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 implemented 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 I_LINK ioctl() call. This may be initiated by the kernel at boot time or by a user program some time after the system 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 mapping 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 automatically when an interface's address is set.

IOCTLS

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 ifr_name.  The remainder may be interface specific. */

struct  ifreq {
#define IFNAMSIZ     16
    char         ifr_name[IFNAMSIZ];          /* if name, e.g. "emd1" */
    union {
         struct  sockaddr ifru_addr;
         struct  sockaddr ifru_dstaddr;
         char    ifru_oname[IFNAMSIZ];        /* other if name */
         struct  sockaddr ifru_broadaddr;
         short   ifru_flags;
         int     ifru_metric;
         char    ifru_data[1];                /* interface dependent data */

         char    ifru_enaddr[6];
    } 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_oname     ifr_ifru.ifru_oname     /* other if name */
#define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
#define ifr_flags     ifr_ifru.ifru_flags     /* flags */
#define ifr_metric    ifr_ifru.ifru_metric    /* metric */
#define ifr_data      ifr_ifru.ifru_data      /* for use by interface */
#define ifr_enaddr    ifr_ifru.ifru_enaddr    /* 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 packets through the interface are notified.

SIOCGIFFLAGS Get interface flags.

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.

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     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 */
     };

SIOCSIFNAME

Set the name of the interface.

SEE ALSO

arp(7), ip(7), lo(7).