if(7) if(7)
NAME
if - general properties of Internet Protocol network interfaces
DESCRIPTION
A network interface is a device for sending and receiving packets on a
network. A network interface is usually a hardware device, although
certain interfaces such as the loopback interface, lo(7), are imple-
mented in software. Network interfaces used by the Internet Protocol
(IP) must be STREAMS devices conforming to the Datalink Provider
Interface (DLPI).
An interface becomes available to IP when it is linked below the IP
STREAMS device with the ILINK ioctl() call. This may be initiated by
the kernel at boot time or by a user program some time after the sys-
tem is running. Each IP interface must have a name assigned to it with
the SIOCSIFNAME ioctl(). This name is used as a unique handle on the
interface by all of the other network interface ioctl() calls. Each
interface must be assigned an IP address with the SIOCSIFADDR ioctl()
before it can be used. On interfaces where the network-to-link layer
address mapping is static, only the network number is taken from the
ioctl() request; the remainder is found in a hardware specific manner.
On interfaces which provide dynamic network-to-link layer address map-
ping facilities [for example, 10Mb/s Ethernets using arp(7)], the
entire address specified in the ioctl() is used. A routing table entry
for destinations on the network of the interface is installed automat-
ically when an interface's address is set.
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IOCTL'S
The following ioctl() calls may be used to manipulate IP network
interfaces. Unless specified otherwise, the request takes an ifreq
structure as its parameter. This structure has the form:
/* Interface request structure used for socket ioctl's. */
/* All interface ioctl's must have parameter definitions */
/* which begin with ifrname. The remainder may be */
/* interface specific. */
struct ifreq {
#define IFNAMSIZ 16
char ifrname[IFNAMSIZ]; /* if name, e.g. "emd1" */
union {
struct sockaddr ifruaddr;
struct sockaddr ifrudstaddr;
char ifruoname[IFNAMSIZ]; /* other if name */
struct sockaddr ifrubroadaddr;
short ifruflags;
int ifrumetric;
char ifrudata[1]; /* interface dependent data */
char ifruenaddr[6];
} ifrifru;
#define ifraddr ifrifru.ifruaddr /* address */
#define ifrdstaddr ifrifru.ifrudstaddr /* other end of p-to-p link */
#define ifroname ifrifru.ifruoname /* other if name */
#define ifrbroadaddr ifrifru.ifrubroadaddr /* broadcast address */
#define ifrflags ifrifru.ifruflags /* flags */
#define ifrmetric ifrifru.ifrumetric /* metric */
#define ifrdata ifrifru.ifrudata /* for use by interface */
#define ifrenaddr ifrifru.ifruenaddr /* ethernet address */
};
SIOCSIFADDR Set interface address. Following the address
assignment, the "initialization" routine for the
interface is called.
SIOCGIFADDR Get interface address.
SIOCSIFDSTADDR Set point to point address for interface.
SIOCGIFDSTADDR Get point to point address for interface.
SIOCSIFFLAGS Set interface flags field. If the interface is
marked down, any processes currently routing pack-
ets through the interface are notified.
SIOCGIFFLAGS Get interface flags.
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SIOCGIFCONF Get interface configuration list. This request
takes an ifconf structure (see below) as a value-
result parameter. The ifclen field should be ini-
tially set to the size of the buffer pointed to by
ifcbuf. On return it will contain the length, in
bytes, of the configuration list.
The ifconf structure has the form:
/*
* Structure used in SIOCGIFCONF request.
* Used to retrieve interface configuration
* for machine (useful for programs which
* must know all networks accessible).
*/
struct ifconf {
int ifclen; /* size of associated buffer */
union {
caddrt ifcubuf;
struct ifreq *ifcureq;
} ifcifcu;
#define ifcbuf ifcifcu.ifcubuf /* buffer address */
#define ifcreq ifcifcu.ifcureq /* array of structures returned */
};
SIOCSIFNAME Set the name of the interface.
SEE ALSO
arp(7), ip(7), lo(7).
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