   sions, DMA overruns,	etc.).	More detailed break-
			   downs can often be had by way of a link-specific

	   ifi_collisions  Total number	of collisions detected on output for
			   CSMA	interfaces.  (This member is sometimes
			   [ab]used by other types of interfaces for other
			   output error	counts.)

	   ifi_ibytes	   Total traffic received, in bytes.

	   ifi_obytes	   Total traffic transmitted, in bytes.

	   ifi_imcasts	   Number of packets received which were sent by link-
			   layer multicast.

	   ifi_omcasts	   Number of packets sent by link-layer	multicast.

	   ifi_iqdrops	   Number of packets dropped on	input.	Rarely imple-

	   ifi_oqdrops	   Number of packets dropped on	output.

	   ifi_noproto	   Number of packets received for unknown network-
			   layer protocol.

	   ifi_lastchange  (struct timeval) The	time of	the last administra-
			   tive	change to the interface	(as required for

   Interface Types
     The header	file <net/if_types.h> defines symbolic constants for a number
     of	different types	of interfaces.	The most common	are:

	   IFT_OTHER	    none of the	following
	   IFT_ETHER	    Ethernet
	   IFT_ISO88023	    ISO	8802-3 CSMA/CD
	   IFT_ISO88024	    ISO	8802-4 Token Bus
	   IFT_ISO88025	    ISO	8802-5 Token Ring
	   IFT_ISO88026	    ISO	8802-6 DQDB MAN
	   IFT_PPP	    Internet Point-to-Point Protocol (ppp(8))
	   IFT_LOOP	    The	loopback (lo(4)) interface
	   IFT_SLIP	    Serial Line	IP
	   IFT_PARA	    Parallel-port IP (``PLIP'')
	   IFT_ATM	    Asynchronous Transfer Mode
	   IFT_USB	    USB	Interface

   Interface Link States
     The following link	states are currently defined:

	   LINK_STATE_UNKNOWN  The link	is in an invalid or unknown state.
	   LINK_STATE_DOWN     The link	is down.
	   LINK_STATE_UP       The link	is up.

   The ifaddr Structure
     Every interface is	associated with	a list (or, rather, a TAILQ) of
     addresses,	rooted at the interface	structure's if_addrhead	member.	 The
     first element in this list	is always an AF_LINK address representing the
     interface itself; multi-access network drivers should complete this
     structure by filling in their link-layer addresses	after calling
     if_attach().  Other members of the	structure represent network-layer
     addresses which have been configured by means of the SIOCAIFADDR command
     to	ioctl(2), called on a socket of	the appropriate	protocol family.  The
     elements of this list consist of ifaddr structures.  Most protocols will
     declare their own protocol-specific interface address structures, but all
     begin with	a struct ifaddr	which provides the most-commonly-needed	func-
     tionality across all protocols.  Interface	addresses are reference-

     The members of struct ifaddr are as follows:

	   ifa_addr	  (struct sockaddr *) The local	address	of the inter-

	   ifa_dstaddr	  (struct sockaddr *) The remote address of point-to-
			  point	interfaces, and	the broadcast address of
			  broadcast interfaces.	 (ifa_broadaddr	is a macro for

	   ifa_netmask	  (struct sockaddr *) The network mask for multi-
			  access interfaces, and the confusion generator for
			  point-to-point interfaces.

	   ifa_ifp	  (struct ifnet	*) A link back to the interface	struc-

	   ifa_link	  (TAILQ_ENTRY(ifaddr))	queue(3) glue for list of
			  addresses on each interface.

	   ifa_rtrequest  See below.

	   ifa_flags	  (u_short) Some of the	flags which would be used for
			  a route representing this address in the route ta-

	   ifa_refcnt	  (short) The reference	count.

     References	to ifaddr structures are gained	by calling the ifa_ref() func-
     tion and released by calling the ifa_free() function.

     ifa_rtrequest() is	a pointer to a function	which receives callouts	from
     the routing code (rtrequest()) to perform link-layer-specific actions
     upon requests to add, or delete routes.  The cmd argument indicates the
     request in	question: RTM_ADD, or RTM_DELETE.  The rt argument is the
     route in question;	the info argument contains the specific	destination
     being manipulated.

     The functions provided by the generic interface code can be divided into
     two groups: those which manipulate	interfaces, and	those which manipulate
     interface addresses.  In addition to these	functions, there may also be
     link-layer	support	routines which are used	by a number of drivers imple-
     menting a specific	link layer over	different hardware; see	the documenta-
     tion for that link	layer for more details.

   The ifmultiaddr Structure
     Every multicast-capable interface is associated with a list of multicast
     group memberships,	which indicate at a low	level which link-layer multi-
     cast addresses (if	any) should be accepted, and at	a high level, in which
     network-layer multicast groups a user process has expressed interest.

     The elements of the structure are as follows:

	   ifma_link	  (LIST_ENTRY(ifmultiaddr)) queue(3) macro glue.

	   ifma_addr	  (struct sockaddr *) A	pointer	to the address which
			  this record represents.  The memberships for various
			  address families are stored in arbitrary order.

	   ifma_lladdr	  (struct sockaddr *) A	pointer	to the link-layer mul-
			  ticast address, if any, to which the network-layer
			  multicast address in ifma_addr is mapped, else a
			  null pointer.	 If this element is non-nil, this mem-
			  bership also holds an	invisible reference to another
			  membership for that link-layer address.

	   ifma_refcount  (u_int) A reference count of requests	for this par-
			  ticular membership.

   Interface Manipulation Functions
	   Allocate and	initialize struct ifnet.  Initialization includes the
	   allocation of an interface index and	may include the	allocation of
	   a type specific structure in	if_l2com.

	   Link	the specified interface	ifp into the list of network inter-
	   faces.  Also	initialize the list of addresses on that interface,
	   and create a	link-layer ifaddr structure to be the first element in
	   that	list.  (A pointer to this address structure is saved in	the
	   ifnet structure and is accessed by the ifaddr_byindex() function.)
	   The ifp must	have been allocated by if_alloc().

	   Shut	down and unlink	the specified ifp from the interface list.

	   Free	the given ifp back to the system.  The interface must have
	   been	previously detached if it was ever attached.

	   Identical to	if_free() except that the given	type is	used to	free
	   if_l2com instead of the type	in if_type.  This is intended for use
	   with	drivers	that change their interface type.

	   Mark	the interface ifp as down (i.e., IFF_UP	is not set), flush its
	   output queue, notify	protocols of the transition, and generate a
	   message from	the route(4) routing socket.

	   Mark	the interface ifp as up, notify	protocols of the transition,
	   and generate	a message from the route(4) routing socket.

	   Add or remove a promiscuous reference to ifp.  If pswitch is	true,
	   add a reference; if it is false, remove a reference.	 On reference
	   count transitions from zero to one and one to zero, set the
	   IFF_PROMISC flag appropriately and call if_ioctl() to set up	the
	   interface in	the desired mode.

	   As ifpromisc(), but for the all-multicasts (IFF_ALLMULTI) flag
	   instead of the promiscuous flag.

	   Return an ifnet pointer for the interface named name.

	   Return a reference-counted (via ifa_ref()) ifnet pointer for	the
	   interface named name.  This is the preferred	function over
	   ifunit().  The caller is responsible	for releasing the reference
	   with	if_rele() when it is finished with the ifnet.

	   Process the ioctl request cmd, issued on socket so by thread	td,
	   with	data parameter data.  This is the main routine for handling
	   all interface configuration requests	from user mode.	 It is ordi-
	   narily only called from the socket-layer ioctl(2) handler, and only
	   for commands	with class `i'.	 Any unrecognized commands will	be
	   passed down to socket so's protocol for further interpretation.
	   The following commands are handled by ifioctl():

		 SIOCGIFCONF	 Get interface configuration.  (No call-down
				 to driver.)

		 SIOCSIFNAME	 Set the interface name.  RTM_IFANNOUNCE
				 departure and arrival messages	are sent so
				 that routing code that	relies on the inter-
				 face name will	update its interface list.
				 Caller	must have appropriate privilege.  (No
				 call-down to driver.)
		 SIOCGIFPHYS	 Get interface capabilities, FIB, flags, met-
				 ric, MTU, medium selection.  (No call-down to

		 SIOCSIFCAP	 Enable	or disable interface capabilities.
				 Caller	must have appropriate privilege.
				 Before	a call to the driver-specific
				 if_ioctl() routine, the requested mask	for
				 enabled capabilities is checked against the
				 mask of capabilities supported	by the inter-
				 face, if_capabilities.	 Requesting to enable
				 an unsupported	capability is invalid.	The
				 rest is supposed to be	done by	the driver,
				 which includes	updating if_capenable and
				 if_data.ifi_hwassist appropriately.

		 SIOCSIFFIB	 Sets interface	FIB.  Caller must have appro-
				 priate	privilege.  FIB	values start at	0 and
				 values	greater	or equals than net.fibs	are
				 considered invalid.
		 SIOCSIFFLAGS	 Change	interface flags.  Caller must have
				 appropriate privilege.	 If a change to	the
				 IFF_UP	flag is	requested, if_up() or
				 if_down() is called as	appropriate.  Flags
				 listed	in IFF_CANTCHANGE are masked off, and
				 the field if_flags in the interface structure
				 is updated.  Finally, the driver if_ioctl()
				 routine is called to perform any setup

		 SIOCSIFPHYS	 Change	interface metric or medium.  Caller
				 must have appropriate privilege.

		 SIOCSIFMTU	 Change	interface MTU.	Caller must have
				 appropriate privilege.	 MTU values less than
				 72 or greater than 65535 are considered
				 invalid.  The driver if_ioctl() routine is
				 called	to implement the change; it is respon-
				 sible for any additional sanity checking and
				 for actually modifying	the MTU	in the inter-
				 face structure.

		 SIOCDELMULTI	 Add or	delete permanent multicast group mem-
				 berships on the interface.  Caller must have
				 appropriate privilege.	 The if_addmulti() or
				 if_delmulti() function	is called to perform
				 the operation;	qq.v.

		 SIOCDIFADDR	 The socket's protocol control routine is
				 called	to implement the requested action.

     if_down(),	ifioctl(), ifpromisc(),	and if_up() must be called at splnet()
     or	higher.

   Interface Address Functions
     Several functions exist to	look up	an interface address structure given
     an	address.  ifa_ifwithaddr() returns an interface	address	with either a
     local address or a	broadcast address precisely matching the parameter
     addr.  ifa_ifwithdstaddr()	returns	an interface address for a point-to-
     point interface whose remote (``destination'') address is addr and	a fib
     is	fib.  If fib is	RT_ALL_FIBS, then the first interface address matching
     addr will be returned.

     ifa_ifwithnet() returns the most specific interface address which matches
     the specified address, addr, subject to its configured netmask, or	a
     point-to-point interface address whose remote address is addr if one is
     found.  If	ignore_ptp is true, skip point-to-point	interface addresses.
     The fib parameter is handled the same way as by ifa_ifwithdstaddr().

     ifaof_ifpforaddr()	returns	the most specific address configured on	inter-
     face ifp which matches address addr, subject to its configured netmask.
     If	the interface is point-to-point, only an interface address whose
     remote address is precisely addr will be returned.

     ifaddr_byindex() returns the link-level address of	the interface with the
     given index idx.

     All of these functions return a null pointer if no	such address can be

   Interface Multicast Address Functions
     The if_addmulti(),	if_delmulti(), and if_findmulti() functions provide
     support for requesting and	relinquishing multicast	group memberships, and
     for querying an interface's membership list, respectively.	 The
     if_addmulti() function takes a pointer to an interface, ifp, and a
     generic address, sa.  It also takes a pointer to a	struct ifmultiaddr *
     which is filled in	on successful return with the address of the group
     membership	control	block.	The if_addmulti() function performs the	fol-
     lowing four-step process:

	   1.	Call the interface's if_resolvemulti() entry point to deter-
		mine the link-layer address, if	any, corresponding to this
		membership request, and	also to	give the link layer an oppor-
		tunity to veto this membership request should it so desire.

	   2.	Check the interface's group membership list for	a pre-existing
		membership for this group.  If one is not found, allocate a
		new one; if one	is, increment its reference count.

	   3.	If the if_resolvemulti() routine returned a link-layer address
		corresponding to the group, repeat the previous	step for that
		address	as well.

	   4.	If the interface's multicast address filter needs to be
		changed	because	a new membership was added, call the inter-
		face's if_ioctl() routine (with	a cmd argument of
		SIOCADDMULTI) to request that it do so.

     The if_delmulti() function, given an interface ifp	and an address,	sa,
     reverses this process.  Both functions return zero	on success, or a stan-
     dard error	number on failure.

     The if_findmulti()	function examines the membership list of interface ifp
     for an address matching sa, and returns a pointer to that struct
     ifmultiaddr if one	is found, else it returns a null pointer.

     ioctl(2), link_addr(3), queue(3), sysctl(3), bpf(4), ifmib(4), lo(4),
     netintro(4), polling(4), config(8), ppp(8), mbuf(9), rtentry(9)

     Gary R. Wright and	W. Richard Stevens, TCP/IP Illustrated,	Vol. 2,
     Addison-Wesley, ISBN 0-201-63354-X.

     This manual page was written by Garrett A.	Wollman.

FreeBSD	Ports 11.2	       December	6, 2017		    FreeBSD Ports 11.2


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