1NETDEVICE(7) Linux Programmer's 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. They 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 struct ifconf {
40 int ifc_len; /* size of buffer */
41 union {
42 char * ifc_buf; /* buffer address */
43 struct ifreq * ifc_req; /* array of structures */
44 };
45 };
46 Normally, the user specifies which device to affect by setting ifr_name
48 to the name of the interface. All other members of the structure may
49 share memory.
50
53 If an ioctl is marked as privileged then using it requires an effective
54 user ID of 0 or the CAP_NET_ADMIN capability. If this is not the case
55 EPERM will be returned.
56 SIOCGIFNAME
59 Given the ifr_ifindex, return the name of the interface in
60 ifr_name. This is the only ioctl which returns its result in
61 ifr_name.
62 SIOCGIFINDEX
65 Retrieve the interface index of the interface into ifr_ifindex.
66 SIOCGIFFLAGS, SIOCSIFFLAGS
69 Get or set the active flag word of the device. ifr_flags con‐
70 tains a bitmask of the following values:
71 Device flags
74 IFF_UP Interface is running.
75 IFF_BROADCAST Valid broadcast address set.
76 IFF_DEBUG Internal debugging flag.
77 IFF_LOOPBACK Interface is a loopback interface.
78 IFF_POINTOPOINT Interface is a point-to-point link.
79 IFF_RUNNING Resources allocated.
80 IFF_NOARP No arp protocol, L2 destination address not set.
81 IFF_PROMISC Interface is in promiscuous mode.
82 IFF_NOTRAILERS Avoid use of trailers.
83 IFF_ALLMULTI Receive all multicast packets.
84 IFF_MASTER Master of a load balancing bundle.
85 IFF_SLAVE Slave of a load balancing bundle.
86 IFF_MULTICAST Supports multicast
87 IFF_PORTSEL Is able to select media type via ifmap.
88 IFF_AUTOMEDIA Auto media selection active.
89 IFF_DYNAMIC The addresses are lost when the interface goes
90 down.
91 Setting the active flag word is a privileged operation, but any
93 process may read it.
94 SIOCGIFMETRIC, SIOCSIFMETRIC
96 Get or set the metric of the device using ifr_metric. This is
97 currently not implemented; it sets ifr_metric to 0 if you
98 attempt to read it and returns EOPNOTSUPP if you attempt to set
99 it.
100 SIOCGIFMTU, SIOCSIFMTU
102 Get or set the MTU (Maximum Transfer Unit) of a device using
103 ifr_mtu. Setting the MTU is a privileged operation. Setting the
104 MTU to too small values may cause kernel crashes.
105 SIOCGIFHWADDR, SIOCSIFHWADDR
107 Get or set the hardware address of a device using ifr_hwaddr.
108 The hardware address is specified in a struct sockaddr. sa_fam‐
109 ily contains the ARPHRD_* device type, sa_data the L2 hardware
110 address starting from byte 0. Setting the hardware address is a
111 privileged operation.
112 SIOCSIFHWBROADCAST
114 Set the hardware broadcast address of a device from ifr_hwaddr.
115 This is a privileged operation.
116 SIOCGIFMAP, SIOCSIFMAP
118 Get or set the interface's hardware parameters using ifr_map.
119 Setting the parameters is a privileged operation.
120 struct ifmap {
122 unsigned long mem_start;
123 unsigned long mem_end;
124 unsigned short base_addr;
125 unsigned char irq;
126 unsigned char dma;
127 unsigned char port;
128 };
129 The interpretation of the ifmap structure depends on the device
131 driver and the architecture.
132 SIOCADDMULTI, SIOCDELMULTI
134 Add an address to or delete an address from the device's link
135 layer multicast filters using ifr_hwaddr. These are privileged
136 operations. See also packet(7) for an alternative.
137 SIOCGIFTXQLEN, SIOCSIFTXQLEN
139 Get or set the transmit queue length of a device using ifr_qlen.
140 Setting the transmit queue length is a privileged operation.
141 SIOCSIFNAME
143 Changes the name of the interface specified in ifr_name to
144 ifr_newname. This is a privileged operation. It is only allowed
145 when the interface is not up.
146 SIOCGIFCONF
148 Return a list of interface (transport layer) addresses. This
149 currently means only addresses of the AF_INET (IPv4) family for
150 compatibility. The user passes a ifconf structure as argument
151 to the ioctl. It contains a pointer to an array of ifreq struc‐
152 tures in ifc_req and its length in bytes in ifc_len. The kernel
153 fills the ifreqs with all current L3 interface addresses that
154 are running: ifr_name contains the interface name (eth0:1 etc.),
155 ifr_addr the address. The kernel returns with the actual length
156 in ifc_len. If ifc_len is equal to the original length the buf‐
157 fer probably has overflowed and you should retry with a bigger
158 buffer to get all addresses. When no error occurs the ioctl
159 returns 0; otherwise -1. Overflow is not an error.
160 Most protocols support their own ioctls to configure protocol specific
162 interface options. See the protocol man pages for a description. For
163 configuring IP addresses see ip(7).
164 In addition some devices support private ioctls. These are not
166 described here.
167
169 Strictly speaking, SIOCGIFCONF is IP specific and belongs in ip(7).
170 The names of interfaces with no addresses or that don't have the
172 IFF_RUNNING flag set can be found via /proc/net/dev.
173 Local IPv6 IP addresses can be found via /proc/net or via rtnetlink(7).
175
177 glibc 2.1 is missing the ifr_newname macro in net/if.h. Add the follow‐
178 ing to your program as a workaround:
179 #ifndef ifr_newname
181 #define ifr_newname ifr_ifru.ifru_slave
182 #endif
183
185 capabilities(7), ip(7), proc(7), rtnetlink(7)
186Linux Man Page 1999-05-02 NETDEVICE(7)