'\" t .\" SPDX-License-Identifier: Linux-man-pages-1-para .\" .\" This man page is Copyright (C) 1999 Andi Kleen . .\" .\" $Id: netdevice.7,v 1.10 2000/08/17 10:09:54 ak Exp $ .\" .\" Modified, 2004-11-25, mtk, formatting and a few wording fixes .\" .\" Modified, 2011-11-02, , added many basic .\" but missing ioctls, such as SIOCGIFADDR. .\" .TH netdevice 7 2023-10-31 "Linux man-pages 6.7" .SH NAME netdevice \- low-level access to Linux network devices .SH SYNOPSIS .nf .B "#include " .B "#include " .fi .SH DESCRIPTION This man page describes the sockets interface which is used to configure network devices. .P 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 .I ifreq structure: .P .in +4n .EX 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; }; }; .EE .in .P .B AF_INET6 is an exception. It passes an .I in6_ifreq structure: .P .in +4n .EX struct in6_ifreq { struct in6_addr ifr6_addr; u32 ifr6_prefixlen; int ifr6_ifindex; /* Interface index */ }; .EE .in .P Normally, the user specifies which device to affect by setting .I ifr_name to the name of the interface or .I ifr6_ifindex to the index of the interface. All other members of the structure may share memory. .SS Ioctls If an ioctl is marked as privileged, then using it requires an effective user ID of 0 or the .B CAP_NET_ADMIN capability. If this is not the case, .B EPERM will be returned. .TP .B SIOCGIFNAME Given the .IR ifr_ifindex , return the name of the interface in .IR ifr_name . This is the only ioctl which returns its result in .IR ifr_name . .TP .B SIOCGIFINDEX Retrieve the interface index of the interface into .IR ifr_ifindex . .TP .B SIOCGIFFLAGS .TQ .B SIOCSIFFLAGS Get or set the active flag word of the device. .I ifr_flags contains a bit mask of the following values: .\" Do not right adjust text blocks in tables .na .TS tab(:); c s l l. 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:T{ No arp protocol, L2 destination address not set. T} 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:T{ The addresses are lost when the interface goes down. T} 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) .TE .ad .P Setting the active flag word is a privileged operation, but any process may read it. .TP .B SIOCGIFPFLAGS .TQ .B SIOCSIFPFLAGS Get or set extended (private) flags for the device. .I ifr_flags contains a bit mask of the following values: .TS tab(:); c s l l. 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. .TE .P Setting the extended (private) interface flags is a privileged operation. .TP .B SIOCGIFADDR .TQ .B SIOCSIFADDR .TQ .B SIOCDIFADDR Get, set, or delete the address of the device using .IR ifr_addr , or .I ifr6_addr with .IR ifr6_prefixlen . Setting or deleting the interface address is a privileged operation. For compatibility, .B SIOCGIFADDR returns only .B AF_INET addresses, .B SIOCSIFADDR accepts .B AF_INET and .B AF_INET6 addresses, and .B SIOCDIFADDR deletes only .B AF_INET6 addresses. A .B AF_INET address can be deleted by setting it to zero via .BR SIOCSIFADDR . .TP .B SIOCGIFDSTADDR .TQ .B SIOCSIFDSTADDR Get or set the destination address of a point-to-point device using .IR ifr_dstaddr . For compatibility, only .B AF_INET addresses are accepted or returned. Setting the destination address is a privileged operation. .TP .B SIOCGIFBRDADDR .TQ .B SIOCSIFBRDADDR Get or set the broadcast address for a device using .IR ifr_brdaddr . For compatibility, only .B AF_INET addresses are accepted or returned. Setting the broadcast address is a privileged operation. .TP .B SIOCGIFNETMASK .TQ .B SIOCSIFNETMASK Get or set the network mask for a device using .IR ifr_netmask . For compatibility, only .B AF_INET addresses are accepted or returned. Setting the network mask is a privileged operation. .TP .B SIOCGIFMETRIC .TQ .B SIOCSIFMETRIC Get or set the metric of the device using .IR ifr_metric . This is currently not implemented; it sets .I ifr_metric to 0 if you attempt to read it and returns .B EOPNOTSUPP if you attempt to set it. .TP .B SIOCGIFMTU .TQ .B SIOCSIFMTU Get or set the MTU (Maximum Transfer Unit) of a device using .IR ifr_mtu . Setting the MTU is a privileged operation. Setting the MTU to too small values may cause kernel crashes. .TP .B SIOCGIFHWADDR .TQ .B SIOCSIFHWADDR Get or set the hardware address of a device using .IR ifr_hwaddr . The hardware address is specified in a struct .IR sockaddr . .I sa_family contains the ARPHRD_* device type, .I sa_data the L2 hardware address starting from byte 0. Setting the hardware address is a privileged operation. .TP .B SIOCSIFHWBROADCAST Set the hardware broadcast address of a device from .IR ifr_hwaddr . This is a privileged operation. .TP .B SIOCGIFMAP .TQ .B SIOCSIFMAP Get or set the interface's hardware parameters using .IR ifr_map . Setting the parameters is a privileged operation. .IP .in +4n .EX struct ifmap { unsigned long mem_start; unsigned long mem_end; unsigned short base_addr; unsigned char irq; unsigned char dma; unsigned char port; }; .EE .in .IP The interpretation of the ifmap structure depends on the device driver and the architecture. .TP .B SIOCADDMULTI .TQ .B SIOCDELMULTI Add an address to or delete an address from the device's link layer multicast filters using .IR ifr_hwaddr . These are privileged operations. See also .BR packet (7) for an alternative. .TP .B SIOCGIFTXQLEN .TQ .B SIOCSIFTXQLEN Get or set the transmit queue length of a device using .IR ifr_qlen . Setting the transmit queue length is a privileged operation. .TP .B SIOCSIFNAME Changes the name of the interface specified in .I ifr_name to .IR ifr_newname . This is a privileged operation. It is allowed only when the interface is not up. .TP .B SIOCGIFCONF Return a list of interface (network layer) addresses. This currently means only addresses of the .B AF_INET (IPv4) family for compatibility. Unlike the others, this ioctl passes an .I ifconf structure: .IP .in +4n .EX struct ifconf { int ifc_len; /* size of buffer */ union { char *ifc_buf; /* buffer address */ struct ifreq *ifc_req; /* array of structures */ }; }; .EE .in .IP If .I ifc_req is NULL, .B SIOCGIFCONF returns the necessary buffer size in bytes for receiving all available addresses in .IR ifc_len . Otherwise, .I ifc_req contains a pointer to an array of .I ifreq structures to be filled with all currently active L3 interface addresses. .I ifc_len contains the size of the array in bytes. Within each .I ifreq structure, .I ifr_name will receive the interface name, and .I ifr_addr the address. The actual number of bytes transferred is returned in .IR ifc_len . .IP If the size specified by .I 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 .B SIOCGIFCONF with .I ifc_req set to NULL, or to retry the call with a bigger buffer whenever .I ifc_len upon return differs by less than .I sizeof(struct ifreq) from its original value. .IP If an error occurs accessing the .I ifconf or .I ifreq structures, .B EFAULT will be returned. .\" Slaving isn't supported in Linux 2.2 .\" . .\" .TP .\" .B SIOCGIFSLAVE .\" .TQ .\" .B SIOCSIFSLAVE .\" Get or set the slave device using .\" .IR ifr_slave . .\" Setting the slave device is a privileged operation. .\" .P .\" FIXME . add amateur radio stuff. .P 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 .BR ip (7). .P In addition, some devices support private ioctls. These are not described here. .SH NOTES .B SIOCGIFCONF and the other ioctls that accept or return only .B AF_INET socket addresses are IP-specific and perhaps should rather be documented in .BR ip (7). .P The names of interfaces with no addresses or that don't have the .B IFF_RUNNING flag set can be found via .IR /proc/net/dev . .P .B AF_INET6 IPv6 addresses can be read from .I /proc/net/if_inet6 or via .BR rtnetlink (7). Adding a new IPv6 address and deleting an existing IPv6 address can be done via .B SIOCSIFADDR and .B SIOCDIFADDR or via .BR rtnetlink (7). Retrieving or changing destination IPv6 addresses of a point-to-point interface is possible only via .BR rtnetlink (7). .SH BUGS glibc 2.1 is missing the .I ifr_newname macro in .IR . Add the following to your program as a workaround: .P .in +4n .EX #ifndef ifr_newname #define ifr_newname ifr_ifru.ifru_slave #endif .EE .in .SH SEE ALSO .BR proc (5), .BR capabilities (7), .BR ip (7), .BR rtnetlink (7)