1netdevice(7) Miscellaneous Information Manual netdevice(7)
2
6 netdevice - low-level access to Linux network devices
7
9 #include <sys/ioctl.h>
10 #include <net/if.h>
11
13 This man page describes the sockets interface which is used to config‐
14 ure network devices.
15 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 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 AF_INET6 is an exception. It passes an in6_ifreq structure:
40 struct in6_ifreq {
42 struct in6_addr ifr6_addr;
43 u32 ifr6_prefixlen;
44 int ifr6_ifindex; /* Interface index */
45 };
46 Normally, the user specifies which device to affect by setting ifr_name
48 to the name of the interface or ifr6_ifindex to the index of the inter‐
49 face. All other members of the structure may share memory.
50 Ioctls
52 If an ioctl is marked as privileged, then using it requires an effec‐
53 tive user ID of 0 or the CAP_NET_ADMIN capability. If this is not the
54 case, EPERM will be returned.
55 SIOCGIFNAME
57 Given the ifr_ifindex, return the name of the interface in
58 ifr_name. This is the only ioctl which returns its result in
59 ifr_name.
60 SIOCGIFINDEX
62 Retrieve the interface index of the interface into ifr_ifindex.
63 SIOCGIFFLAGS, SIOCSIFFLAGS
65 Get or set the active flag word of the device. ifr_flags con‐
66 tains a bit mask of the following values:
67 Device flags
69 IFF_UP Interface is running.
70 IFF_BROADCAST Valid broadcast address set.
71 IFF_DEBUG Internal debugging flag.
72 IFF_LOOPBACK Interface is a loopback interface.
73 IFF_POINTOPOINT Interface is a point-to-point link.
74 IFF_RUNNING Resources allocated.
75 IFF_NOARP No arp protocol, L2 destination address not
76 set.
77 IFF_PROMISC Interface is in promiscuous mode.
78 IFF_NOTRAILERS Avoid use of trailers.
79 IFF_ALLMULTI Receive all multicast packets.
80 IFF_MASTER Master of a load balancing bundle.
81 IFF_SLAVE Slave of a load balancing bundle.
82 IFF_MULTICAST Supports multicast
83 IFF_PORTSEL Is able to select media type via ifmap.
84 IFF_AUTOMEDIA Auto media selection active.
85 IFF_DYNAMIC The addresses are lost when the interface
86 goes down.
87 IFF_LOWER_UP Driver signals L1 up (since Linux 2.6.17)
88 IFF_DORMANT Driver signals dormant (since Linux 2.6.17)
89 IFF_ECHO Echo sent packets (since Linux 2.6.25)
90 Setting the active flag word is a privileged operation, but any process
92 may read it.
93 SIOCGIFPFLAGS, SIOCSIFPFLAGS
95 Get or set extended (private) flags for the device. ifr_flags
96 contains a bit mask of the following values:
97 Private flags
99 IFF_802_1Q_VLAN Interface is 802.1Q VLAN device.
100 IFF_EBRIDGE Interface is Ethernet bridging device.
101 IFF_SLAVE_INACTIVE Interface is inactive bonding slave.
102 IFF_MASTER_8023AD Interface is 802.3ad bonding master.
103 IFF_MASTER_ALB Interface is balanced-alb bonding master.
104 IFF_BONDING Interface is a bonding master or slave.
105 IFF_SLAVE_NEEDARP Interface needs ARPs for validation.
106 IFF_ISATAP Interface is RFC4214 ISATAP interface.
107 Setting the extended (private) interface flags is a privileged opera‐
109 tion.
110 SIOCGIFADDR, SIOCSIFADDR, SIOCDIFADDR
112 Get, set, or delete the address of the device using ifr_addr, or
113 ifr6_addr with ifr6_prefixlen. Setting or deleting the inter‐
114 face address is a privileged operation. For compatibility,
115 SIOCGIFADDR returns only AF_INET addresses, SIOCSIFADDR accepts
116 AF_INET and AF_INET6 addresses, and SIOCDIFADDR deletes only
117 AF_INET6 addresses. A AF_INET address can be deleted by setting
118 it to zero via SIOCSIFADDR.
119 SIOCGIFDSTADDR, SIOCSIFDSTADDR
121 Get or set the destination address of a point-to-point device
122 using ifr_dstaddr. For compatibility, only AF_INET addresses
123 are accepted or returned. Setting the destination address is a
124 privileged operation.
125 SIOCGIFBRDADDR, SIOCSIFBRDADDR
127 Get or set the broadcast address for a device using ifr_brdaddr.
128 For compatibility, only AF_INET addresses are accepted or re‐
129 turned. Setting the broadcast address is a privileged opera‐
130 tion.
131 SIOCGIFNETMASK, SIOCSIFNETMASK
133 Get or set the network mask for a device using ifr_netmask. For
134 compatibility, only AF_INET addresses are accepted or returned.
135 Setting the network mask is a privileged operation.
136 SIOCGIFMETRIC, SIOCSIFMETRIC
138 Get or set the metric of the device using ifr_metric. This is
139 currently not implemented; it sets ifr_metric to 0 if you at‐
140 tempt to read it and returns EOPNOTSUPP if you attempt to set
141 it.
142 SIOCGIFMTU, SIOCSIFMTU
144 Get or set the MTU (Maximum Transfer Unit) of a device using
145 ifr_mtu. Setting the MTU is a privileged operation. Setting
146 the MTU to too small values may cause kernel crashes.
147 SIOCGIFHWADDR, SIOCSIFHWADDR
149 Get or set the hardware address of a device using ifr_hwaddr.
150 The hardware address is specified in a struct sockaddr. sa_fam‐
151 ily contains the ARPHRD_* device type, sa_data the L2 hardware
152 address starting from byte 0. Setting the hardware address is a
153 privileged operation.
154 SIOCSIFHWBROADCAST
156 Set the hardware broadcast address of a device from ifr_hwaddr.
157 This is a privileged operation.
158 SIOCGIFMAP, SIOCSIFMAP
160 Get or set the interface's hardware parameters using ifr_map.
161 Setting the parameters is a privileged operation.
162 struct ifmap {
164 unsigned long mem_start;
165 unsigned long mem_end;
166 unsigned short base_addr;
167 unsigned char irq;
168 unsigned char dma;
169 unsigned char port;
170 };
171 The interpretation of the ifmap structure depends on the device
173 driver and the architecture.
174 SIOCADDMULTI, SIOCDELMULTI
176 Add an address to or delete an address from the device's link
177 layer multicast filters using ifr_hwaddr. These are privileged
178 operations. See also packet(7) for an alternative.
179 SIOCGIFTXQLEN, SIOCSIFTXQLEN
181 Get or set the transmit queue length of a device using ifr_qlen.
182 Setting the transmit queue length is a privileged operation.
183 SIOCSIFNAME
185 Changes the name of the interface specified in ifr_name to
186 ifr_newname. This is a privileged operation. It is allowed
187 only when the interface is not up.
188 SIOCGIFCONF
190 Return a list of interface (network layer) addresses. This cur‐
191 rently means only addresses of the AF_INET (IPv4) family for
192 compatibility. Unlike the others, this ioctl passes an ifconf
193 structure:
194 struct ifconf {
196 int ifc_len; /* size of buffer */
197 union {
198 char *ifc_buf; /* buffer address */
199 struct ifreq *ifc_req; /* array of structures */
200 };
201 };
202 If ifc_req is NULL, SIOCGIFCONF returns the necessary buffer
204 size in bytes for receiving all available addresses in ifc_len.
205 Otherwise, ifc_req contains a pointer to an array of ifreq
206 structures to be filled with all currently active L3 interface
207 addresses. ifc_len contains the size of the array in bytes.
208 Within each ifreq structure, ifr_name will receive the interface
209 name, and ifr_addr the address. The actual number of bytes
210 transferred is returned in ifc_len.
211 If the size specified by ifc_len is insufficient to store all
213 the addresses, the kernel will skip the exceeding ones and re‐
214 turn success. There is no reliable way of detecting this condi‐
215 tion once it has occurred. It is therefore recommended to ei‐
216 ther determine the necessary buffer size beforehand by calling
217 SIOCGIFCONF with ifc_req set to NULL, or to retry the call with
218 a bigger buffer whenever ifc_len upon return differs by less
219 than sizeof(struct ifreq) from its original value.
220 If an error occurs accessing the ifconf or ifreq structures,
222 EFAULT will be returned.
223 Most protocols support their own ioctls to configure protocol-specific
225 interface options. See the protocol man pages for a description. For
226 configuring IP addresses, see ip(7).
227 In addition, some devices support private ioctls. These are not de‐
229 scribed here.
230
232 SIOCGIFCONF and the other ioctls that accept or return only AF_INET
233 socket addresses are IP-specific and perhaps should rather be docu‐
234 mented in ip(7).
235 The names of interfaces with no addresses or that don't have the
237 IFF_RUNNING flag set can be found via /proc/net/dev.
238 AF_INET6 IPv6 addresses can be read from /proc/net/if_inet6 or via rt‐
240 netlink(7). Adding a new IPv6 address and deleting an existing IPv6
241 address can be done via SIOCSIFADDR and SIOCDIFADDR or via rt‐
242 netlink(7). Retrieving or changing destination IPv6 addresses of a
243 point-to-point interface is possible only via rtnetlink(7).
244
246 glibc 2.1 is missing the ifr_newname macro in <net/if.h>. Add the fol‐
247 lowing to your program as a workaround:
248 #ifndef ifr_newname
250 #define ifr_newname ifr_ifru.ifru_slave
251 #endif
252
254 proc(5), capabilities(7), ip(7), rtnetlink(7)
255Linux man-pages 6.04 2022-12-15 netdevice(7)