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.
The following
ioctl(2) calls may be used to manipulate network interfaces. The
ioctl(2) is made on a socket (typically of type
SOCK_DGRAM) in the desired domain. Most of the requests supported in earlier releases take an
ifreq structure as its parameter. This structure has the form
struct ifreq {
#define IFNAMSIZ 16
char ifr_name[IFNAMSIZ]; /* if name, e.g. "en0" */
union {
struct sockaddr ifru_addr;
struct sockaddr ifru_dstaddr;
struct sockaddr ifru_broadaddr;
short ifru_flags;
int ifru_metric;
void *ifru_data;
} 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 /* metric */
#define ifr_data ifr_ifru.ifru_data /* for use by interface */
};
Calls which are now deprecated are:
SIOCSIFADDR
Set interface address for protocol family. Following the address assignment, the ``initialization'' routine for the interface is called.
SIOCSIFDSTADDR
Set point to point address for protocol family and interface.
SIOCSIFBRDADDR
Set broadcast address for protocol family and interface.
ioctl(2) requests to obtain addresses and requests both to set and retrieve other data are still fully supported and use the
ifreq structure:
SIOCGIFADDR
Get interface address for protocol family.
SIOCGIFDSTADDR
Get point to point 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; some interfaces may be reset so that incoming packets are no longer received. When marked up again, the interface is reinitialized.
SIOCGIFFLAGS
Get interface flags.
SIOCSIFMETRIC
Set interface routing metric. The metric is used only by user-level routers.
SIOCGIFMETRIC
Get interface metric.
There are two requests that make use of a new structure:
SIOCAIFADDR
An interface may have more than one address associated with it in some protocols. This request provides a means to add additional addresses (or modify characteristics of the primary address if the default address for the address family is specified). Rather than making separate calls to set destination or broadcast addresses, or network masks (now an integral feature of multiple protocols) a separate structure,
ifaliasreq, is used to specify all three facets simultaneously (see below). One would use a slightly tailored version of this struct specific to each family (replacing each sockaddr by one of the family-specific type). Where the sockaddr itself is larger than the default size, one needs to modify the
ioctl(2) identifier itself to include the total size, as described in
ioctl(2).
SIOCDIFADDR
This requests deletes the specified address from the list associated with an interface. It also uses the ifaliasreq structure to allow for the possibility of protocols allowing multiple masks or destination addresses, and also adopts the convention that specification of the default address means to delete the first address for the interface belonging to the address family in which the original socket was opened.
Request making use of the
ifconf structure:
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 SIOC[AD]IFADDR request.
*/
struct ifaliasreq {
char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */
struct sockaddr ifra_addr;
struct sockaddr ifra_dstaddr;
#define ifra_broadaddr ifra_dstaddr
struct sockaddr ifra_mask;
};
/*
* 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 {
void *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 */
};