ifnet(9)

NAME

ifnet, ifaddr, ifqueue, if_data - kernel interfaces for ma
nipulating network interfaces

SYNOPSIS

#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);
void
if_attach(struct ifnet *ifp);
void
if_detach(struct ifnet *ifp);
void
if_free(struct ifnet *ifp);
void
if_free_type(struct ifnet *ifp, u_char type);
void
if_down(struct ifnet *ifp);
int
ifioctl(struct  socket *so, u_long cmd, caddr_t data, struct
thread *td);
int
ifpromisc(struct ifnet *ifp, int pswitch);
int
if_allmulti(struct ifnet *ifp, int amswitch);
struct ifnet *
ifunit(const char *name);
void
if_up(struct ifnet *ifp);
Interface Address Functions
struct ifaddr *
ifa_ifwithaddr(struct sockaddr *addr);
struct ifaddr *
ifa_ifwithdstaddr(struct sockaddr *addr);
struct ifaddr *
ifa_ifwithnet(struct sockaddr *addr);
struct ifaddr *
ifaof_ifpforaddr(struct sockaddr *addr, struct ifnet *ifp);
void
ifafree(struct ifaddr *ifa);
IFAFREE(struct ifaddr *ifa);
Interface Multicast Address Functions
int
if_addmulti(struct ifnet *ifp, struct sockaddr *sa,
        struct ifmultiaddr **ifmap);
int
if_delmulti(struct ifnet *ifp, struct sockaddr *sa);
struct ifmultiaddr *
ifmaof_ifpforaddr(struct sockaddr *addr, struct ifnet *ifp);
Output queue macros
IF_DEQUEUE(struct ifqueue *ifq, struct mbuf *m);
struct ifnet Member Functions
void
(*if_input)(struct ifnet *ifp, struct mbuf *m);
int
(*if_output)(struct  ifnet  *ifp,  struct  mbuf  *m,  struct
sockaddr *dst,
        struct rtentry *rt);
void
(*if_start)(struct ifnet *ifp);
int
(*if_done)(struct ifnet *ifp);
int
(*if_ioctl)(struct ifnet *ifp, int cmd, caddr_t data);
void
(*if_watchdog)(struct ifnet *ifp);
int
(*if_poll_recv)(struct ifnet *ifp, int *quotap);
int
(*if_poll_xmit)(struct ifnet *ifp, int *quotap);
void
(*if_poll_inttrn)(struct ifnet *ifp);
void
(*if_poll_slowinput)(struct ifnet *ifp, struct mbuf *m);
void
(*if_init)(void *if_softc);
int
(*if_resolvemulti)(struct  ifnet   *ifp,   struct   sockaddr
**retsa,
        struct sockaddr *addr);
struct ifaddr member function
void
(*ifa_rtrequest)(int   cmd,   struct   rtentry  *rt,  struct
sockaddr *dst);
Global Variables
extern struct ifnethead ifnet;
extern struct ifaddr **ifnet_addrs;
extern int if_index;
extern int ifqmaxlen;

DATA STRUCTURES

The kernel mechanisms for handling network interfaces reside
primarily in
the ifnet, if_data, ifaddr, and ifmultiaddr structures in
#include
<net/if.h>
and #include <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 de
fined in 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 #include
<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 #include <net/if_var.h> because it is the prerequisite of some other header file
like Most references to those two files in particular can be replaced by
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 kernel routines which manipulate interface as such accept or
return pointers to these structures. Each interface structure contains an
if_data structure, which 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. Each interface also
has a TAILQ of interface addresses, described by ifaddr structures; the
head of the queue is always an AF_LINK address (see link_addr(3)) de
scribing the link layer implemented by the interface (if any). (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 driv

er'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_alloc().)
if_link (TAILQ_ENTRY(ifnet)) queue(3)
macro glue.
if_xname (char *) The name of the inter
face, (e.g.,: ``fxp0'' or ``lo0''). (Initial; ized by
driver.)
if_dname (const char *) The name of the
driver. (Ini: tialized by driver.)
if_dunit (int) A unique number assigned to
each inter: face managed by a particular; driver. Drivers
may choose to set this to; IF_DUNIT_NONE if a
unit number is not associated; with the device.
(Initialized by driver.)
if_addrhead (struct ifaddrhead) The head of
the queue(3): TAILQ containing the list of ad; dresses
assigned to this interface.
if_pcount (int) A count of promiscuous lis
teners on this: interface, used to reference; count the
IFF_PROMISC flag.
if_bpf (struct bpf_if *) Opaque per-in
terface data: for the packet filter, bpf(4).; (Initialized
by bpf_attach().)
if_index (u_short) A unique number as
signed to each: interface 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_timer (short) Number of seconds until
the watchdog: timer if_watchdog() is called, or; zero if the
timer is disabled. (Set by driv; er, decremented by generic watchdog code.)
if_flags (int) Flags describing opera
tional parameters: of this interface (see below).; (Manipulated
by both driver and generic code.)
if_capabilities (int) Flags describing the capa
bilities the: interface supports (see below).
if_capenable (int) Flags describing the en
abled capabili: ties of the interface (see be; low).
if_linkmib (void *) A pointer to an inter
face-specific: MIB structure exported by; ifmib(4). (Initialized by driver.)
if_linkmiblen (size_t) The size of said struc
ture. (Ini: tialized by driver.)
if_data (struct if_data) More statistics
and informa: tion; see The if_data structure,; below. (Initialized by driver, manipulated; by both driver
and generic code.)
if_snd (struct ifqueue) The output
queue. (Manipu: lated by driver.)
There are in addition a number of function pointers which
the driver must initialize to complete its interface with the generic inter
face layer:: if_input()
Pass a packet to an appropriate upper layer as deter; mined 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 framing, e.g., Ethernet.; if_output()
Output a packet on interface ifp, or queue it on the; output queue
if the interface is already active.; if_start()
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_OACTIVE flag is not set. (Thus, IFF_OACTIVE does; not literally
mean that output is active, but rather that the de; vice's internal
output queue is full.); if_done()
Not used. We are not even sure what it was ever for.; The prototype is faked.; if_ioctl()
Process interface-related ioctl(2) requests (defined; in Preliminary
processing is done by the generic routine ifioctl() to; check for
appropriate privileges, locate the interface being ma; nipulated, and
perform certain generic operations like twiddling; flags and flushing queues. See the description of ifioctl() below; for more information.; if_watchdog()
Routine called by the generic code when the watchdog; timer,
if_timer, expires. Usually this will reset the inter; face.; if_init()
Initialize and bring up the hardware, e.g., reset the; chip and the
watchdog timer and enable the receiver unit. Should; mark the
interface running, but not active (IFF_RUNNING,; ~IIF_OACTIVE).; if_resolvemulti()
Check the requested multicast group membership, addr,; for validity,
and if necessary compute a link-layer group which cor; responds to
that address which is returned in *retsa. Returns ze; ro 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 capabilities; others are dynamically manipulated to reflect the cur; rent state of
the interface. Flags of the former kind are marked <S> in; this table;
the latter are marked <D>.; 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 con

figured 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_RUNNING <D*> The interface has been con

figured and

dynamic resources were success

fully allocated.
Probably only useful internal to

the interface.

IFF_NOARP <D> Disable network address reso

lution on this

interface.

IFF_PROMISC <D*> This interface is in promis

cuous mode.
IFF_PPROMISC <D> This interface is in the per

manently

promiscuous mode (implies

IFF_PROMISC).

IFF_ALLMULTI <D*> This interface is in all

multicasts mode

(used by multicast routers).

IFF_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 trans

missions.

IFF_LINK0
IFF_LINK1
IFF_LINK2 <D> Control flags for the link

layer. (Cur

rently abused to select among

multiple physical layers on some devices.)

IFF_MULTICAST <S*> This interface supports mul

ticast.
IFF_POLLING <D*> The interface is in

polling(4) mode. See

Interface Capabilities Flags for

details.
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 al; low limited
control over itself (e.g., depend on another capability's; state.) Such
peculiarities are determined solely by the hardware and; driver of a particular interface. Only the driver possesses the knowledge; on whether
and how the interface capabilities can be controlled. Con; sequently,
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_NETCONS This interface can be a net

work console.

IFCAP_POLLING This interface supports

polling(4). See
below for details.
IFCAP_RXCSUM This interface can do check
sum validation: on receiving data. Some in; terfaces do
not have sufficient buffer; storage to
store frames above a certain; MTU-size
completely. The driver for; the interface
might disable hardware; checksum validation if the MTU is set above; the hardcoded limit.
IFCAP_TXCSUM This interface can do check
sum calcula: tion on transmitting data.
IFCAP_HWCSUM A shorthand for (IFCAP_RXC
SUM: IFCAP_TXCSUM).
IFCAP_VLAN_HWTAGGING This interface can do VLAN
tagging on: output and demultiplex; frames by their
VLAN tag on input.
IFCAP_VLAN_MTU The vlan(4) driver can oper
ate over this: interface in software tag; ging mode without having to decrease MTU; on vlan(4)
interfaces below 1500 bytes.; This
implies the ability of this; interface to
cope with frames somewhat; longer than
permitted by the Ethernet; specification.
IFCAP_JUMBO_MTU This Ethernet interface can
transmit and: receive frames up to 9000; bytes long.
The ability of advanced network interfaces to offload cer
tain computational tasks from the host CPU to the board is limited most
ly to TCP/IP.
Therefore a separate field associated with an interface (see
ifnet.if_data.ifi_hwassist below) keeps a detailed descrip
tion 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.; CSUM_IP_FRAGS The interface can compute a TCP or; UDP checksum
for a packet fragmented by the host

CPU. Makes
sense only along with CSUM_TCP or

CSUM_UDP.
CSUM_FRAGMENT The interface will do the fragmen
tation of IP: packets if necessary. The host CPU; does not
need to care about MTU on this in; terface as long
as a packet to transmit through it; is an IP one
and it does not exceed the size of; the hardware
buffer.
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. First, there is a system-wide sysctl(8) master
switch named kern.polling.enable, which can toggle polling(4) globally.
If that variable is set to non-zero, polling(4) will be used on those
devices where it is enabled individually. Otherwise, polling(4) will not
be used in the system. Second, the capability flag IFCAP_POLLING set
in interface's
if_capabilities indicates support for polling(4) on the par
ticular interface. If set in if_capabilities, the same flag can be
marked or cleared
in the interface's if_capenable, thus initiating switch of
the interface to polling(4) mode or interrupt mode, respectively. The ac
tual mode change will occur at an implementation-specific moment in
the future, e.g., during the next interrupt or polling(4) cycle. And
finally, if the mode transition has been successful, the flag IFF_POLLING is
marked or
cleared in the interface's if_flags to indicate the current
mode of the interface.
The if_data Structure: In 4.4BSD, a subset of the interface information believed to; be of interest to management stations was segregated from the ifnet; structure and
moved into its own if_data structure to facilitate its use; by user programs. The following elements of the if_data structure are; initialized
by the interface and are not expected to change significant; ly over the
course of normal operation:

ifi_type (u_char) The type of the inter

face, as defined
in #include <net/if_types.h> and described below in the

Interface Types section.
ifi_physical (u_char) Intended to represent a
selection of: physical 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
initialized 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 en; sure that
there is always sufficient space; to prepend a
link-layer header without allocat; ing 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-lay; er overhead.
ifi_metric (u_long) A dimensionless metric
interpreted by: a user-mode routing process.
ifi_baudrate (u_long) The line rate of the in
terface, in: bits per second.
ifi_hwassist (u_long) A detailed interpretation
of the capa: bilities 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 interface of the; same index have
returned results for the same in; terface.
The structure additionally contains generic statistics ap
plicable 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
interfaces. 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
breakdowns can often be had by way; of a linkspecific MIB.
ifi_opackets Number of packets transmitted.
ifi_oerrors Number of output errors detected
(e.g., late: collisions, DMA overruns, etc.).; More detailed
breakdowns can often be had by way; of a linkspecific MIB.
ifi_collisions Total number of collisions detect
ed on output: for CSMA interfaces. (This member; is sometimes
[ab]used by other types of inter; faces 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 in
put. Rarely: implemented.
ifi_noproto Number of packets received for un
known network: layer protocol.
ifi_lastchange (struct timeval) The time of the
last adminis: trative change to the interface; (as required
for SNMP).
Interface Types: The header file #include <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_FDDI FDDI
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
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_addrlist; member. The
first element in this list is always an AF_LINK address rep; resenting the
interface itself; multi-access network drivers should com; plete this
structure by filling in their link-layer addresses after; calling
if_attach(). Other members of the structure represent net; work-layer
addresses which have been configured by means of the SIO; CAIFADDR 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 struc; tures, but all
begin with a struct ifaddr which provides the most-commonly; needed functionality across all protocols. Interface addresses are; referencecounted.; The members of struct ifaddr are as follows:

ifa_addr (struct sockaddr *) The local ad

dress of the
interface.
ifa_dstaddr (struct sockaddr *) The remote ad
dress of point: to-point interfaces, and the broad; cast address
of broadcast interfaces.; (ifa_broadaddr is a
macro for ifa_dstaddr.)
ifa_netmask (struct sockaddr *) The network
mask for multi: access interfaces, and the confu; sion generator
for point-to-point interfaces.
ifa_ifp (struct ifnet *) A link back to the
interface: structure.
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 ad; dress in the
route table.
ifa_refcnt (short) The reference count.
ifa_metric (int) A metric associated with this
interface: address, for the use of some exter; nal routing
protocol.
References to ifaddr structures are gained manually, by in
crementing the
ifa_refcnt member. References are released by calling ei
ther the
ifafree() function or the IFAFREE() macro.
ifa_rtrequest() is a pointer to a function which receives
callouts from
the routing code (rtrequest()) to perform link-layer-specif
ic actions upon requests to add, resolve, or delete routes. The cmd
argument indicates the request in question: RTM_ADD, RTM_RESOLVE, or
RTM_DELETE. The rt argument is the route in question; the dst argument is
the specific destination being manipulated for RTM_RESOLVE, or a null
pointer otherwise.

FUNCTIONS

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 implementing a specific link layer over different hardware; see
the documentation 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 multicast 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: multicast address, if any, to which; the networklayer multicast address in; ifma_addr is mapped,
else a null pointer. If this ele; ment is nonnil, this membership also holds an; invisible
reference to another membership for; that linklayer address.
ifma_refcount (u_int) A reference count of re
quests for this: particular membership.
Interface Manipulation Functions: if_alloc()
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.; if_attach()
Link the specified interface ifp into the list of net; work interfaces. 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
global array ifnet_addrs.) The ifp must have been al; locted by
if_alloc().; if_detach()
Shut down and unlink the specified ifp from the inter; face list.; if_free()
Free the given ifp back to the system. The interface; must have
been previously detached if it was ever attached.; if_free_type()
Identical to if_free() except that the given type is; used to free
if_l2com instead of the type in if_type. This is in; tended for use
with drivers that change their interface type.; if_down()
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.; if_up()
Mark the interface ifp as up, notify protocols of the; transition,
and generate a message from the route(4) routing sock; et.; ifpromisc()
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.; if_allmulti()
As ifpromisc(), but for the all-multicasts (IFF_ALL; MULTI) flag
instead of the promiscuous flag.; ifunit()
Return an ifnet pointer for the interface named name.; ifioctl()
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 ordinarily only called from the socket-layer ioctl(2) han; dler, and only
for commands with class `i'. Any unrecognized com; mands will be
passed down to socket so's protocol for further inter; pretation.
The following commands are handled by ifioctl():

SIOCGIFCONF
OSIOCGIFCONF Get interface configura

tion. (No call
down to driver.)
SIOCSIFNAME Set the interface name.
RTM_IFANNOUNCE: departure and arrival mes; sages are sent
so that routing code that; relies on the
interface name will update; its interface
list. Caller must have ap; propriate
privilege. (No call-down; to driver.)
SIOCGIFCAP SIOCGIFFLAGS SIOCGIFMETRIC SIOCGIFMTU SIOCGIFPHYS Get interface capabilities,
flags, met: ric, MTU, medium selection.; (No calldown to driver.)
SIOCSIFCAP Enable or disable interface
capabili: ties. Caller must have ap; propriate
privilege. Before a call; to the driverspecific if_ioctl() rou; tine, the
requested mask for enabled; capabilities
is checked against the mask; of capabilities supported by the in; terface,
if_capabilities. Request; ing to enable
an unsupported capability; is invalid.
The rest is supposed to be; done by the
driver, which includes up; dating
if_capenable and; if_data.ifi_hwassist
appropriately.
SIOCSIFFLAGS Change interface flags.
Caller must: have appropriate privilege.; If a change
to the IFF_UP flag is re; quested, 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
requested.
SIOCSIFMETRIC SIOCSIFPHYS Change interface metric or
medium.: Caller must have appropri; ate privilege.
SIOCSIFMTU Change interface MTU.
Caller must have: appropriate privilege. MTU; values less
than 72 or greater than; 65535 are considered invalid. The driv; er if_ioctl()
routine is called to imple; ment the
change; it is responsible; for any additional sanity checking and; for actually
modifying the MTU in the; interface
structure.
SIOCADDMULTI SIOCDELMULTI Add or delete permanent
multicast group: memberships on the inter; face. Caller
must have appropriate priv; ilege. The
if_addmulti() or; if_delmulti() function
is called to perform the; operation;
qq.v.
SIOCSIFDSTADDR SIOCSIFADDR SIOCSIFBRDADDR SIOCSIFNETMASK The socket's protocol con
trol routine is: called to implement the re; quested
action.
OSIOGIFADDR OSIOCGIFDSTADDR OSIOCGIFBRDADDR OSIOCGIFNETMASK The socket's protocol con
trol routine is: called to implement the re; quested
action. On return,; sockaddr structures
are converted into old; style (no sa_len
member).
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-topoint interface whose remote (``destination'') address is; addr.; ifa_ifwithnet() returns the most specific interface address; which matches
the specified address, addr, subject to its configured net; mask, or a
point-to-point interface address whose remote address is; addr if one is
found.; ifaof_ifpforaddr() returns the most specific address config; ured on interface ifp which matches address addr, subject to its config; ured netmask.
If the interface is point-to-point, only an interface ad; dress whose
remote address is precisely addr will be returned.; All of these functions return a null pointer if no such ad; dress can be
found.
Interface Multicast Address Functions: The if_addmulti(), if_delmulti(), and ifmaof_ifpforaddr(); functions provide support for requesting and relinquishing multicast; group memberships, and for querying an interface's membership list, re; spectively.
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 per; forms the following four-step process:

1. Call the interface's if_resolvemulti() entry; point to determine the link-layer address, if any, correspond
ing to this membership request, and also to give the link
layer an opportunity 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 interface'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 suc
cess, or a standard error number on failure.
The ifmaof_ifpforaddr() function examines the membership
list of interface ifp for an address matching addr, and returns a pointer
to that struct ifmultiaddr if one is found, else it returns a null
pointer.

AUTHORS

This manual page was written by Garrett A. Wollman.
BSD June 10, 2005

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See also

ifnet(9)

NAME

SYNOPSIS

DATA STRUCTURES

FUNCTIONS

SEE ALSO

AUTHORS