xref: /freebsd/share/man/man9/ifnet.9 (revision 38f0b757fd84d17d0fc24739a7cda160c4516d81)
1.\" -*- Nroff -*-
2.\" Copyright 1996, 1997 Massachusetts Institute of Technology
3.\"
4.\" Permission to use, copy, modify, and distribute this software and
5.\" its documentation for any purpose and without fee is hereby
6.\" granted, provided that both the above copyright notice and this
7.\" permission notice appear in all copies, that both the above
8.\" copyright notice and this permission notice appear in all
9.\" supporting documentation, and that the name of M.I.T. not be used
10.\" in advertising or publicity pertaining to distribution of the
11.\" software without specific, written prior permission.  M.I.T. makes
12.\" no representations about the suitability of this software for any
13.\" purpose.  It is provided "as is" without express or implied
14.\" warranty.
15.\"
16.\" THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''.  M.I.T. DISCLAIMS
17.\" ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
18.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
19.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
20.\" SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
23.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
24.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
25.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
26.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27.\" SUCH DAMAGE.
28.\"
29.\" $FreeBSD$
30.\"
31.Dd November 5, 2013
32.Dt IFNET 9
33.Os
34.Sh NAME
35.Nm ifnet ,
36.Nm ifaddr ,
37.Nm ifqueue ,
38.Nm if_data
39.Nd kernel interfaces for manipulating network interfaces
40.Sh SYNOPSIS
41.In sys/param.h
42.In sys/time.h
43.In sys/socket.h
44.In net/if.h
45.In net/if_var.h
46.In net/if_types.h
47.\"
48.Ss "Interface Manipulation Functions"
49.Ft "struct ifnet *"
50.Fn if_alloc "u_char type"
51.Ft void
52.Fn if_attach "struct ifnet *ifp"
53.Ft void
54.Fn if_detach "struct ifnet *ifp"
55.Ft void
56.Fn if_free "struct ifnet *ifp"
57.Ft void
58.Fn if_free_type "struct ifnet *ifp" "u_char type"
59.Ft void
60.Fn if_down "struct ifnet *ifp"
61.Ft int
62.Fn ifioctl "struct socket *so" "u_long cmd" "caddr_t data" "struct thread *td"
63.Ft int
64.Fn ifpromisc "struct ifnet *ifp" "int pswitch"
65.Ft int
66.Fn if_allmulti "struct ifnet *ifp" "int amswitch"
67.Ft "struct ifnet *"
68.Fn ifunit "const char *name"
69.Ft "struct ifnet *"
70.Fn ifunit_ref "const char *name"
71.Ft void
72.Fn if_up "struct ifnet *ifp"
73.\"
74.Ss "Interface Address Functions"
75.Ft "struct ifaddr *"
76.Fn ifaddr_byindex "u_short idx"
77.Ft "struct ifaddr *"
78.Fn ifa_ifwithaddr "struct sockaddr *addr"
79.Ft "struct ifaddr *"
80.Fn ifa_ifwithdstaddr "struct sockaddr *addr"
81.Ft "struct ifaddr *"
82.Fn ifa_ifwithnet "struct sockaddr *addr" "int ignore_ptp"
83.Ft "struct ifaddr *"
84.Fn ifaof_ifpforaddr "struct sockaddr *addr" "struct ifnet *ifp"
85.Ft void
86.Fn ifa_ref "struct ifaddr *ifa"
87.Ft void
88.Fn ifa_free "struct ifaddr *ifa"
89.\"
90.Ss "Interface Multicast Address Functions"
91.Ft int
92.Fn if_addmulti "struct ifnet *ifp" "struct sockaddr *sa" "struct ifmultiaddr **ifmap"
93.Ft int
94.Fn if_delmulti "struct ifnet *ifp" "struct sockaddr *sa"
95.Ft "struct ifmultiaddr *"
96.Fn if_findmulti "struct ifnet *ifp" "struct sockaddr *sa"
97.Ss "Output queue macros"
98.Fn IF_DEQUEUE "struct ifqueue *ifq" "struct mbuf *m"
99.\"
100.Ss "struct ifnet Member Functions"
101.Ft void
102.Fn \*(lp*if_input\*(rp "struct ifnet *ifp" "struct mbuf *m"
103.Ft int
104.Fo \*(lp*if_output\*(rp
105.Fa "struct ifnet *ifp" "struct mbuf *m"
106.Fa "const struct sockaddr *dst" "struct route *ro"
107.Fc
108.Ft void
109.Fn \*(lp*if_start\*(rp "struct ifnet *ifp"
110.Ft int
111.Fn \*(lp*if_transmit\*(rp "struct ifnet *ifp" "struct mbuf *m"
112.Ft void
113.Fn \*(lp*if_qflush\*(rp "struct ifnet *ifp"
114.Ft int
115.Fn \*(lp*if_ioctl\*(rp "struct ifnet *ifp" "u_long cmd" "caddr_t data"
116.Ft void
117.Fn \*(lp*if_init\*(rp "void *if_softc"
118.Ft int
119.Fo \*(lp*if_resolvemulti\*(rp
120.Fa "struct ifnet *ifp" "struct sockaddr **retsa" "struct sockaddr *addr"
121.Fc
122.Ss "struct ifaddr member function"
123.Ft void
124.Fo \*(lp*ifa_rtrequest\*(rp
125.Fa "int cmd" "struct rtentry *rt" "struct rt_addrinfo *info"
126.Fc
127.\"
128.Ss "Global Variables"
129.Vt extern struct ifnethead ifnet ;
130.\" extern struct ifindex_entry *ifindex_table ;
131.Vt extern int if_index ;
132.Vt extern int ifqmaxlen ;
133.Sh DATA STRUCTURES
134The kernel mechanisms for handling network interfaces reside primarily
135in the
136.Vt ifnet , if_data , ifaddr ,
137and
138.Vt ifmultiaddr
139structures in
140.In net/if.h
141and
142.In net/if_var.h
143and the functions named above and defined in
144.Pa /sys/net/if.c .
145Those interfaces which are intended to be used by user programs
146are defined in
147.In net/if.h ;
148these include the interface flags, the
149.Vt if_data
150structure, and the structures defining the appearance of
151interface-related messages on the
152.Xr route 4
153routing socket and in
154.Xr sysctl 3 .
155The header file
156.In net/if_var.h
157defines the kernel-internal interfaces, including the
158.Vt ifnet , ifaddr ,
159and
160.Vt ifmultiaddr
161structures and the functions which manipulate them.
162(A few user programs will need
163.In net/if_var.h
164because it is the prerequisite of some other header file like
165.In netinet/if_ether.h .
166Most references to those two files in particular can be replaced by
167.In net/ethernet.h . )
168.Pp
169The system keeps a linked list of interfaces using the
170.Li TAILQ
171macros defined in
172.Xr queue 3 ;
173this list is headed by a
174.Vt "struct ifnethead"
175called
176.Va ifnet .
177The elements of this list are of type
178.Vt "struct ifnet" ,
179and most kernel routines which manipulate interface as such accept or
180return pointers to these structures.
181Each interface structure
182contains an
183.Vt if_data
184structure used for statistics and information.
185Each interface also has a
186.Li TAILQ
187of interface addresses, described by
188.Vt ifaddr
189structures.
190An
191.Dv AF_LINK
192address
193(see
194.Xr link_addr 3 )
195describing the link layer implemented by the interface (if any)
196is accessed by the
197.Fn ifaddr_byindex
198function or
199.Va if_addr
200structure.
201(Some trivial interfaces do not provide any link layer addresses;
202this structure, while still present, serves only to identify the
203interface name and index.)
204.Pp
205Finally, those interfaces supporting reception of multicast datagrams
206have a
207.Li TAILQ
208of multicast group memberships, described by
209.Vt ifmultiaddr
210structures.
211These memberships are reference-counted.
212.Pp
213Interfaces are also associated with an output queue, defined as a
214.Vt "struct ifqueue" ;
215this structure is used to hold packets while the interface is in the
216process of sending another.
217.Pp
218.Ss The Vt ifnet Ss structure
219The fields of
220.Vt "struct ifnet"
221are as follows:
222.Bl -tag -width ".Va if_capabilities" -offset indent
223.It Va if_softc
224.Pq Vt "void *"
225A pointer to the driver's private state block.
226(Initialized by driver.)
227.It Va if_l2com
228.Pq Vt "void *"
229A pointer to the common data for the interface's layer 2 protocol.
230(Initialized by
231.Fn if_alloc . )
232.It Va if_vnet
233.Pq Vt "struct vnet *"
234A pointer to the virtual network stack instance.
235(Initialized by
236.Fn if_attach . )
237.It Va if_home_vnet
238.Pq Vt "struct vnet *"
239A pointer to the parent virtual network stack, where this
240.Vt "struct ifnet"
241originates from.
242(Initialized by
243.Fn if_attach . )
244.It Va if_link
245.Pq Fn TAILQ_ENTRY ifnet
246.Xr queue 3
247macro glue.
248.It Va if_xname
249.Pq Vt "char *"
250The name of the interface,
251(e.g.,
252.Dq Li fxp0
253or
254.Dq Li lo0 ) .
255(Initialized by driver
256(usually via
257.Fn if_initname ) . )
258.It Va if_dname
259.Pq Vt "const char *"
260The name of the driver.
261(Initialized by driver
262(usually via
263.Fn if_initname ) . )
264.It Va if_dunit
265.Pq Vt int
266A unique number assigned to each interface managed by a particular
267driver.
268Drivers may choose to set this to
269.Dv IF_DUNIT_NONE
270if a unit number is not associated with the device.
271(Initialized by driver
272(usually via
273.Fn if_initname ) . )
274.It Va if_refcount
275.Pq Vt u_int
276The reference count.
277(Initialized by
278.Fn if_alloc . )
279.It Va if_addrhead
280.Pq Vt "struct ifaddrhead"
281The head of the
282.Xr queue 3
283.Li TAILQ
284containing the list of addresses assigned to this interface.
285.It Va if_pcount
286.Pq Vt int
287A count of promiscuous listeners on this interface, used to
288reference-count the
289.Dv IFF_PROMISC
290flag.
291.It Va if_carp
292.Pq Vt "struct carp_if *"
293A pointer to the CARP interface structure,
294.Xr carp 4 .
295(Initialized by the driver-specific
296.Fn if_ioctl
297routine.)
298.It Va if_bpf
299.Pq Vt "struct bpf_if *"
300Opaque per-interface data for the packet filter,
301.Xr bpf 4 .
302(Initialized by
303.Fn bpf_attach . )
304.It Va if_index
305.Pq Vt u_short
306A unique number assigned to each interface in sequence as it is
307attached.
308This number can be used in a
309.Vt "struct sockaddr_dl"
310to refer to a particular interface by index
311(see
312.Xr link_addr 3 ) .
313(Initialized by
314.Fn if_alloc . )
315.It Va if_vlantrunk
316.Pq Vt struct ifvlantrunk *
317A pointer to 802.1Q trunk structure,
318.Xr vlan 4 .
319(Initialized by the driver-specific
320.Fn if_ioctl
321routine.)
322.It Va if_flags
323.Pq Vt int
324Flags describing operational parameters of this interface (see below).
325(Manipulated by generic code.)
326.It Va if_drv_flags
327.Pq Vt int
328Flags describing operational status of this interface (see below).
329(Manipulated by driver.)
330.It Va if_capabilities
331.Pq Vt int
332Flags describing the capabilities the interface supports (see below).
333.It Va if_capenable
334.Pq Vt int
335Flags describing the enabled capabilities of the interface (see below).
336.It Va if_linkmib
337.Pq Vt "void *"
338A pointer to an interface-specific MIB structure exported by
339.Xr ifmib 4 .
340(Initialized by driver.)
341.It Va if_linkmiblen
342.Pq Vt size_t
343The size of said structure.
344(Initialized by driver.)
345.It Va if_data
346.Pq Vt "struct if_data"
347More statistics and information; see
348.Sx "The if_data structure" ,
349below.
350(Initialized by driver, manipulated by both driver and generic
351code.)
352.It Va if_multiaddrs
353.Pq Vt struct ifmultihead
354The head of the
355.Xr queue 3
356.Li TAILQ
357containing the list of multicast addresses assigned to this interface.
358.It Va if_amcount
359.Pq Vt int
360A number of multicast requests on this interface, used to
361reference-count the
362.Dv IFF_ALLMULTI
363flag.
364.It Va if_addr
365.Pq Vt "struct ifaddr *"
366A pointer to the link-level interface address.
367(Initialized by
368.Fn if_alloc . )
369.\" .It Va if_llsoftc
370.\" .Pq Vt "void *"
371.\" The purpose of the field is unclear.
372.It Va if_snd
373.Pq Vt "struct ifaltq"
374The output queue.
375(Manipulated by driver.)
376.It Va if_broadcastaddr
377.Pq Vt "const u_int8_t *"
378A link-level broadcast bytestring for protocols with variable address
379length.
380.It Va if_bridge
381.Pq Vt "void *"
382A pointer to the bridge interface structure,
383.Xr if_bridge 4 .
384(Initialized by the driver-specific
385.Fn if_ioctl
386routine.)
387.It Va if_label
388.Pq Vt "struct label *"
389A pointer to the MAC Framework label structure,
390.Xr mac 4 .
391(Initialized by
392.Fn if_alloc . )
393.It Va if_afdata
394.Pq Vt "void *"
395An address family dependent data region.
396.It Va if_afdata_initialized
397.Pq Vt int
398Used to track the current state of address family initialization.
399.It Va if_afdata_lock
400.Pq Vt "struct rwlock"
401An
402.Xr rwlock 9
403lock used to protect
404.Va if_afdata
405internals.
406.It Va if_linktask
407.Pq Vt "struct task"
408A
409.Xr taskqueue 9
410task scheduled for link state change events of the interface.
411.It Va if_addr_lock
412.Pq Vt "struct rwlock"
413An
414.Xr rwlock 9
415lock used to protect interface-related address lists.
416.It Va if_clones
417.Pq Fn LIST_ENTRY ifnet
418.Xr queue 3
419macro glue for the list of clonable network interfaces.
420.It Va if_groups
421.Pq Fn TAILQ_HEAD ", ifg_list"
422The head of the
423.Xr queue 3
424.Li TAILQ
425containing the list of groups per interface.
426.It Va if_pf_kif
427.Pq Vt "void *"
428A pointer to the structure used for interface abstraction by
429.Xr pf 4 .
430.It Va if_lagg
431.Pq Vt "void *"
432A pointer to the
433.Xr lagg 4
434interface structure.
435.It Va if_alloctype
436.Pq Vt u_char
437The type of the interface as it was at the time of its allocation.
438It is used to cache the type passed to
439.Fn if_alloc ,
440but unlike
441.Va if_type ,
442it would not be changed by drivers.
443.El
444.Pp
445References to
446.Vt ifnet
447structures are gained by calling the
448.Fn if_ref
449function and released by calling the
450.Fn if_rele
451function.
452They are used to allow kernel code walking global interface lists
453to release the
454.Vt ifnet
455lock yet keep the
456.Vt ifnet
457structure stable.
458.Pp
459There are in addition a number of function pointers which the driver
460must initialize to complete its interface with the generic interface
461layer:
462.Bl -ohang -offset indent
463.It Fn if_input
464Pass a packet to an appropriate upper layer as determined
465from the link-layer header of the packet.
466This routine is to be called from an interrupt handler or
467used to emulate reception of a packet on this interface.
468A single function implementing
469.Fn if_input
470can be shared among multiple drivers utilizing the same link-layer
471framing, e.g., Ethernet.
472.It Fn if_output
473Output a packet on interface
474.Fa ifp ,
475or queue it on the output queue if the interface is already active.
476.It Fn if_transmit
477Transmit a packet on an interface or queue it if the interface is
478in use.
479This function will return
480.Dv ENOBUFS
481if the devices software and hardware queues are both full.
482This function must be installed after
483.Fn if_attach
484to override the default implementation.
485This function is exposed in order to allow drivers to manage their own queues
486and to reduce the latency caused by a frequently gratuitous enqueue / dequeue
487pair to ifq.
488The suggested internal software queueing mechanism is buf_ring.
489.It Fn if_qflush
490Free mbufs in internally managed queues when the interface is marked down.
491This function must be installed after
492.Fn if_attach
493to override the default implementation.
494This function is exposed in order to allow drivers to manage their own queues
495and to reduce the latency caused by a frequently gratuitous enqueue / dequeue
496pair to ifq.
497The suggested internal software queueing mechanism is buf_ring.
498.It Fn if_start
499Start queued output on an interface.
500This function is exposed in
501order to provide for some interface classes to share a
502.Fn if_output
503among all drivers.
504.Fn if_start
505may only be called when the
506.Dv IFF_DRV_OACTIVE
507flag is not set.
508(Thus,
509.Dv IFF_DRV_OACTIVE
510does not literally mean that output is active, but rather that the
511device's internal output queue is full.) Please note that this function
512will soon be deprecated.
513.It Fn if_ioctl
514Process interface-related
515.Xr ioctl 2
516requests
517(defined in
518.In sys/sockio.h ) .
519Preliminary processing is done by the generic routine
520.Fn ifioctl
521to check for appropriate privileges, locate the interface being
522manipulated, and perform certain generic operations like twiddling
523flags and flushing queues.
524See the description of
525.Fn ifioctl
526below for more information.
527.It Fn if_init
528Initialize and bring up the hardware,
529e.g., reset the chip and enable the receiver unit.
530Should mark the interface running,
531but not active
532.Dv ( IFF_DRV_RUNNING , ~IIF_DRV_OACTIVE ) .
533.It Fn if_resolvemulti
534Check the requested multicast group membership,
535.Fa addr ,
536for validity, and if necessary compute a link-layer group which
537corresponds to that address which is returned in
538.Fa *retsa .
539Returns zero on success, or an error code on failure.
540.El
541.Ss "Interface Flags"
542Interface flags are used for a number of different purposes.
543Some
544flags simply indicate information about the type of interface and its
545capabilities; others are dynamically manipulated to reflect the
546current state of the interface.
547Flags of the former kind are marked
548.Aq S
549in this table; the latter are marked
550.Aq D .
551Flags which begin with
552.Dq IFF_DRV_
553are stored in
554.Va if_drv_flags ;
555all other flags are stored in
556.Va if_flags .
557.Pp
558The macro
559.Dv IFF_CANTCHANGE
560defines the bits which cannot be set by a user program using the
561.Dv SIOCSIFFLAGS
562command to
563.Xr ioctl 2 ;
564these are indicated by an asterisk
565.Pq Ql *
566in the following listing.
567.Pp
568.Bl -tag -width ".Dv IFF_POINTOPOINT" -offset indent -compact
569.It Dv IFF_UP
570.Aq D
571The interface has been configured up by the user-level code.
572.It Dv IFF_BROADCAST
573.Aq S*
574The interface supports broadcast.
575.It Dv IFF_DEBUG
576.Aq D
577Used to enable/disable driver debugging code.
578.It Dv IFF_LOOPBACK
579.Aq S
580The interface is a loopback device.
581.It Dv IFF_POINTOPOINT
582.Aq S*
583The interface is point-to-point;
584.Dq broadcast
585address is actually the address of the other end.
586.It Dv IFF_DRV_RUNNING
587.Aq D*
588The interface has been configured and dynamic resources were
589successfully allocated.
590Probably only useful internal to the
591interface.
592.It Dv IFF_NOARP
593.Aq D
594Disable network address resolution on this interface.
595.It Dv IFF_PROMISC
596.Aq D*
597This interface is in promiscuous mode.
598.It Dv IFF_PPROMISC
599.Aq D
600This interface is in the permanently promiscuous mode (implies
601.Dv IFF_PROMISC ) .
602.It Dv IFF_ALLMULTI
603.Aq D*
604This interface is in all-multicasts mode (used by multicast routers).
605.It Dv IFF_DRV_OACTIVE
606.Aq D*
607The interface's hardware output queue (if any) is full; output packets
608are to be queued.
609.It Dv IFF_SIMPLEX
610.Aq S*
611The interface cannot hear its own transmissions.
612.It Dv IFF_LINK0
613.It Dv IFF_LINK1
614.It Dv IFF_LINK2
615.Aq D
616Control flags for the link layer.
617(Currently abused to select among
618multiple physical layers on some devices.)
619.It Dv IFF_MULTICAST
620.Aq S*
621This interface supports multicast.
622.It Dv IFF_CANTCONFIG
623.Aq S*
624The interface is not configurable in a meaningful way.
625Primarily useful for
626.Dv IFT_USB
627interfaces registered at the interface list.
628.It Dv IFF_MONITOR
629.Aq D
630This interface blocks transmission of packets and discards incoming
631packets after BPF processing.
632Used to monitor network traffic but not interact
633with the network in question.
634.It Dv IFF_STATICARP
635.Aq D
636Used to enable/disable ARP requests on this interface.
637.It Dv IFF_DYING
638.Aq D*
639Set when the
640.Vt ifnet
641structure of this interface is being released and still has
642.Va if_refcount
643references.
644.It Dv IFF_RENAMING
645.Aq D*
646Set when this interface is being renamed.
647.El
648.Ss "Interface Capabilities Flags"
649Interface capabilities are specialized features an interface may
650or may not support.
651These capabilities are very hardware-specific
652and allow, when enabled,
653to offload specific network processing to the interface
654or to offer a particular feature for use by other kernel parts.
655.Pp
656It should be stressed that a capability can be completely
657uncontrolled (i.e., stay always enabled with no way to disable it)
658or allow limited control over itself (e.g., depend on another
659capability's state.)
660Such peculiarities are determined solely by the hardware and driver
661of a particular interface.
662Only the driver possesses
663the knowledge on whether and how the interface capabilities
664can be controlled.
665Consequently, capabilities flags in
666.Va if_capenable
667should never be modified directly by kernel code other than
668the interface driver.
669The command
670.Dv SIOCSIFCAP
671to
672.Fn ifioctl
673is the dedicated means to attempt altering
674.Va if_capenable
675on an interface.
676Userland code shall use
677.Xr ioctl 2 .
678.Pp
679The following capabilities are currently supported by the system:
680.Bl -tag -width ".Dv IFCAP_POLLING_NOCOUNT" -offset indent
681.It Dv IFCAP_RXCSUM
682This interface can do checksum validation on receiving data.
683Some interfaces do not have sufficient buffer storage to store frames
684above a certain MTU-size completely.
685The driver for the interface might disable hardware checksum validation
686if the MTU is set above the hardcoded limit.
687.It Dv IFCAP_TXCSUM
688This interface can do checksum calculation on transmitting data.
689.It Dv IFCAP_HWCSUM
690A shorthand for
691.Pq Dv IFCAP_RXCSUM | IFCAP_TXCSUM .
692.It Dv IFCAP_NETCONS
693This interface can be a network console.
694.It Dv IFCAP_VLAN_MTU
695The
696.Xr vlan 4
697driver can operate over this interface in software tagging mode
698without having to decrease MTU on
699.Xr vlan 4
700interfaces below 1500 bytes.
701This implies the ability of this interface to cope with frames somewhat
702longer than permitted by the Ethernet specification.
703.It Dv IFCAP_VLAN_HWTAGGING
704This interface can do VLAN tagging on output and
705demultiplex frames by their VLAN tag on input.
706.It Dv IFCAP_JUMBO_MTU
707This Ethernet interface can transmit and receive frames up to
7089000 bytes long.
709.It Dv IFCAP_POLLING
710This interface supports
711.Xr polling 4 .
712See below for details.
713.It Dv IFCAP_VLAN_HWCSUM
714This interface can do checksum calculation on both transmitting
715and receiving data on
716.Xr vlan 4
717interfaces (implies
718.Dv IFCAP_HWCSUM ) .
719.It Dv IFCAP_TSO4
720This Ethernet interface supports TCP4 Segmentation offloading.
721.It Dv IFCAP_TSO6
722This Ethernet interface supports TCP6 Segmentation offloading.
723.It Dv IFCAP_TSO
724A shorthand for
725.Pq Dv IFCAP_TSO4 | IFCAP_TSO6 .
726.It Dv IFCAP_TOE4
727This Ethernet interface supports TCP offloading.
728.It Dv IFCAP_TOE6
729This Ethernet interface supports TCP6 offloading.
730.It Dv IFCAP_TOE
731A shorthand for
732.Pq Dv IFCAP_TOE4 | IFCAP_TOE6 .
733.It Dv IFCAP_WOL_UCAST
734This Ethernet interface supports waking up on any Unicast packet.
735.It Dv IFCAP_WOL_MCAST
736This Ethernet interface supports waking up on any Multicast packet.
737.It Dv IFCAP_WOL_MAGIC
738This Ethernet interface supports waking up on any Magic packet such
739as those sent by
740.Xr wake 8 .
741.It Dv IFCAP_WOL
742A shorthand for
743.Pq Dv IFCAP_WOL_UCAST | IFCAP_WOL_MCAST | IFCAP_WOL_MAGIC .
744.It Dv IFCAP_TOE4
745This Ethernet interface supports TCP4 Offload Engine.
746.It Dv IFCAP_TOE6
747This Ethernet interface supports TCP6 Offload Engine.
748.It Dv IFCAP_TOE
749A shorthand for
750.Pq Dv IFCAP_TOE4 | IFCAP_TOE6 .
751.It Dv IFCAP_VLAN_HWFILTER
752This interface supports frame filtering in hardware on
753.Xr vlan 4
754interfaces.
755.It Dv IFCAP_POLLING_NOCOUNT
756The return value for the number of processed packets should be
757skipped for this interface.
758.It Dv IFCAP_VLAN_HWTSO
759This interface supports TCP Segmentation offloading on
760.Xr vlan 4
761interfaces (implies
762.Dv IFCAP_TSO ) .
763.It Dv IFCAP_LINKSTATE
764This Ethernet interface supports dynamic link state changes.
765.El
766.Pp
767The ability of advanced network interfaces to offload certain
768computational tasks from the host CPU to the board is limited
769mostly to TCP/IP.
770Therefore a separate field associated with an interface
771(see
772.Va ifnet.if_data.ifi_hwassist
773below)
774keeps a detailed description of its enabled capabilities
775specific to TCP/IP processing.
776The TCP/IP module consults the field to see which tasks
777can be done on an
778.Em outgoing
779packet by the interface.
780The flags defined for that field are a superset of those for
781.Va mbuf.m_pkthdr.csum_flags ,
782namely:
783.Bl -tag -width ".Dv CSUM_FRAGMENT" -offset indent
784.It Dv CSUM_IP
785The interface will compute IP checksums.
786.It Dv CSUM_TCP
787The interface will compute TCP checksums.
788.It Dv CSUM_UDP
789The interface will compute UDP checksums.
790.It Dv CSUM_IP_FRAGS
791The interface can compute a TCP or UDP checksum for a packet
792fragmented by the host CPU.
793Makes sense only along with
794.Dv CSUM_TCP
795or
796.Dv CSUM_UDP .
797.It Dv CSUM_FRAGMENT
798The interface will do the fragmentation of IP packets if necessary.
799The host CPU does not need to care about MTU on this interface
800as long as a packet to transmit through it is an IP one and it
801does not exceed the size of the hardware buffer.
802.El
803.Pp
804An interface notifies the TCP/IP module about the tasks
805the former has performed on an
806.Em incoming
807packet by setting the corresponding flags in the field
808.Va mbuf.m_pkthdr.csum_flags
809of the
810.Vt mbuf chain
811containing the packet.
812See
813.Xr mbuf 9
814for details.
815.Pp
816The capability of a network interface to operate in
817.Xr polling 4
818mode involves several flags in different
819global variables and per-interface fields.
820The capability flag
821.Dv IFCAP_POLLING
822set in interface's
823.Va if_capabilities
824indicates support for
825.Xr polling 4
826on the particular interface.
827If set in
828.Va if_capabilities ,
829the same flag can be marked or cleared in the interface's
830.Va if_capenable
831within
832.Fn ifioctl ,
833thus initiating switch of the interface to
834.Xr polling 4
835mode or interrupt
836mode, respectively.
837The actual mode change is managed by the driver-specific
838.Fn if_ioctl
839routine.
840The
841.Xr polling
842handler returns the number of packets processed.
843.Ss The Vt if_data Ss Structure
844The
845.Vt if_data
846structure contains statistics and identifying information used
847by management programs, and which is exported to user programs by way
848of the
849.Xr ifmib 4
850branch of the
851.Xr sysctl 3
852MIB.
853The following elements of the
854.Vt if_data
855structure are initialized by the interface and are not expected to change
856significantly over the course of normal operation:
857.Bl -tag -width ".Va ifi_lastchange" -offset indent
858.It Va ifi_type
859.Pq Vt u_char
860The type of the interface, as defined in
861.In net/if_types.h
862and described below in the
863.Sx "Interface Types"
864section.
865.It Va ifi_physical
866.Pq Vt u_char
867Intended to represent a selection of physical layers on devices which
868support more than one; never implemented.
869.It Va ifi_addrlen
870.Pq Vt u_char
871Length of a link-layer address on this device, or zero if there are
872none.
873Used to initialized the address length field in
874.Vt sockaddr_dl
875structures referring to this interface.
876.It Va ifi_hdrlen
877.Pq Vt u_char
878Maximum length of any link-layer header which might be prepended by
879the driver to a packet before transmission.
880The generic code computes
881the maximum over all interfaces and uses that value to influence the
882placement of data in
883.Vt mbuf Ns s
884to attempt to ensure that there is always
885sufficient space to prepend a link-layer header without allocating an
886additional
887.Vt mbuf .
888.It Va ifi_datalen
889.Pq Vt u_char
890Length of the
891.Vt if_data
892structure.
893Allows some stabilization of the routing socket ABI in the face of
894increases in the length of
895.Vt struct ifdata .
896.It Va ifi_mtu
897.Pq Vt u_long
898The maximum transmission unit of the medium, exclusive of any
899link-layer overhead.
900.It Va ifi_metric
901.Pq Vt u_long
902A dimensionless metric interpreted by a user-mode routing process.
903.It Va ifi_baudrate
904.Pq Vt u_long
905The line rate of the interface, in bits per second.
906.It Va ifi_hwassist
907.Pq Vt u_long
908A detailed interpretation of the capabilities
909to offload computational tasks for
910.Em outgoing
911packets.
912The interface driver must keep this field in accord with
913the current value of
914.Va if_capenable .
915.It Va ifi_epoch
916.Pq Vt time_t
917The system uptime when interface was attached or the statistics
918below were reset.
919This is intended to be used to set the SNMP variable
920.Va ifCounterDiscontinuityTime .
921It may also be used to determine if two successive queries for an
922interface of the same index have returned results for the same
923interface.
924.El
925.Pp
926The structure additionally contains generic statistics applicable to a
927variety of different interface types (except as noted, all members are
928of type
929.Vt u_long ) :
930.Bl -tag -width ".Va ifi_lastchange" -offset indent
931.It Va ifi_link_state
932.Pq Vt u_char
933The current link state of Ethernet interfaces.
934See the
935.Sx Interface Link States
936section for possible values.
937.It Va ifi_ipackets
938Number of packets received.
939.It Va ifi_ierrors
940Number of receive errors detected (e.g., FCS errors, DMA overruns,
941etc.).
942More detailed breakdowns can often be had by way of a
943link-specific MIB.
944.It Va ifi_opackets
945Number of packets transmitted.
946.It Va ifi_oerrors
947Number of output errors detected (e.g., late collisions, DMA overruns,
948etc.).
949More detailed breakdowns can often be had by way of a
950link-specific MIB.
951.It Va ifi_collisions
952Total number of collisions detected on output for CSMA interfaces.
953(This member is sometimes [ab]used by other types of interfaces for
954other output error counts.)
955.It Va ifi_ibytes
956Total traffic received, in bytes.
957.It Va ifi_obytes
958Total traffic transmitted, in bytes.
959.It Va ifi_imcasts
960Number of packets received which were sent by link-layer multicast.
961.It Va ifi_omcasts
962Number of packets sent by link-layer multicast.
963.It Va ifi_iqdrops
964Number of packets dropped on input.
965Rarely implemented.
966.It Va ifi_noproto
967Number of packets received for unknown network-layer protocol.
968.It Va ifi_lastchange
969.Pq Vt "struct timeval"
970The time of the last administrative change to the interface (as required
971for
972.Tn SNMP ) .
973.El
974.Ss Interface Types
975The header file
976.In net/if_types.h
977defines symbolic constants for a number of different types of
978interfaces.
979The most common are:
980.Pp
981.Bl -tag -offset indent -width ".Dv IFT_PROPVIRTUAL" -compact
982.It Dv IFT_OTHER
983none of the following
984.It Dv IFT_ETHER
985Ethernet
986.It Dv IFT_ISO88023
987ISO 8802-3 CSMA/CD
988.It Dv IFT_ISO88024
989ISO 8802-4 Token Bus
990.It Dv IFT_ISO88025
991ISO 8802-5 Token Ring
992.It Dv IFT_ISO88026
993ISO 8802-6 DQDB MAN
994.It Dv IFT_FDDI
995FDDI
996.It Dv IFT_PPP
997Internet Point-to-Point Protocol
998.Pq Xr ppp 8
999.It Dv IFT_LOOP
1000The loopback
1001.Pq Xr lo 4
1002interface
1003.It Dv IFT_SLIP
1004Serial Line IP
1005.It Dv IFT_PARA
1006Parallel-port IP
1007.Pq Dq Tn PLIP
1008.It Dv IFT_ATM
1009Asynchronous Transfer Mode
1010.It Dv IFT_USB
1011USB Interface
1012.El
1013.Ss Interface Link States
1014The following link states are currently defined:
1015.Pp
1016.Bl -tag -offset indent -width ".Dv LINK_STATE_UNKNOWN" -compact
1017.It Dv LINK_STATE_UNKNOWN
1018The link is in an invalid or unknown state.
1019.It Dv LINK_STATE_DOWN
1020The link is down.
1021.It Dv LINK_STATE_UP
1022The link is up.
1023.El
1024.Ss The Vt ifaddr Ss Structure
1025Every interface is associated with a list
1026(or, rather, a
1027.Li TAILQ )
1028of addresses, rooted at the interface structure's
1029.Va if_addrlist
1030member.
1031The first element in this list is always an
1032.Dv AF_LINK
1033address representing the interface itself; multi-access network
1034drivers should complete this structure by filling in their link-layer
1035addresses after calling
1036.Fn if_attach .
1037Other members of the structure represent network-layer addresses which
1038have been configured by means of the
1039.Dv SIOCAIFADDR
1040command to
1041.Xr ioctl 2 ,
1042called on a socket of the appropriate protocol family.
1043The elements of this list consist of
1044.Vt ifaddr
1045structures.
1046Most protocols will declare their own protocol-specific
1047interface address structures, but all begin with a
1048.Vt "struct ifaddr"
1049which provides the most-commonly-needed functionality across all
1050protocols.
1051Interface addresses are reference-counted.
1052.Pp
1053The members of
1054.Vt "struct ifaddr"
1055are as follows:
1056.Bl -tag -width ".Va ifa_rtrequest" -offset indent
1057.It Va ifa_addr
1058.Pq Vt "struct sockaddr *"
1059The local address of the interface.
1060.It Va ifa_dstaddr
1061.Pq Vt "struct sockaddr *"
1062The remote address of point-to-point interfaces, and the broadcast
1063address of broadcast interfaces.
1064.Va ( ifa_broadaddr
1065is a macro for
1066.Va ifa_dstaddr . )
1067.It Va ifa_netmask
1068.Pq Vt "struct sockaddr *"
1069The network mask for multi-access interfaces, and the confusion
1070generator for point-to-point interfaces.
1071.It Va ifa_ifp
1072.Pq Vt "struct ifnet *"
1073A link back to the interface structure.
1074.It Va ifa_link
1075.Pq Fn TAILQ_ENTRY ifaddr
1076.Xr queue 3
1077glue for list of addresses on each interface.
1078.It Va ifa_rtrequest
1079See below.
1080.It Va ifa_flags
1081.Pq Vt u_short
1082Some of the flags which would be used for a route representing this
1083address in the route table.
1084.It Va ifa_refcnt
1085.Pq Vt short
1086The reference count.
1087.It Va ifa_metric
1088.Pq Vt int
1089A metric associated with this interface address, for the use of some
1090external routing protocol.
1091.El
1092.Pp
1093References to
1094.Vt ifaddr
1095structures are gained by calling the
1096.Fn ifa_ref
1097function and released by calling the
1098.Fn ifa_free
1099function.
1100.Pp
1101.Fn ifa_rtrequest
1102is a pointer to a function which receives callouts from the routing
1103code
1104.Pq Fn rtrequest
1105to perform link-layer-specific actions upon requests to add,
1106or delete routes.
1107The
1108.Fa cmd
1109argument indicates the request in question:
1110.Dv RTM_ADD ,
1111or
1112.Dv RTM_DELETE .
1113The
1114.Fa rt
1115argument is the route in question; the
1116.Fa info
1117argument contains the specific destination being manipulated.
1118.Sh FUNCTIONS
1119The functions provided by the generic interface code can be divided
1120into two groups: those which manipulate interfaces, and those which
1121manipulate interface addresses.
1122In addition to these functions, there
1123may also be link-layer support routines which are used by a number of
1124drivers implementing a specific link layer over different hardware;
1125see the documentation for that link layer for more details.
1126.Ss The Vt ifmultiaddr Ss Structure
1127Every multicast-capable interface is associated with a list of
1128multicast group memberships, which indicate at a low level which
1129link-layer multicast addresses (if any) should be accepted, and at a
1130high level, in which network-layer multicast groups a user process has
1131expressed interest.
1132.Pp
1133The elements of the structure are as follows:
1134.Bl -tag -width ".Va ifma_refcount" -offset indent
1135.It Va ifma_link
1136.Pq Fn LIST_ENTRY ifmultiaddr
1137.Xr queue 3
1138macro glue.
1139.It Va ifma_addr
1140.Pq Vt "struct sockaddr *"
1141A pointer to the address which this record represents.
1142The
1143memberships for various address families are stored in arbitrary
1144order.
1145.It Va ifma_lladdr
1146.Pq Vt "struct sockaddr *"
1147A pointer to the link-layer multicast address, if any, to which the
1148network-layer multicast address in
1149.Va ifma_addr
1150is mapped, else a null pointer.
1151If this element is non-nil, this
1152membership also holds an invisible reference to another membership for
1153that link-layer address.
1154.It Va ifma_refcount
1155.Pq Vt u_int
1156A reference count of requests for this particular membership.
1157.El
1158.Ss Interface Manipulation Functions
1159.Bl -ohang -offset indent
1160.It Fn if_alloc
1161Allocate and initialize
1162.Vt "struct ifnet" .
1163Initialization includes the allocation of an interface index and may
1164include the allocation of a
1165.Fa type
1166specific structure in
1167.Va if_l2com .
1168.It Fn if_attach
1169Link the specified interface
1170.Fa ifp
1171into the list of network interfaces.
1172Also initialize the list of
1173addresses on that interface, and create a link-layer
1174.Vt ifaddr
1175structure to be the first element in that list.
1176(A pointer to
1177this address structure is saved in the
1178.Vt ifnet
1179structure and shall be accessed by the
1180.Fn ifaddr_byindex
1181function.)
1182The
1183.Fa ifp
1184must have been allocated by
1185.Fn if_alloc .
1186.It Fn if_detach
1187Shut down and unlink the specified
1188.Fa ifp
1189from the interface list.
1190.It Fn if_free
1191Free the given
1192.Fa ifp
1193back to the system.
1194The interface must have been previously detached if it was ever attached.
1195.It Fn if_free_type
1196Identical to
1197.Fn if_free
1198except that the given
1199.Fa type
1200is used to free
1201.Va if_l2com
1202instead of the type in
1203.Va if_type .
1204This is intended for use with drivers that change their interface type.
1205.It Fn if_down
1206Mark the interface
1207.Fa ifp
1208as down (i.e.,
1209.Dv IFF_UP
1210is not set),
1211flush its output queue, notify protocols of the transition,
1212and generate a message from the
1213.Xr route 4
1214routing socket.
1215.It Fn if_up
1216Mark the interface
1217.Fa ifp
1218as up, notify protocols of the transition,
1219and generate a message from the
1220.Xr route 4
1221routing socket.
1222.It Fn ifpromisc
1223Add or remove a promiscuous reference to
1224.Fa ifp .
1225If
1226.Fa pswitch
1227is true, add a reference;
1228if it is false, remove a reference.
1229On reference count transitions
1230from zero to one and one to zero, set the
1231.Dv IFF_PROMISC
1232flag appropriately and call
1233.Fn if_ioctl
1234to set up the interface in the desired mode.
1235.It Fn if_allmulti
1236As
1237.Fn ifpromisc ,
1238but for the all-multicasts
1239.Pq Dv IFF_ALLMULTI
1240flag instead of the promiscuous flag.
1241.It Fn ifunit
1242Return an
1243.Vt ifnet
1244pointer for the interface named
1245.Fa name .
1246.It Fn ifunit_ref
1247Return a reference-counted (via
1248.Fn ifa_ref )
1249.Vt ifnet
1250pointer for the interface named
1251.Fa name .
1252This is the preferred function over
1253.Fn ifunit .
1254The caller is responsible for releasing the reference with
1255.Fn if_rele
1256when it is finished with the ifnet.
1257.It Fn ifioctl
1258Process the ioctl request
1259.Fa cmd ,
1260issued on socket
1261.Fa so
1262by thread
1263.Fa td ,
1264with data parameter
1265.Fa data .
1266This is the main routine for handling all interface configuration
1267requests from user mode.
1268It is ordinarily only called from the socket-layer
1269.Xr ioctl 2
1270handler, and only for commands with class
1271.Sq Li i .
1272Any unrecognized commands will be passed down to socket
1273.Fa so Ns 's
1274protocol for
1275further interpretation.
1276The following commands are handled by
1277.Fn ifioctl :
1278.Pp
1279.Bl -tag -width ".Dv SIOCGIFNETMASK" -offset indent -compact
1280.It Dv SIOCGIFCONF
1281Get interface configuration.
1282(No call-down to driver.)
1283.Pp
1284.It Dv SIOCSIFNAME
1285Set the interface name.
1286.Dv RTM_IFANNOUNCE
1287departure and arrival messages are sent so that
1288routing code that relies on the interface name will update its interface
1289list.
1290Caller must have appropriate privilege.
1291(No call-down to driver.)
1292.It Dv SIOCGIFCAP
1293.It Dv SIOCGIFFIB
1294.It Dv SIOCGIFFLAGS
1295.It Dv SIOCGIFMETRIC
1296.It Dv SIOCGIFMTU
1297.It Dv SIOCGIFPHYS
1298Get interface capabilities, FIB, flags, metric, MTU, medium selection.
1299(No call-down to driver.)
1300.Pp
1301.It Dv SIOCSIFCAP
1302Enable or disable interface capabilities.
1303Caller must have appropriate privilege.
1304Before a call to the driver-specific
1305.Fn if_ioctl
1306routine, the requested mask for enabled capabilities is checked
1307against the mask of capabilities supported by the interface,
1308.Va if_capabilities .
1309Requesting to enable an unsupported capability is invalid.
1310The rest is supposed to be done by the driver,
1311which includes updating
1312.Va if_capenable
1313and
1314.Va if_data.ifi_hwassist
1315appropriately.
1316.Pp
1317.It Dv SIOCSIFFIB
1318Sets interface FIB.
1319Caller must have appropriate privilege.
1320FIB values start at 0 and values greater or equals than
1321.Va net.fibs
1322are considered invalid.
1323.It Dv SIOCSIFFLAGS
1324Change interface flags.
1325Caller must have appropriate privilege.
1326If a change to the
1327.Dv IFF_UP
1328flag is requested,
1329.Fn if_up
1330or
1331.Fn if_down
1332is called as appropriate.
1333Flags listed in
1334.Dv IFF_CANTCHANGE
1335are masked off, and the field
1336.Va if_flags
1337in the interface structure is updated.
1338Finally, the driver
1339.Fn if_ioctl
1340routine is called to perform any setup
1341requested.
1342.Pp
1343.It Dv SIOCSIFMETRIC
1344.It Dv SIOCSIFPHYS
1345Change interface metric or medium.
1346Caller must have appropriate privilege.
1347.Pp
1348.It Dv SIOCSIFMTU
1349Change interface MTU.
1350Caller must have appropriate privilege.
1351MTU
1352values less than 72 or greater than 65535 are considered invalid.
1353The driver
1354.Fn if_ioctl
1355routine is called to implement the change; it is responsible for any
1356additional sanity checking and for actually modifying the MTU in the
1357interface structure.
1358.Pp
1359.It Dv SIOCADDMULTI
1360.It Dv SIOCDELMULTI
1361Add or delete permanent multicast group memberships on the interface.
1362Caller must have appropriate privilege.
1363The
1364.Fn if_addmulti
1365or
1366.Fn if_delmulti
1367function is called to perform the operation; qq.v.
1368.Pp
1369.It Dv SIOCAIFADDR
1370.It Dv SIOCDIFADDR
1371The socket's protocol control routine is called to implement the
1372requested action.
1373.Pp
1374.El
1375.El
1376.Pp
1377.Fn if_down ,
1378.Fn ifioctl ,
1379.Fn ifpromisc ,
1380and
1381.Fn if_up
1382must be called at
1383.Fn splnet
1384or higher.
1385.Ss "Interface Address Functions"
1386Several functions exist to look up an interface address structure
1387given an address.
1388.Fn ifa_ifwithaddr
1389returns an interface address with either a local address or a
1390broadcast address precisely matching the parameter
1391.Fa addr .
1392.Fn ifa_ifwithdstaddr
1393returns an interface address for a point-to-point interface whose
1394remote
1395.Pq Dq destination
1396address is
1397.Fa addr .
1398.Pp
1399.Fn ifa_ifwithnet
1400returns the most specific interface address which matches the
1401specified address,
1402.Fa addr ,
1403subject to its configured netmask, or a point-to-point interface
1404address whose remote address is
1405.Fa addr
1406if one is found.
1407If
1408.Fa ignore_ptp
1409is true, skip point-to-point interface addresses.
1410.Pp
1411.Fn ifaof_ifpforaddr
1412returns the most specific address configured on interface
1413.Fa ifp
1414which matches address
1415.Fa addr ,
1416subject to its configured netmask.
1417If the interface is
1418point-to-point, only an interface address whose remote address is
1419precisely
1420.Fa addr
1421will be returned.
1422.Pp
1423.Fn ifaddr_byindex
1424returns the link-level address of the interface with the given index
1425.Fa idx .
1426.Pp
1427All of these functions return a null pointer if no such address can be
1428found.
1429.Ss "Interface Multicast Address Functions"
1430The
1431.Fn if_addmulti ,
1432.Fn if_delmulti ,
1433and
1434.Fn if_findmulti
1435functions provide support for requesting and relinquishing multicast
1436group memberships, and for querying an interface's membership list,
1437respectively.
1438The
1439.Fn if_addmulti
1440function takes a pointer to an interface,
1441.Fa ifp ,
1442and a generic address,
1443.Fa sa .
1444It also takes a pointer to a
1445.Vt "struct ifmultiaddr *"
1446which is filled in on successful return with the address of the
1447group membership control block.
1448The
1449.Fn if_addmulti
1450function performs the following four-step process:
1451.Bl -enum -offset indent
1452.It
1453Call the interface's
1454.Fn if_resolvemulti
1455entry point to determine the link-layer address, if any, corresponding
1456to this membership request, and also to give the link layer an
1457opportunity to veto this membership request should it so desire.
1458.It
1459Check the interface's group membership list for a pre-existing
1460membership for this group.
1461If one is not found, allocate a new one;
1462if one is, increment its reference count.
1463.It
1464If the
1465.Fn if_resolvemulti
1466routine returned a link-layer address corresponding to the group,
1467repeat the previous step for that address as well.
1468.It
1469If the interface's multicast address filter needs to be changed
1470because a new membership was added, call the interface's
1471.Fn if_ioctl
1472routine
1473(with a
1474.Fa cmd
1475argument of
1476.Dv SIOCADDMULTI )
1477to request that it do so.
1478.El
1479.Pp
1480The
1481.Fn if_delmulti
1482function, given an interface
1483.Fa ifp
1484and an address,
1485.Fa sa ,
1486reverses this process.
1487Both functions return zero on success, or a
1488standard error number on failure.
1489.Pp
1490The
1491.Fn if_findmulti
1492function examines the membership list of interface
1493.Fa ifp
1494for an address matching
1495.Fa sa ,
1496and returns a pointer to that
1497.Vt "struct ifmultiaddr"
1498if one is found, else it returns a null pointer.
1499.Sh SEE ALSO
1500.Xr ioctl 2 ,
1501.Xr link_addr 3 ,
1502.Xr queue 3 ,
1503.Xr sysctl 3 ,
1504.Xr bpf 4 ,
1505.Xr ifmib 4 ,
1506.Xr lo 4 ,
1507.Xr netintro 4 ,
1508.Xr polling 4 ,
1509.Xr config 8 ,
1510.Xr ppp 8 ,
1511.Xr mbuf 9 ,
1512.Xr rtentry 9
1513.Rs
1514.%A Gary R. Wright
1515.%A W. Richard Stevens
1516.%B TCP/IP Illustrated
1517.%V Vol. 2
1518.%O Addison-Wesley, ISBN 0-201-63354-X
1519.Re
1520.Sh AUTHORS
1521This manual page was written by
1522.An Garrett A. Wollman .
1523