|
NAME | SYNOPSIS | DESCRIPTION | ERRORS | NOTES | BUGS | SEE ALSO | COLOPHON |
IP(7) Linux Programmer's Manual IP(7)
ip - Linux IPv4 protocol implementation
#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 are SOCK_STREAM to open a tcp(7) socket,
SOCK_DGRAM to open a udp(7) socket, or 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. The only valid
values for protocol are 0 and IPPROTO_TCP for TCP sockets, and 0 and
IPPROTO_UDP for UDP sockets. 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.
Address format
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_ANY) 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.
Socket options
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.
IP_ADD_MEMBERSHIP (since Linux 1.2)
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).
IP_ADD_SOURCE_MEMBERSHIP (since Linux 2.4.22 / 2.5.68)
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 */
};
The ip_mreq_source structure is similar to ip_mreqn described
under IP_ADD_MEMBERSIP. The imr_multiaddr field contains the
address of the multicast group the application wants to join
or leave. The imr_interface field is the address of the local
interface with which the system should join the multicast
group. Finally, the imr_sourceaddr field contains the address
of the source the application wants to receive data from.
This option can be used multiple times to allow receiving data
from more than one source.
IP_BIND_ADDRESS_NO_PORT (since Linux 4.2)
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.
IP_BLOCK_SOURCE (since Linux 2.4.22 / 2.5.68)
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.
IP_DROP_MEMBERSHIP (since Linux 1.2)
Leave a multicast group. Argument is an ip_mreqn or ip_mreq
structure similar to IP_ADD_MEMBERSHIP.
IP_DROP_SOURCE_MEMBERSHIP (since Linux 2.4.22 / 2.5.68)
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.
IP_FREEBIND (since Linux 2.4)
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.
IP_HDRINCL (since Linux 2.0)
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.
IP_MSFILTER (since Linux 2.4.22 / 2.5.68)
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.
IP_MTU (since Linux 2.2)
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.
IP_MTU_DISCOVER (since Linux 2.2)
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.
Path MTU discovery value Meaning
IP_PMTUDISC_WANT Use per-route settings.
IP_PMTUDISC_DONT Never do Path MTU Discovery.
IP_PMTUDISC_DO Always do Path MTU Discovery.
IP_PMTUDISC_PROBE Set DF but ignore Path MTU.
When PMTU discovery is enabled, the kernel automatically keeps
track of the path MTU per destination host. When it is
connected to a specific peer with connect(2), the currently
known path MTU can be retrieved conveniently using the IP_MTU
socket option (e.g., after an EMSGSIZE error occurred). The
path MTU may change over time. For connectionless sockets
with many destinations, the new MTU for a given destination
can also be accessed using the error queue (see IP_RECVERR).
A new error will be queued for every incoming MTU update.
While MTU discovery is in progress, initial packets from
datagram sockets may be dropped. Applications using UDP
should be aware of this and not take it into account for their
packet retransmit strategy.
To bootstrap the path MTU discovery process on unconnected
sockets, it is possible to start with a big datagram size (up
to 64K-headers bytes long) and let it shrink by updates of the
path MTU.
To get an initial estimate of the path MTU, connect a datagram
socket to the destination address using connect(2) and
retrieve the MTU by calling getsockopt(2) with the IP_MTU
option.
It is possible to implement RFC 4821 MTU probing with
SOCK_DGRAM or SOCK_RAW sockets by setting a value of
IP_PMTUDISC_PROBE (available since Linux 2.6.22). This is
also particularly useful for diagnostic tools such as
tracepath(8) that wish to deliberately send probe packets
larger than the observed Path MTU.
IP_MULTICAST_ALL (since Linux 2.6.31)
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.
IP_MULTICAST_IF (since Linux 1.2)
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.
IP_MULTICAST_LOOP (since Linux 1.2)
Set or read a boolean integer argument that determines whether
sent multicast packets should be looped back to the local
sockets.
IP_MULTICAST_TTL (since Linux 1.2)
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.
IP_NODEFRAG (since Linux 2.6.36)
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.
IP_OPTIONS (since Linux 2.0)
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 only set by the local user. Calling
getsockopt(2) with IP_OPTIONS puts the current IP options used
for sending into the supplied buffer.
IP_PKTINFO (since Linux 2.2)
Pass an IP_PKTINFO ancillary message that contains a pktinfo
structure that supplies some information about the incoming
packet. This only works 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 only be sent/retrieved as 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.
IP_RECVERR (since Linux 2.2)
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 only
reported on connected sockets
It sets or retrieves an integer boolean flag. IP_RECVERR
defaults to off.
IP_RECVOPTS (since Linux 2.2)
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.
IP_RECVORIGDSTADDR (since Linux 2.6.29)
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.
IP_RECVTOS (since Linux 2.2)
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.
IP_RECVTTL (since Linux 2.2)
When this flag is set, pass a IP_TTL control message with the
time-to-live field of the received packet as a byte. Not
supported for SOCK_STREAM sockets.
IP_RETOPTS (since Linux 2.2)
Identical to IP_RECVOPTS, but returns raw unprocessed options
with timestamp and route record options not filled in for this
hop.
IP_ROUTER_ALERT (since Linux 2.2)
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 only filtered by protocol.
Expects an integer flag.
IP_TOS (since Linux 1.0)
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).
IP_TRANSPARENT (since Linux 2.6.24)
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.
IP_TTL (since Linux 1.0)
Set or retrieve the current time-to-live field that is used in
every packet sent from this socket.
IP_UNBLOCK_SOURCE (since Linux 2.4.22 / 2.5.68)
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.
/proc interfaces
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.
ip_always_defrag (Boolean; since Linux 2.2.13)
[New with kernel 2.2.13; in earlier kernel versions this
feature was controlled at compile time by the
CONFIG_IP_ALWAYS_DEFRAG option; this option is not present in
2.4.x and later]
When this boolean flag is enabled (not equal 0), incoming
fragments (parts of IP packets that arose when some host
between origin and destination decided that the packets were
too large and cut them into pieces) will be reassembled
(defragmented) before being processed, even if they are about
to be forwarded.
Enable only if running either a firewall that is the sole link
to your network or a transparent proxy; never ever use it for
a normal router or host. Otherwise, fragmented communication
can be disturbed if the fragments travel over different links.
Defragmentation also has a large memory and CPU time cost.
This is automagically turned on when masquerading or
transparent proxying are configured.
ip_autoconfig (since Linux 2.2 to 2.6.17)
Not documented.
ip_default_ttl (integer; default: 64; since Linux 2.2)
Set the default time-to-live value of outgoing packets. This
can be changed per socket with the IP_TTL option.
ip_dynaddr (Boolean; default: disabled; since Linux 2.0.31)
Enable dynamic socket address and masquerading entry rewriting
on interface address change. This is useful for dialup
interface with changing IP addresses. 0 means no rewriting, 1
turns it on and 2 enables verbose mode.
ip_forward (Boolean; default: disabled; since Linux 1.2)
Enable IP forwarding with a boolean flag. IP forwarding can
be also set on a per-interface basis.
ip_local_port_range (since Linux 2.2)
This file contains two integers that define the default local
port range allocated to sockets that are not explicitly bound
to a port number—that is, the range used for ephemeral ports.
An ephemeral port is allocated to a socket in the following
circumstances:
* the port number in a socket address is specified as 0 when
calling bind(2);
* listen(2) is called on a stream socket that was not
previously bound;
* connect(2) was called on a socket that was not previously
bound;
* sendto(2) is called on a datagram socket that was not
previously bound.
Allocation of ephemeral ports starts with the first number in
ip_local_port_range and ends with the second number. If the
range of ephemeral ports is exhausted, then the relevant
system call returns an error (but see BUGS).
Note that the port range in ip_local_port_range should not
conflict with the ports used by masquerading (although the
case is handled). Also, arbitrary choices may cause problems
with some firewall packet filters that make assumptions about
the local ports in use. The first number should be at least
greater than 1024, or better, greater than 4096, to avoid
clashes with well known ports and to minimize firewall
problems.
ip_no_pmtu_disc (Boolean; default: disabled; since Linux 2.2)
If enabled, don't do Path MTU Discovery for TCP sockets by
default. Path MTU discovery may fail if misconfigured
firewalls (that drop all ICMP packets) or misconfigured
interfaces (e.g., a point-to-point link where the both ends
don't agree on the MTU) are on the path. It is better to fix
the broken routers on the path than to turn off Path MTU
Discovery globally, because not doing it incurs a high cost to
the network.
ip_nonlocal_bind (Boolean; default: disabled; since Linux 2.4)
If set, allows processes to bind(2) to nonlocal IP addresses,
which can be quite useful, but may break some applications.
ip6frag_time (integer; default: 30)
Time in seconds to keep an IPv6 fragment in memory.
ip6frag_secret_interval (integer; default: 600)
Regeneration interval (in seconds) of the hash secret (or
lifetime for the hash secret) for IPv6 fragments.
ipfrag_high_thresh (integer), ipfrag_low_thresh (integer)
If the amount of queued IP fragments reaches
ipfrag_high_thresh, the queue is pruned down to
ipfrag_low_thresh. Contains an integer with the number of
bytes.
neigh/*
See arp(7).
Ioctls
All ioctls described in socket(7) apply to ip.
Ioctls to configure generic device parameters are described in
netdevice(7).
EACCES The user tried to execute an operation without the necessary
permissions. These include: sending a packet to a broadcast
address without having the SO_BROADCAST flag set; sending a
packet via a prohibit route; modifying firewall settings
without superuser privileges (the CAP_NET_ADMIN capability);
binding to a privileged port without superuser privileges (the
CAP_NET_BIND_SERVICE capability).
EADDRINUSE
Tried to bind to an address already in use.
EADDRNOTAVAIL
A nonexistent interface was requested or the requested source
address was not local.
EAGAIN Operation on a nonblocking socket would block.
EALREADY
A connection operation on a nonblocking socket is already in
progress.
ECONNABORTED
A connection was closed during an accept(2).
EHOSTUNREACH
No valid routing table entry matches the destination address.
This error can be caused by an ICMP message from a remote
router or for the local routing table.
EINVAL Invalid argument passed. For send operations this can be
caused by sending to a blackhole route.
EISCONN
connect(2) was called on an already connected socket.
EMSGSIZE
Datagram is bigger than an MTU on the path and it cannot be
fragmented.
ENOBUFS, ENOMEM
Not enough free memory. This often means that the memory
allocation is limited by the socket buffer limits, not by the
system memory, but this is not 100% consistent.
ENOENT SIOCGSTAMP was called on a socket where no packet arrived.
ENOPKG A kernel subsystem was not configured.
ENOPROTOOPT and EOPNOTSUPP
Invalid socket option passed.
ENOTCONN
The operation is defined only on a connected socket, but the
socket wasn't connected.
EPERM User doesn't have permission to set high priority, change
configuration, or send signals to the requested process or
group.
EPIPE The connection was unexpectedly closed or shut down by the
other end.
ESOCKTNOSUPPORT
The socket is not configured or an unknown socket type was
requested.
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_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.
Compatibility
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), ipfw(4), capabilities(7),
icmp(7), ipv6(7), netlink(7), raw(7), socket(7), tcp(7), udp(7),
ip(8)
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 4.12 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/.
Linux 2017-03-13 IP(7)
Pages that refer to this page: bind(2), connect(2), getpeername(2), getsockname(2), getsockopt(2), listen(2), recv(2), send(2), socket(2), getaddrinfo(3), getaddrinfo_a(3), sctp_connectx(3), sd_is_fifo(3), proc(5), systemd.socket(5), arp(7), icmp(7), ipv6(7), netdevice(7), packet(7), raw(7), rtnetlink(7), sctp(7), socket(7), tcp(7), udp(7), udplite(7)