IF(4N)

NAME
if - general properties of network interfaces

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

At boot time each interface which has underlying hardware support makes itself known to the system during the autoconfiguration process. Once the interface has acquired its address it is expected to install a routing table entry so that messages may be routed through it. Most interfaces require some part of their address specified with an SIOCSIFADDR ioctl before they will 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. On interfaces which provide dynamic network-link layer address mapping facilities (for example, 10Mb/s Ethernets using arp(4P),), the entire address specified in the ioctl is used.

The following ioctl calls may 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;
    		short	ifru_flags;
    	} 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_flags		ifr_ifru.ifru_flags	/* flags */
    };

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.
    /*
     * 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), lo(4)