IF(4N)

NAME
if - general properties of network interfaces

DESCRIPTION
Each network interface in a system corresponds to a path through which messages can be sent and received. A network interface usually has a hardware device associated with it, although certain interfaces such as the loopback interface, lo(4), do not.

During the autoconfiguration process at boot time, each interface that has underlying hardware support makes itself known to the system. Once the interface has acquired its address, it is expected to install a routing table entry so that messages can be routed through it. Most interfaces require some part of their address specified with an SIOCSIFADDR ioctl before they allow traffic to flow through them. On interfaces where the network-link layer address mapping is static, only the network number is taken from the ioctl; the remainder is found in a hardware specific manner. Interfaces that provide dynamic network-link layer address mapping facilities, such as 10Mb/s Ethernets using arp(4P),), use the entire address specified in the ioctl.

The following ioctl calls can be used to manipulate network interfaces. Unless specified otherwise, the request takes an ifreq structure as its parameter. This structure has the form
struct    ifreq {
    char    ifr_name[16];    /* name of interface (e.g. "ec0") */
    union {
    struct sockaddr    ifru_addr;
    struct sockaddr    ifru_dstaddr;
    struct sockaddr    ifru_broadaddr;
    short    ifru_flags;
    int    ifru_metric;
    short    ifru_mtu;
    } ifr_ifru;
#define ifr_addr    ifr_ifru.ifru_addr    /* address */
#define ifr_dstaddr    ifr_ifru.ifru_dstaddr    /* other end of p-to-p link */
#define ifr_broadaddr    ifr_ifru.ifru_broadaddr    /* broadcast address */
#define ifr_flags    ifr_ifru.ifru_flags    /* flags */
#define ifr_metric    ifr_ifru.ifru_metric    /* routing metric */
#define ifr_mtu    ifr_ifru.ifru_mtu    /* mtu */
};

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.

SIOCSIFBRDADDR
    Set broadcast address for protocol family and interface.

SIOCGIFBRDADDR
    Get broadcast address for protocol family and interface.

SIOCSIFFLAGS
    Set interface flags field. If the interface is marked down, any processes currently routing packets through the interface are notified.

SIOCGIFFLAGS
    Get interface flags.

SIOCSIFMETRIC
    Set interface routing metric. The metric is used only by user-level routers.

SIOCGIFMETRIC
    Get interface metric.

SIOCGIFCONF
    Get interface configuration list. This request takes an ifconf structure (see below) as a value-result parameter. The ifc_len field should be initially set to the size of the buffer pointed to by ifc_buf. On return it will contain the length, in bytes, of the configuration list.

SIOCSIFMTU
    set the maximum transfer unit (mtu) of an interface

SIOCGIFMTU
    get the maximum transfer unit (mtu) of an interface /*
     * Structure used in SIOCGIFCONF request.
     * Used to retrieve interface configuration
     * for machine (useful for programs which
     * must know all networks accessible).
     */
    struct    ifconf    {
        int    ifc_len;    /* size of associated buffer */
        union    {
        caddr_t    ifcu_buf;
        struct ifreq    *ifcu_req;
        } ifc_ifcu;
    #define ifc_buf    ifc_ifcu.ifcu_buf    /* buffer address */
    #define ifc_req    ifc_ifcu.ifcu_req    /* array of structures returned */
    };

SEE ALSO
arp(4P), ec(4S), en(4S), lo(4)