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.
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.
- 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 (headers up to 64 kilobytes
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 32 bit integer. 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.
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).
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.
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),
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.