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.

SEE ALSO

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), rten
try(9)
Gary R. Wright and W. Richard Stevens, TCP/IP Illustrated,
Vol. 2,
Addison-Wesley, ISBN 0-201-63354-X.

AUTHORS

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