man > netdevice(7)

netdevice(7)                      Miscellaneous Information Manual                      netdevice(7)

NAME
       netdevice - low-level access to Linux network devices

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

DESCRIPTION
       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 struc‐
       ture:

           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  destina‐
              tion 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 imple‐
              mented; 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 priv‐
              ileged 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 archi‐
              tecture.

       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 alter‐
              native.

       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 ad‐
              dresses 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 receiv‐
              ing 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 ad‐
              dresses.  ifc_len contains the size of the array in bytes.  Within each  ifreq  struc‐
              ture,  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  ker‐
              nel  will skip the exceeding ones and return success.  There is no reliable way of de‐
              tecting 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 dif‐
              fers 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
       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 SIOCD‐
       IFADDR or via rtnetlink(7).  Retrieving or changing destination IPv6 addresses of a point-to-
       point interface is possible only via rtnetlink(7).

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

Linux man-pages 6.7                          2023-10-31                                 netdevice(7)