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 deter

mine 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

docs.sk

comprehensive documentation repository

See also

ifnet(9)

NAME

SYNOPSIS

DATA STRUCTURES

FUNCTIONS

SEE ALSO

AUTHORS