1NETDEVICE(7)               Linux Programmer's Manual              NETDEVICE(7)
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NAME

6       netdevice - low-level access to Linux network devices
7

SYNOPSIS

9       #include <sys/ioctl.h>
10       #include <net/if.h>
11

DESCRIPTION

13       This  man page describes the sockets interface which is used to config‐
14       ure network devices.
15
16       Linux supports some standard ioctls to configure network devices.  They
17       can be used on any socket's file descriptor regardless of the family or
18       type.  Most of them pass an ifreq structure:
19
20           struct ifreq {
21               char ifr_name[IFNAMSIZ]; /* Interface name */
22               union {
23                   struct sockaddr ifr_addr;
24                   struct sockaddr ifr_dstaddr;
25                   struct sockaddr ifr_broadaddr;
26                   struct sockaddr ifr_netmask;
27                   struct sockaddr ifr_hwaddr;
28                   short           ifr_flags;
29                   int             ifr_ifindex;
30                   int             ifr_metric;
31                   int             ifr_mtu;
32                   struct ifmap    ifr_map;
33                   char            ifr_slave[IFNAMSIZ];
34                   char            ifr_newname[IFNAMSIZ];
35                   char           *ifr_data;
36               };
37           };
38
39       Normally, the user specifies which device to affect by setting ifr_name
40       to  the  name of the interface.  All other members of the structure may
41       share memory.
42
43   Ioctls
44       If an ioctl is marked as privileged, then using it requires  an  effec‐
45       tive  user ID of 0 or the CAP_NET_ADMIN capability.  If this is not the
46       case, EPERM will be returned.
47
48       SIOCGIFNAME
49              Given the ifr_ifindex, return  the  name  of  the  interface  in
50              ifr_name.   This  is  the only ioctl which returns its result in
51              ifr_name.
52
53       SIOCGIFINDEX
54              Retrieve the interface index of the interface into ifr_ifindex.
55
56       SIOCGIFFLAGS, SIOCSIFFLAGS
57              Get or set the active flag word of the device.   ifr_flags  con‐
58              tains a bit mask of the following values:
59
60                                      Device flags
61              IFF_UP            Interface is running.
62              IFF_BROADCAST     Valid broadcast address set.
63              IFF_DEBUG         Internal debugging flag.
64              IFF_LOOPBACK      Interface is a loopback interface.
65              IFF_POINTOPOINT   Interface is a point-to-point link.
66
67              IFF_RUNNING       Resources allocated.
68              IFF_NOARP         No arp protocol, L2 destination address not
69                                set.
70              IFF_PROMISC       Interface is in promiscuous mode.
71              IFF_NOTRAILERS    Avoid use of trailers.
72              IFF_ALLMULTI      Receive all multicast packets.
73              IFF_MASTER        Master of a load balancing bundle.
74              IFF_SLAVE         Slave of a load balancing bundle.
75              IFF_MULTICAST     Supports multicast
76              IFF_PORTSEL       Is able to select media type via ifmap.
77              IFF_AUTOMEDIA     Auto media selection active.
78              IFF_DYNAMIC       The addresses are lost when the interface
79                                goes down.
80              IFF_LOWER_UP      Driver signals L1 up (since Linux 2.6.17)
81              IFF_DORMANT       Driver signals dormant (since Linux 2.6.17)
82              IFF_ECHO          Echo sent packets (since Linux 2.6.25)
83
84       Setting the active flag word is a privileged operation, but any process
85       may read it.
86
87       SIOCGIFPFLAGS, SIOCSIFPFLAGS
88              Get or set extended (private) flags for the  device.   ifr_flags
89              contains a bit mask of the following values:
90
91                                      Private flags
92              IFF_802_1Q_VLAN      Interface is 802.1Q VLAN device.
93              IFF_EBRIDGE          Interface is Ethernet bridging device.
94              IFF_SLAVE_INACTIVE   Interface is inactive bonding slave.
95              IFF_MASTER_8023AD    Interface is 802.3ad bonding master.
96              IFF_MASTER_ALB       Interface is balanced-alb bonding master.
97              IFF_BONDING          Interface is a bonding master or slave.
98              IFF_SLAVE_NEEDARP    Interface needs ARPs for validation.
99              IFF_ISATAP           Interface is RFC4214 ISATAP interface.
100
101       Setting  the  extended (private) interface flags is a privileged opera‐
102       tion.
103
104       SIOCGIFADDR, SIOCSIFADDR
105              Get or set the address of the device  using  ifr_addr.   Setting
106              the  interface  address is a privileged operation.  For compati‐
107              bility, only AF_INET addresses are accepted or returned.
108
109       SIOCGIFDSTADDR, SIOCSIFDSTADDR
110              Get or set the destination address of  a  point-to-point  device
111              using  ifr_dstaddr.   For  compatibility, only AF_INET addresses
112              are accepted or returned.  Setting the destination address is  a
113              privileged operation.
114
115       SIOCGIFBRDADDR, SIOCSIFBRDADDR
116              Get or set the broadcast address for a device using ifr_brdaddr.
117              For compatibility, only AF_INET addresses are  accepted  or  re‐
118              turned.   Setting  the  broadcast address is a privileged opera‐
119              tion.
120
121       SIOCGIFNETMASK, SIOCSIFNETMASK
122              Get or set the network mask for a device using ifr_netmask.  For
123              compatibility,  only AF_INET addresses are accepted or returned.
124              Setting the network mask is a privileged operation.
125
126       SIOCGIFMETRIC, SIOCSIFMETRIC
127              Get or set the metric of the device using ifr_metric.   This  is
128              currently  not  implemented;  it sets ifr_metric to 0 if you at‐
129              tempt to read it and returns EOPNOTSUPP if you  attempt  to  set
130              it.
131
132       SIOCGIFMTU, SIOCSIFMTU
133              Get  or  set  the  MTU (Maximum Transfer Unit) of a device using
134              ifr_mtu.  Setting the MTU is a  privileged  operation.   Setting
135              the MTU to too small values may cause kernel crashes.
136
137       SIOCGIFHWADDR, SIOCSIFHWADDR
138              Get  or  set  the hardware address of a device using ifr_hwaddr.
139              The hardware address is specified in a struct sockaddr.  sa_fam‐
140              ily  contains  the ARPHRD_* device type, sa_data the L2 hardware
141              address starting from byte 0.  Setting the hardware address is a
142              privileged operation.
143
144       SIOCSIFHWBROADCAST
145              Set  the hardware broadcast address of a device from ifr_hwaddr.
146              This is a privileged operation.
147
148       SIOCGIFMAP, SIOCSIFMAP
149              Get or set the interface's hardware  parameters  using  ifr_map.
150              Setting the parameters is a privileged operation.
151
152                  struct ifmap {
153                      unsigned long   mem_start;
154                      unsigned long   mem_end;
155                      unsigned short  base_addr;
156                      unsigned char   irq;
157                      unsigned char   dma;
158                      unsigned char   port;
159                  };
160
161              The  interpretation of the ifmap structure depends on the device
162              driver and the architecture.
163
164       SIOCADDMULTI, SIOCDELMULTI
165              Add an address to or delete an address from  the  device's  link
166              layer  multicast filters using ifr_hwaddr.  These are privileged
167              operations.  See also packet(7) for an alternative.
168
169       SIOCGIFTXQLEN, SIOCSIFTXQLEN
170              Get or set the transmit queue length of a device using ifr_qlen.
171              Setting the transmit queue length is a privileged operation.
172
173       SIOCSIFNAME
174              Changes  the  name  of  the  interface  specified in ifr_name to
175              ifr_newname.  This is a privileged  operation.   It  is  allowed
176              only when the interface is not up.
177
178       SIOCGIFCONF
179              Return a list of interface (network layer) addresses.  This cur‐
180              rently means only addresses of the  AF_INET  (IPv4)  family  for
181              compatibility.   Unlike  the others, this ioctl passes an ifconf
182              structure:
183
184                  struct ifconf {
185                      int                 ifc_len; /* size of buffer */
186                      union {
187                          char           *ifc_buf; /* buffer address */
188                          struct ifreq   *ifc_req; /* array of structures */
189                      };
190                  };
191
192              If ifc_req is NULL, SIOCGIFCONF  returns  the  necessary  buffer
193              size  in bytes for receiving all available addresses in ifc_len.
194              Otherwise, ifc_req contains a  pointer  to  an  array  of  ifreq
195              structures  to  be filled with all currently active L3 interface
196              addresses.  ifc_len contains the size of  the  array  in  bytes.
197              Within each ifreq structure, ifr_name will receive the interface
198              name, and ifr_addr the address.   The  actual  number  of  bytes
199              transferred is returned in ifc_len.
200
201              If  the  size  specified by ifc_len is insufficient to store all
202              the addresses, the kernel will skip the exceeding ones  and  re‐
203              turn success.  There is no reliable way of detecting this condi‐
204              tion once it has occurred.  It is therefore recommended  to  ei‐
205              ther  determine  the necessary buffer size beforehand by calling
206              SIOCGIFCONF with ifc_req set to NULL, or to retry the call  with
207              a  bigger  buffer  whenever  ifc_len upon return differs by less
208              than sizeof(struct ifreq) from its original value.
209
210              If an error occurs accessing the  ifconf  or  ifreq  structures,
211              EFAULT will be returned.
212
213       Most  protocols support their own ioctls to configure protocol-specific
214       interface options.  See the protocol man pages for a description.   For
215       configuring IP addresses, see ip(7).
216
217       In  addition,  some  devices support private ioctls.  These are not de‐
218       scribed here.
219

NOTES

221       SIOCGIFCONF and the other ioctls that accept  or  return  only  AF_INET
222       socket  addresses  are  IP-specific  and perhaps should rather be docu‐
223       mented in ip(7).
224
225       The names of interfaces with  no  addresses  or  that  don't  have  the
226       IFF_RUNNING flag set can be found via /proc/net/dev.
227
228       Local IPv6 IP addresses can be found via /proc/net or via rtnetlink(7).
229

BUGS

231       glibc 2.1 is missing the ifr_newname macro in <net/if.h>.  Add the fol‐
232       lowing to your program as a workaround:
233
234           #ifndef ifr_newname
235           #define ifr_newname     ifr_ifru.ifru_slave
236           #endif
237

SEE ALSO

239       proc(5), capabilities(7), ip(7), rtnetlink(7)
240

COLOPHON

242       This page is part of release 5.10 of the Linux  man-pages  project.   A
243       description  of  the project, information about reporting bugs, and the
244       latest    version    of    this    page,    can     be     found     at
245       https://www.kernel.org/doc/man-pages/.
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249Linux                             2020-08-13                      NETDEVICE(7)
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