2026-08-04 23:27 @216.73.216.89
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Enhanced by LLM: deepseek-v4-flash / taotoken.net / www.chedong.com - original format
ip - show / manipulate routing, network devices, interfaces and tunnels
| Use Case | Command | Description |
|---|---|---|
| 📋 Show all IP addresses | ip addr | Displays all network interfaces and their IP addresses |
| 📡 Show neighbour table (ARP cache) | ip neigh | Shows the current neighbour table in kernel |
| 🔛 Bring up interface | ip link set x up | Bring up interface x |
| 🔽 Bring down interface | ip link set x down | Bring down interface x |
| 🗺️ Show routing table | ip route | Display the kernel routing table |
| 📦 Execute commands from file | ip -batch filename | Read and execute commands from a file |
| 🌐 Use specific network namespace | ip -n NAME OBJECT | Execute ip command in a specific network namespace |
| 📊 Show statistics | ip -s addr | Show detailed address statistics |
| 📄 JSON output | ip -j addr | Output in JSON format |
ip [ OPTIONS ] OBJECT { COMMAND | help }
ip [ -force ] -batch filename
OBJECT := { link | address | addrlabel | route | rule | neigh | ntable
| tunnel | tuntap | maddress | mroute | mrule | monitor | xfrm
| netns | l2tp | tcp_metrics | token | macsec | vrf | mptcp |
ioam }
OPTIONS := { -V[ersion] | -h[uman-readable] | -s[tatistics] |
-d[etails] | -r[esolve] | -iec | -f[amily] { inet | inet6 |
link } | -4 | -6 | -B | -0 | -l[oops] { maximum-addr-flush-at-
tempts } | -o[neline] | -rc[vbuf] [size] | -t[imestamp] |
-ts[hort] | -n[etns] name | -N[umeric] | -a[ll] | -c[olor] |
-br[ief] | -j[son] | -p[retty] }Print the version of the ip utility and exit.
Output statistics with human readable values followed by suffix.
Read commands from provided file or standard input and invoke them. First failure will cause termination of ip.
Don't terminate ip on errors in batch mode. If there were any errors during execution of the commands, the application return code will be non zero.
Output more information. If the option appears twice or more, the amount of information increases. As a rule, the information is statistics or some time values.
Output more detailed information.
Specify maximum number of loops the 'ip address flush' logic will attempt before giving up. The default is 10. Zero (0) means loop until all addresses are removed.
Specifies the protocol family to use. The protocol family identifier can be one of inet, inet6, bridge, mpls or link. If this option is not present, the protocol family is guessed from other arguments. If the rest of the command line does not give enough information to guess the family, ip falls back to the default one, usually inet or any. link is a special family identifier meaning that no networking protocol is involved.
Shortcut for -family inet.
Shortcut for -family inet6.
Shortcut for -family bridge.
Shortcut for -family mpls.
Shortcut for -family link.
Output each record on a single line, replacing line feeds with the '\' character. This is convenient when you want to count records with wc(1) or to grep(1) the output.
Use the system's name resolver to print DNS names instead of host addresses.
Switches ip to the specified network namespace NETNS. Actually it just simplifies executing of:
ip netns exec NETNS ip [ OPTIONS ] OBJECT { COMMAND | help }to
ip -n[etns] NETNS [ OPTIONS ] OBJECT { COMMAND | help }Print the number of protocol, scope, dsfield, etc directly instead of converting it to human readable name.
Executes specified command over all objects, it depends if command supports this option.
Configure color output. If parameter is omitted or always, color output is enabled regardless of stdout state. If parameter is auto, stdout is checked to be a terminal before enabling color output. If parameter is never, color output is disabled. If specified multiple times, the last one takes precedence. This flag is ignored if -json is also given. Used color palette can be influenced by COLORFGBG environment variable (see ENVIRONMENT).
Display current time when using monitor option.
Like -timestamp, but use shorter format.
Set the netlink socket receive buffer size, defaults to 1MB.
Print human readable rates in IEC units (e.g. 1Ki = 1024).
Print only basic information in a tabular format for better readability. This option is currently only supported by ip addr show , ip link show & ip neigh show commands.
Output results in JavaScript Object Notation (JSON).
The default JSON format is compact and more efficient to parse but hard for most users to read. This flag adds indentation for readability.
address - 📍 protocol (IP or IPv6) address on a device.addrlabel - 🏷️ label configuration for protocol address selection.ioam - 📊 manage IOAM namespaces and IOAM schemas.l2tp - 🚇 tunnel ethernet over IP (L2TPv3).link - 🔗 network device.maddress - 📡 multicast address.monitor - 👁️ watch for netlink messages.mptcp - 🔀 manage MPTCP path manager.mroute - 🗺️ multicast routing cache entry.mrule - 📜 rule in multicast routing policy database.neighbour - 🤝 manage ARP or NDISC cache entries.netns - 🧊 manage network namespaces.ntable - 📋 manage the neighbor cache's operation.route - 🛤️ routing table entry.rule - 📏 rule in routing policy database.tcp_metrics/tcpmetrics - 📊 manage TCP Metricstoken - 🔑 manage tokenized interface identifiers.tunnel - 🚇 tunnel over IP.tuntap - 🎛️ manage TUN/TAP devices.vrf - 🔄 manage virtual routing and forwarding devices.xfrm - 🔒 manage IPSec policies.The names of all objects may be written in full or abbreviated form, for example address can be abbreviated as addr or just a.
Specifies the action to perform on the object. The set of possible actions depends on the object type. As a rule, it is possible to add, delete and show (or list ) objects, but some objects do not allow all of these operations or have some additional commands. The help command is available for all objects. It prints out a list of available commands and argument syntax conventions. If no command is given, some default command is assumed. Usually it is list or, if the objects of this class cannot be listed, help.
If set, it's value is used for detection whether background is dark or light and use contrast colors for it. COLORFGBG environment variable usually contains either two or three values separated by semicolons; we want the last value in either case. If this value is 0-6 or 8, chose colors suitable for dark background:
COLORFGBG=";0" ip -c aip addr - Shows addresses assigned to all network interfaces.ip neigh - Shows the current neighbour table in kernel.ip link set x up - Bring up interface x.ip link set x down - Bring down interface x.ip route - Show table routes.ip was written by Alexey N. Kuznetsov and added in Linux 2.2.
ip-address(8), ip-addrlabel(8), ip-ioam(8), ip-l2tp(8), ip-link(8), maddress(8), ip-monitor(8), ip-mptcp(8), ip-mroute(8), ip-neighbour(8), ip-netns(8), ip-ntable(8), ip-route(8), ip-rule(8), ip-tcp_metrics(8), ip-token(8), ip-tunnel(8), ip-vrf(8), ip-xfrm(8) IP Command reference ip-cref.ps
ip - Linux IPv4 protocol implementation
| Use Case | Socket Option / Setting | Description |
|---|---|---|
| 🔗 Join multicast group | IP_ADD_MEMBERSHIP | Join a multicast group (ip_mreqn structure) |
| 🔗 Leave multicast group | IP_DROP_MEMBERSHIP | Leave a multicast group |
| 📦 Enable PKTINFO | IP_PKTINFO | Pass ancillary message with packet info (interface index, local address, dest address) |
| 🔍 Enable error queue | IP_RECVERR | Enable extended reliable error message passing |
| 📏 Set TTL | IP_TTL | Set time-to-live for outgoing packets |
| 🎯 Set TOS | IP_TOS | Set Type-Of-Service field |
| 🛡️ Transparent proxy | IP_TRANSPARENT | Allow binding to nonlocal IP address (requires CAP_NET_ADMIN) |
| 🔓 Freebind | IP_FREEBIND | Allow binding to nonlocal or nonexistent IP address |
| 📏 Path MTU discovery | IP_MTU_DISCOVER | Set PMTU discovery behavior (WANT, DONT, DO, PROBE) |
| 🔒 Security context | SO_PEERSEC | Get security context of peer socket (labeled IPSEC/NetLabel) |
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h> /* superset of previous */
tcp_socket = socket(AF_INET, SOCK_STREAM, 0);
udp_socket = socket(AF_INET, SOCK_DGRAM, 0);
raw_socket = socket(AF_INET, SOCK_RAW, protocol);Linux implements the Internet Protocol, version 4, described in RFC 791 and RFC 1122. ip contains a level 2 multicasting implementation conforming to RFC 1112. It also contains an IP router including a packet filter. The programming interface is BSD-sockets compatible. For more information on sockets, see socket(7).
An IP socket is created using socket(2):
socket(AF_INET, socket_type, protocol);Valid socket types include SOCK_STREAM to open a stream socket, SOCK_DGRAM to open a datagram socket, and SOCK_RAW to open a raw(7) socket to access the IP protocol directly. protocol is the IP protocol in the IP header to be received or sent. Valid values for protocol include:
For SOCK_RAW you may specify a valid IANA IP protocol defined in RFC 1700 assigned numbers. When a process wants to receive new incoming packets or connections, it should bind a socket to a local interface address using bind(2). In this case, only one IP socket may be bound to any given local (address, port) pair. When INADDR_ANY is specified in the bind call, the socket will be bound to all local interfaces. When listen(2) is called on an unbound socket, the socket is automatically bound to a random free port with the local address set to INADDR_ANY. When connect(2) is called on an unbound socket, the socket is automatically bound to a random free port or to a usable shared port with the local address set to INADDR_ANY. A TCP local socket address that has been bound is unavailable for some time after closing, unless the SO_REUSEADDR flag has been set. Care should be taken when using this flag as it makes TCP less reliable.
An IP socket address is defined as a combination of an IP interface address and a 16-bit port number. The basic IP protocol does not supply port numbers, they are implemented by higher level protocols like udp(7) and tcp(7). On raw sockets sin_port is set to the IP protocol.
struct sockaddr_in {
sa_family_t sin_family; /* address family: AF_INET */
in_port_t sin_port; /* port in network byte order */
struct in_addr sin_addr; /* internet address */
};
/* Internet address. */
struct in_addr {
uint32_t s_addr; /* address in network byte order */
};sin_family is always set to AF_INET. This is required; in Linux 2.2 most networking functions return EINVAL when this setting is missing. sin_port contains the port in network byte order. The port numbers below 1024 are called privileged ports (or sometimes: reserved ports). Only a privileged process (on Linux: a process that has the CAP_NET_BIND_SERVICE capability in the user namespace governing its network namespace) may bind(2) to these sockets. Note that the raw IPv4 protocol as such has no concept of a port, they are implemented only by higher protocols like tcp(7) and udp(7). sin_addr is the IP host address. The s_addr member of struct in_addr contains the host interface address in network byte order. in_addr should be assigned one of the INADDR_* values (e.g., INADDR_LOOPBACK) using htonl(3) or set using the inet_aton(3), inet_addr(3), inet_makeaddr(3) library functions or directly with the name resolver (see gethostbyname(3)). IPv4 addresses are divided into unicast, broadcast, and multicast addresses. Unicast addresses specify a single interface of a host, broadcast addresses specify all hosts on a network, and multicast addresses address all hosts in a multicast group. Datagrams to broadcast addresses can be sent or received only when the SO_BROADCAST socket flag is set. In the current implementation, connection-oriented sockets are allowed to use only unicast addresses. Note that the address and the port are always stored in network byte order. In particular, this means that you need to call htons(3) on the number that is assigned to a port. All address/port manipulation functions in the standard library work in network byte order. There are several special addresses: INADDR_LOOPBACK (127.0.0.1) always refers to the local host via the loopback device; INADDR_ANY (0.0.0.0) means any address for binding; INADDR_BROADCAST (255.255.255.255) means any host and has the same effect on bind as INADDR_ANY for historical reasons.
IP supports some protocol-specific socket options that can be set with setsockopt(2) and read with getsockopt(2). The socket option level for IP is IPPROTO_IP. A boolean integer flag is zero when it is false, otherwise true. When an invalid socket option is specified, getsockopt(2) and setsockopt(2) fail with the error ENOPROTOOPT.
Join a multicast group. Argument is an ip_mreqn structure.
struct ip_mreqn {
struct in_addr imr_multiaddr; /* IP multicast group address */
struct in_addr imr_address; /* IP address of local interface */
int imr_ifindex; /* interface index */
};imr_multiaddr contains the address of the multicast group the application wants to join or leave. It must be a valid multicast address (or setsockopt(2) fails with the error EINVAL). imr_address is the address of the local interface with which the system should join the multicast group; if it is equal to INADDR_ANY, an appropriate interface is chosen by the system. imr_ifindex is the interface index of the interface that should join/leave the imr_multiaddr group, or 0 to indicate any interface. The ip_mreqn structure is available only since Linux 2.2. For compatibility, the old ip_mreq structure (present since Linux 1.2) is still supported; it differs from ip_mreqn only by not including the imr_ifindex field. (The kernel determines which structure is being passed based on the size passed in optlen.) IP_ADD_MEMBERSHIP is valid only for setsockopt(2).
Join a multicast group and allow receiving data only from a specified source. Argument is an ip_mreq_source structure.
struct ip_mreq_source {
struct in_addr imr_multiaddr; /* IP multicast group address */
struct in_addr imr_interface; /* IP address of local interface */
struct in_addr imr_sourceaddr; /* IP address of multicast source */
};This option can be used multiple times to allow receiving data from more than one source.
Inform the kernel to not reserve an ephemeral port when using bind(2) with a port number of 0. The port will later be automatically chosen at connect(2) time, in a way that allows sharing a source port as long as the 4-tuple is unique.
Stop receiving multicast data from a specific source in a given group. This is valid only after the application has subscribed to the multicast group using either IP_ADD_MEMBERSHIP or IP_ADD_SOURCE_MEMBERSHIP. Argument is an ip_mreq_source structure as described under IP_ADD_SOURCE_MEMBERSHIP.
Leave a multicast group. Argument is an ip_mreqn or ip_mreq structure similar to IP_ADD_MEMBERSHIP.
Leave a source-specific group--that is, stop receiving data from a given multicast group that come from a given source. If the application has subscribed to multiple sources within the same group, data from the remaining sources will still be delivered. To stop receiving data from all sources at once, use IP_DROP_MEMBERSHIP. Argument is an ip_mreq_source structure as described under IP_ADD_SOURCE_MEMBERSHIP.
If enabled, this boolean option allows binding to an IP address that is nonlocal or does not (yet) exist. This permits listening on a socket, without requiring the underlying network interface or the specified dynamic IP address to be up at the time that the application is trying to bind to it. This option is the per-socket equivalent of the ip_nonlocal_bind /proc interface described below.
If enabled, the user supplies an IP header in front of the user data. Valid only for SOCK_RAW sockets; see raw(7) for more information. When this flag is enabled, the values set by IP_OPTIONS, IP_TTL, and IP_TOS are ignored.
This option provides access to the advanced full-state filtering API. Argument is an ip_msfilter structure.
struct ip_msfilter {
struct in_addr imsf_multiaddr; /* IP multicast group address */
struct in_addr imsf_interface; /* IP address of local interface */
uint32_t imsf_fmode; /* Filter-mode */
uint32_t imsf_numsrc; /* Number of sources in the following array */
struct in_addr imsf_slist[1]; /* Array of source addresses */
};There are two macros, MCAST_INCLUDE and MCAST_EXCLUDE, which can be used to specify the filtering mode. Additionally, the IP_MSFILTER_SIZE(n) macro exists to determine how much memory is needed to store ip_msfilter structure with n sources in the source list. For the full description of multicast source filtering refer to RFC 3376.
Retrieve the current known path MTU of the current socket. Returns an integer. IP_MTU is valid only for getsockopt(2) and can be employed only when the socket has been connected.
Set or receive the Path MTU Discovery setting for a socket. When enabled, Linux will perform Path MTU Discovery as defined in RFC 1191 on SOCK_STREAM sockets. For non-SOCK_STREAM sockets, IP_PMTUDISC_DO forces the don't-fragment flag to be set on all outgoing packets. It is the user's responsibility to packetize the data in MTU-sized chunks and to do the retransmits if necessary. The kernel will reject (with EMSGSIZE) datagrams that are bigger than the known path MTU. IP_PMTUDISC_WANT will fragment a datagram if needed according to the path MTU, or will set the don't-fragment flag otherwise. The system-wide default can be toggled between IP_PMTUDISC_WANT and IP_PMTUDISC_DONT by writing (respectively, zero and nonzero values) to the /proc/sys/net/ipv4/ip_no_pmtu_disc file.
This option can be used to modify the delivery policy of multicast messages to sockets bound to the wildcard INADDR_ANY address. The argument is a boolean integer (defaults to 1). If set to 1, the socket will receive messages from all the groups that have been joined globally on the whole system. Otherwise, it will deliver messages only from the groups that have been explicitly joined (for example via the IP_ADD_MEMBERSHIP option) on this particular socket.
Set the local device for a multicast socket. The argument for setsockopt(2) is an ip_mreqn or (since Linux 3.5) ip_mreq structure similar to IP_ADD_MEMBERSHIP, or an in_addr structure. (The kernel determines which structure is being passed based on the size passed in optlen.) For getsockopt(2), the argument is an in_addr structure.
Set or read a boolean integer argument that determines whether sent multicast packets should be looped back to the local sockets.
Set or read the time-to-live value of outgoing multicast packets for this socket. It is very important for multicast packets to set the smallest TTL possible. The default is 1 which means that multicast packets don't leave the local network unless the user program explicitly requests it. Argument is an integer.
If enabled (argument is nonzero), the reassembly of outgoing packets is disabled in the netfilter layer. The argument is an integer. This option is valid only for SOCK_RAW sockets.
Set or get the IP options to be sent with every packet from this socket. The arguments are a pointer to a memory buffer containing the options and the option length. The setsockopt(2) call sets the IP options associated with a socket. The maximum option size for IPv4 is 40 bytes. See RFC 791 for the allowed options. When the initial connection request packet for a SOCK_STREAM socket contains IP options, the IP options will be set automatically to the options from the initial packet with routing headers reversed. Incoming packets are not allowed to change options after the connection is established. The processing of all incoming source routing options is disabled by default and can be enabled by using the accept_source_route /proc interface. Other options like timestamps are still handled. For datagram sockets, IP options can be set only by the local user. Calling getsockopt(2) with IP_OPTIONS puts the current IP options used for sending into the supplied buffer.
If labeled IPSEC or NetLabel is configured on the sending and receiving hosts, this option enables receiving of the security context of the peer socket in an ancillary message of type SCM_SECURITY retrieved using recvmsg(2). This option is supported only for UDP sockets; for TCP or SCTP sockets, see the description of the SO_PEERSEC option below. The value given as an argument to setsockopt(2) and returned as the result of getsockopt(2) is an integer boolean flag. The security context returned in the SCM_SECURITY ancillary message is of the same format as the one described under the SO_PEERSEC option below. Note: the reuse of the SCM_SECURITY message type for the IP_PASSSEC socket option was likely a mistake, since other IP control messages use their own numbering scheme in the IP namespace and often use the socket option value as the message type. There is no conflict currently since the IP option with the same value as SCM_SECURITY is IP_HDRINCL and this is never used for a control message type.
Pass an IP_PKTINFO ancillary message that contains a pktinfo structure that supplies some information about the incoming packet. This works only for datagram oriented sockets. The argument is a flag that tells the socket whether the IP_PKTINFO message should be passed or not. The message itself can be sent/retrieved only as a control message with a packet using recvmsg(2) or sendmsg(2).
struct in_pktinfo {
unsigned int ipi_ifindex; /* Interface index */
struct in_addr ipi_spec_dst; /* Local address */
struct in_addr ipi_addr; /* Header Destination address */
};ipi_ifindex is the unique index of the interface the packet was received on. ipi_spec_dst is the local address of the packet and ipi_addr is the destination address in the packet header. If IP_PKTINFO is passed to sendmsg(2) and ipi_spec_dst is not zero, then it is used as the local source address for the routing table lookup and for setting up IP source route options. When ipi_ifindex is not zero, the primary local address of the interface specified by the index overwrites ipi_spec_dst for the routing table lookup.
Enable extended reliable error message passing. When enabled on a datagram socket, all generated errors will be queued in a per-socket error queue. When the user receives an error from a socket operation, the errors can be received by calling recvmsg(2) with the MSG_ERRQUEUE flag set. The sock_extended_err structure describing the error will be passed in an ancillary message with the type IP_RECVERR and the level IPPROTO_IP. This is useful for reliable error handling on unconnected sockets. The received data portion of the error queue contains the error packet. The IP_RECVERR control message contains a sock_extended_err structure:
#define SO_EE_ORIGIN_NONE 0
#define SO_EE_ORIGIN_LOCAL 1
#define SO_EE_ORIGIN_ICMP 2
#define SO_EE_ORIGIN_ICMP6 3
struct sock_extended_err {
uint32_t ee_errno; /* error number */
uint8_t ee_origin; /* where the error originated */
uint8_t ee_type; /* type */
uint8_t ee_code; /* code */
uint8_t ee_pad;
uint32_t ee_info; /* additional information */
uint32_t ee_data; /* other data */
/* More data may follow */
};
struct sockaddr *SO_EE_OFFENDER(struct sock_extended_err *);ee_errno contains the errno number of the queued error. ee_origin is the origin code of where the error originated. The other fields are protocol-specific. The macro SO_EE_OFFENDER returns a pointer to the address of the network object where the error originated from given a pointer to the ancillary message. If this address is not known, the sa_family member of the sockaddr contains AF_UNSPEC and the other fields of the sockaddr are undefined. IP uses the sock_extended_err structure as follows: ee_origin is set to SO_EE_ORIGIN_ICMP for errors received as an ICMP packet, or SO_EE_ORIGIN_LOCAL for locally generated errors. Unknown values should be ignored. ee_type and ee_code are set from the type and code fields of the ICMP header. ee_info contains the discovered MTU for EMSGSIZE errors. The message also contains the sockaddr_in of the node caused the error, which can be accessed with the SO_EE_OFFENDER macro. The sin_family field of the SO_EE_OFFENDER address is AF_UNSPEC when the source was unknown. When the error originated from the network, all IP options (IP_OPTIONS, IP_TTL, etc.) enabled on the socket and contained in the error packet are passed as control messages. The payload of the packet causing the error is returned as normal payload. Note that TCP has no error queue; MSG_ERRQUEUE is not permitted on SOCK_STREAM sockets. IP_RECVERR is valid for TCP, but all errors are returned by socket function return or SO_ERROR only. For raw sockets, IP_RECVERR enables passing of all received ICMP errors to the application, otherwise errors are reported only on connected sockets. It sets or retrieves an integer boolean flag. IP_RECVERR defaults to off.
Pass all incoming IP options to the user in a IP_OPTIONS control message. The routing header and other options are already filled in for the local host. Not supported for SOCK_STREAM sockets.
This boolean option enables the IP_ORIGDSTADDR ancillary message in recvmsg(2), in which the kernel returns the original destination address of the datagram being received. The ancillary message contains a struct sockaddr_in.
If enabled, the IP_TOS ancillary message is passed with incoming packets. It contains a byte which specifies the Type of Service/Precedence field of the packet header. Expects a boolean integer flag.
When this flag is set, pass a IP_TTL control message with the time-to-live field of the received packet as a 32 bit integer. Not supported for SOCK_STREAM sockets.
Identical to IP_RECVOPTS, but returns raw unprocessed options with timestamp and route record options not filled in for this hop.
Pass all to-be forwarded packets with the IP Router Alert option set to this socket. Valid only for raw sockets. This is useful, for instance, for user-space RSVP daemons. The tapped packets are not forwarded by the kernel; it is the user's responsibility to send them out again. Socket binding is ignored, such packets are filtered only by protocol. Expects an integer flag.
Set or receive the Type-Of-Service (TOS) field that is sent with every IP packet originating from this socket. It is used to prioritize packets on the network. TOS is a byte. There are some standard TOS flags defined: IPTOS_LOWDELAY to minimize delays for interactive traffic, IPTOS_THROUGHPUT to optimize throughput, IPTOS_RELIABILITY to optimize for reliability, IPTOS_MINCOST should be used for "filler data" where slow transmission doesn't matter. At most one of these TOS values can be specified. Other bits are invalid and shall be cleared. Linux sends IPTOS_LOWDELAY datagrams first by default, but the exact behavior depends on the configured queueing discipline. Some high-priority levels may require superuser privileges (the CAP_NET_ADMIN capability).
Setting this boolean option enables transparent proxying on this socket. This socket option allows the calling application to bind to a nonlocal IP address and operate both as a client and a server with the foreign address as the local endpoint. NOTE: this requires that routing be set up in a way that packets going to the foreign address are routed through the TProxy box (i.e., the system hosting the application that employs the IP_TRANSPARENT socket option). Enabling this socket option requires superuser privileges (the CAP_NET_ADMIN capability). TProxy redirection with the iptables TPROXY target also requires that this option be set on the redirected socket.
Set or retrieve the current time-to-live field that is used in every packet sent from this socket.
Unblock previously blocked multicast source. Returns EADDRNOTAVAIL when given source is not being blocked. Argument is an ip_mreq_source structure as described under IP_ADD_SOURCE_MEMBERSHIP.
If labeled IPSEC or NetLabel is configured on both the sending and receiving hosts, this read-only socket option returns the security context of the peer socket connected to this socket. By default, this will be the same as the security context of the process that created the peer socket unless overridden by the policy or by a process with the required permissions. The argument to getsockopt(2) is a pointer to a buffer of the specified length in bytes into which the security context string will be copied. If the buffer length is less than the length of the security context string, then getsockopt(2) returns -1, sets errno to ERANGE, and returns the required length via optlen. The caller should allocate at least NAME_MAX bytes for the buffer initially, although this is not guaranteed to be sufficient. Resizing the buffer to the returned length and retrying may be necessary. The security context string may include a terminating null character in the returned length, but is not guaranteed to do so: a security context "foo" might be represented as either {'f','o','o'} of length 3 or {'f','o','o','\0'} of length 4, which are considered to be interchangeable. The string is printable, does not contain non-terminating null characters, and is in an unspecified encoding (in particular, it is not guaranteed to be ASCII or UTF-8). The use of this option for sockets in the AF_INET address family is supported since Linux 2.6.17 for TCP sockets, and since Linux 4.17 for SCTP sockets. For SELinux, NetLabel conveys only the MLS portion of the security context of the peer across the wire, defaulting the rest of the security context to the values defined in the policy for the netmsg initial security identifier (SID). However, NetLabel can be configured to pass full security contexts over loopback. Labeled IPSEC always passes full security contexts as part of establishing the security association (SA) and looks them up based on the association for each packet.
The IP protocol supports a set of /proc interfaces to configure some global parameters. The parameters can be accessed by reading or writing files in the directory /proc/sys/net/ipv4/. Interfaces described as Boolean take an integer value, with a nonzero value ("true") meaning that the corresponding option is enabled, and a zero value ("false") meaning that the option is disabled.
All ioctls described in socket(7) apply to ip. Ioctls to configure generic device parameters are described in netdevice(7).
Other errors may be generated by the overlaying protocols; see tcp(7), raw(7), udp(7), and socket(7).
IP_FREEBIND, IP_MSFILTER, IP_MTU, IP_MTU_DISCOVER, IP_RECVORIGDSTADDR, IP_PASSSEC, IP_PKTINFO, IP_RECVERR, IP_ROUTER_ALERT, and IP_TRANSPARENT are Linux-specific. Be very careful with the SO_BROADCAST option - it is not privileged in Linux. It is easy to overload the network with careless broadcasts. For new application protocols it is better to use a multicast group instead of broadcasting. Broadcasting is discouraged. Some other BSD sockets implementations provide IP_RCVDSTADDR and IP_RECVIF socket options to get the destination address and the interface of received datagrams. Linux has the more general IP_PKTINFO for the same task. Some BSD sockets implementations also provide an IP_RECVTTL option, but an ancillary message with type IP_RECVTTL is passed with the incoming packet. This is different from the IP_TTL option used in Linux. Using the SOL_IP socket options level isn't portable; BSD-based stacks use the IPPROTO_IP level. INADDR_ANY (0.0.0.0) and INADDR_BROADCAST (255.255.255.255) are byte-order-neutral. This means htonl(3) has no effect on them.
For compatibility with Linux 2.0, the obsolete socket(AF_INET, SOCK_PACKET, protocol) syntax is still supported to open a packet(7) socket. This is deprecated and should be replaced by socket(AF_PACKET, SOCK_RAW, protocol) instead. The main difference is the new sockaddr_ll address structure for generic link layer information instead of the old sockaddr_pkt.
There are too many inconsistent error values. The error used to diagnose exhaustion of the ephemeral port range differs across the various system calls (connect(2), bind(2), listen(2), sendto(2)) that can assign ephemeral ports. The ioctls to configure IP-specific interface options and ARP tables are not described. Receiving the original destination address with MSG_ERRQUEUE in msg_name by recvmsg(2) does not work in some 2.2 kernels.
recvmsg(2), sendmsg(2), byteorder(3), capabilities(7), icmp(7), ipv6(7), netdevice(7), netlink(7), raw(7), socket(7), tcp(7), udp(7), ip(8) The kernel source file Documentation/networking/ip-sysctl.txt. RFC 791 for the original IP specification. RFC 1122 for the IPv4 host requirements. RFC 1812 for the IPv4 router requirements.
This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
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