netdevice(7) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | NOTES | BUGS | SEE ALSO | COLOPHON

NETDEVICE(7)            Linux Programmer's Manual           NETDEVICE(7)

NAME         top

       netdevice - low-level access to Linux network devices

SYNOPSIS         top

       #include <sys/ioctl.h>
       #include <net/if.h>

DESCRIPTION         top

       This man page describes the sockets interface which is used to
       configure network devices.

       Linux supports some standard ioctls to configure network devices.
       They can be used on any socket's file descriptor regardless of
       the family or type.  Most of them pass an ifreq structure:

           struct ifreq {
               char ifr_name[IFNAMSIZ]; /* Interface name */
               union {
                   struct sockaddr ifr_addr;
                   struct sockaddr ifr_dstaddr;
                   struct sockaddr ifr_broadaddr;
                   struct sockaddr ifr_netmask;
                   struct sockaddr ifr_hwaddr;
                   short           ifr_flags;
                   int             ifr_ifindex;
                   int             ifr_metric;
                   int             ifr_mtu;
                   struct ifmap    ifr_map;
                   char            ifr_slave[IFNAMSIZ];
                   char            ifr_newname[IFNAMSIZ];
                   char           *ifr_data;
               };
           };

       AF_INET6 is an exception.  It passes an in6_ifreq structure:

           struct in6_ifreq {
               struct in6_addr     ifr6_addr;
               u32                 ifr6_prefixlen;
               int                 ifr6_ifindex; /* Interface index */
           };

       Normally, the user specifies which device to affect by setting
       ifr_name to the name of the interface or ifr6_ifindex to the
       index of the interface.  All other members of the structure may
       share memory.

   Ioctls
       If an ioctl is marked as privileged, then using it requires an
       effective user ID of 0 or the CAP_NET_ADMIN capability.  If this
       is not the case, EPERM will be returned.

       SIOCGIFNAME
              Given the ifr_ifindex, return the name of the interface in
              ifr_name.  This is the only ioctl which returns its result
              in ifr_name.

       SIOCGIFINDEX
              Retrieve the interface index of the interface into
              ifr_ifindex.

       SIOCGIFFLAGS, SIOCSIFFLAGS
              Get or set the active flag word of the device.  ifr_flags
              contains a bit mask of the following values:

                                      Device flags
              IFF_UP            Interface is running.
              IFF_BROADCAST     Valid broadcast address set.
              IFF_DEBUG         Internal debugging flag.
              IFF_LOOPBACK      Interface is a loopback interface.
              IFF_POINTOPOINT   Interface is a point-to-point link.
              IFF_RUNNING       Resources allocated.
              IFF_NOARP         No arp protocol, L2 destination address not
                                set.
              IFF_PROMISC       Interface is in promiscuous mode.
              IFF_NOTRAILERS    Avoid use of trailers.
              IFF_ALLMULTI      Receive all multicast packets.
              IFF_MASTER        Master of a load balancing bundle.
              IFF_SLAVE         Slave of a load balancing bundle.
              IFF_MULTICAST     Supports multicast
              IFF_PORTSEL       Is able to select media type via ifmap.
              IFF_AUTOMEDIA     Auto media selection active.
              IFF_DYNAMIC       The addresses are lost when the interface
                                goes down.
              IFF_LOWER_UP      Driver signals L1 up (since Linux 2.6.17)
              IFF_DORMANT       Driver signals dormant (since Linux 2.6.17)
              IFF_ECHO          Echo sent packets (since Linux 2.6.25)

       Setting the active flag word is a privileged operation, but any
       process may read it.

       SIOCGIFPFLAGS, SIOCSIFPFLAGS
              Get or set extended (private) flags for the device.
              ifr_flags contains a bit mask of the following values:

                                      Private flags
              IFF_802_1Q_VLAN      Interface is 802.1Q VLAN device.
              IFF_EBRIDGE          Interface is Ethernet bridging device.
              IFF_SLAVE_INACTIVE   Interface is inactive bonding slave.
              IFF_MASTER_8023AD    Interface is 802.3ad bonding master.
              IFF_MASTER_ALB       Interface is balanced-alb bonding master.
              IFF_BONDING          Interface is a bonding master or slave.
              IFF_SLAVE_NEEDARP    Interface needs ARPs for validation.
              IFF_ISATAP           Interface is RFC4214 ISATAP interface.

       Setting the extended (private) interface flags is a privileged
       operation.

       SIOCGIFADDR, SIOCSIFADDR, SIOCDIFADDR
              Get, set, or delete the address of the device using
              ifr_addr, or ifr6_addr with ifr6_prefixlen.  Setting or
              deleting the interface address is a privileged operation.
              For compatibility, SIOCGIFADDR returns only AF_INET
              addresses, SIOCSIFADDR accepts AF_INET and AF_INET6
              addresses, and SIOCDIFADDR deletes only AF_INET6
              addresses.  A AF_INET address can be deleted by setting it
              to zero via SIOCSIFADDR.

       SIOCGIFDSTADDR, SIOCSIFDSTADDR
              Get or set the destination address of a point-to-point
              device using ifr_dstaddr.  For compatibility, only AF_INET
              addresses are accepted or returned.  Setting the
              destination address is a privileged operation.

       SIOCGIFBRDADDR, SIOCSIFBRDADDR
              Get or set the broadcast address for a device using
              ifr_brdaddr.  For compatibility, only AF_INET addresses
              are accepted or returned.  Setting the broadcast address
              is a privileged operation.

       SIOCGIFNETMASK, SIOCSIFNETMASK
              Get or set the network mask for a device using
              ifr_netmask.  For compatibility, only AF_INET addresses
              are accepted or returned.  Setting the network mask is a
              privileged operation.

       SIOCGIFMETRIC, SIOCSIFMETRIC
              Get or set the metric of the device using ifr_metric.
              This is currently not implemented; it sets ifr_metric to 0
              if you attempt to read it and returns EOPNOTSUPP if you
              attempt to set it.

       SIOCGIFMTU, SIOCSIFMTU
              Get or set the MTU (Maximum Transfer Unit) of a device
              using ifr_mtu.  Setting the MTU is a privileged operation.
              Setting the MTU to too small values may cause kernel
              crashes.

       SIOCGIFHWADDR, SIOCSIFHWADDR
              Get or set the hardware address of a device using
              ifr_hwaddr.  The hardware address is specified in a struct
              sockaddr.  sa_family contains the ARPHRD_* device type,
              sa_data the L2 hardware address starting from byte 0.
              Setting the hardware address is a privileged operation.

       SIOCSIFHWBROADCAST
              Set the hardware broadcast address of a device from
              ifr_hwaddr.  This is a privileged operation.

       SIOCGIFMAP, SIOCSIFMAP
              Get or set the interface's hardware parameters using
              ifr_map.  Setting the parameters is a privileged
              operation.

                  struct ifmap {
                      unsigned long   mem_start;
                      unsigned long   mem_end;
                      unsigned short  base_addr;
                      unsigned char   irq;
                      unsigned char   dma;
                      unsigned char   port;
                  };

              The interpretation of the ifmap structure depends on the
              device driver and the architecture.

       SIOCADDMULTI, SIOCDELMULTI
              Add an address to or delete an address from the device's
              link layer multicast filters using ifr_hwaddr.  These are
              privileged operations.  See also packet(7) for an
              alternative.

       SIOCGIFTXQLEN, SIOCSIFTXQLEN
              Get or set the transmit queue length of a device using
              ifr_qlen.  Setting the transmit queue length is a
              privileged operation.

       SIOCSIFNAME
              Changes the name of the interface specified in ifr_name to
              ifr_newname.  This is a privileged operation.  It is
              allowed only when the interface is not up.

       SIOCGIFCONF
              Return a list of interface (network layer) addresses.
              This currently means only addresses of the AF_INET (IPv4)
              family for compatibility.  Unlike the others, this ioctl
              passes an ifconf structure:

                  struct ifconf {
                      int               ifc_len; /* size of buffer */
                      union {
                          char         *ifc_buf; /* buffer address */
                          struct ifreq *ifc_req; /* array of structures */
                      };
                  };

              If ifc_req is NULL, SIOCGIFCONF returns the necessary
              buffer size in bytes for receiving all available addresses
              in ifc_len.  Otherwise, ifc_req contains a pointer to an
              array of ifreq structures to be filled with all currently
              active L3 interface addresses.  ifc_len contains the size
              of the array in bytes.  Within each ifreq structure,
              ifr_name will receive the interface name, and ifr_addr the
              address.  The actual number of bytes transferred is
              returned in ifc_len.

              If the size specified by ifc_len is insufficient to store
              all the addresses, the kernel will skip the exceeding ones
              and return success.  There is no reliable way of detecting
              this condition once it has occurred.  It is therefore
              recommended to either determine the necessary buffer size
              beforehand by calling SIOCGIFCONF with ifc_req set to
              NULL, or to retry the call with a bigger buffer whenever
              ifc_len upon return differs by less than sizeof(struct
              ifreq) from its original value.

              If an error occurs accessing the ifconf or ifreq
              structures, EFAULT will be returned.

       Most protocols support their own ioctls to configure protocol-
       specific interface options.  See the protocol man pages for a
       description.  For configuring IP addresses, see ip(7).

       In addition, some devices support private ioctls.  These are not
       described here.

NOTES         top

       SIOCGIFCONF and the other ioctls that accept or return only
       AF_INET socket addresses are IP-specific and perhaps should
       rather be documented in ip(7).

       The names of interfaces with no addresses or that don't have the
       IFF_RUNNING flag set can be found via /proc/net/dev.

       AF_INET6 IPv6 addresses can be read from /proc/net/if_inet6 or
       via rtnetlink(7).  Adding a new IPv6 address and deleting an
       existing IPv6 address can be done via SIOCSIFADDR and SIOCDIFADDR
       or via rtnetlink(7).  Retrieving or changing destination IPv6
       addresses of a point-to-point interface is possible only via
       rtnetlink(7).

BUGS         top

       glibc 2.1 is missing the ifr_newname macro in <net/if.h>.  Add
       the following to your program as a workaround:

           #ifndef ifr_newname
           #define ifr_newname     ifr_ifru.ifru_slave
           #endif

SEE ALSO         top

       proc(5), capabilities(7), ip(7), rtnetlink(7)

COLOPHON         top

       This page is part of release 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                          2021-03-22                   NETDEVICE(7)

Pages that refer to this page: getifaddrs(3)ip(7)ipv6(7)packet(7)rtnetlink(7)