ip - Internet Protocol (IPv4 and IPv6)
#include <sys/socket.h> #include <netinet/in.h>
The following is the socket call for AF_INET sockets:
s = socket(AF_INET, SOCK_RAW, proto);
The following is the socket call for AF_INET6 sockets:
s = socket(AF_INET6, SOCK_RAW, proto);
The Internet Protocol (IP) is the transport layer protocol
used by the Internet Protocol family. Options may be set
at the IP level when using higher-level protocols that are
based on IP (such as the Transmission Control Protocol
(TCP) and the User Datagram Package (UDP)). You can also
access the protocol through a raw socket when developing
new protocols, or special purpose applications. Both IP
version 4 and IP version 6 are supported.
IP-level options are set with the setsockopt() function
and examined with the getsockopt() function. Other options
supported by the getsockopt() and setsockopt() functions
can be found in the <netinet/in.h> header file for IPv4
and in the <netinet/in6.h> header file for IPv6.
Provides IPv4 options to be transmitted in the IPv4 header
of each outgoing packet or examines IPv4 header options on
incoming packets. The format of IPv4 options to be sent
is that specified by the IPv4 specification, with one
exception: the list of addresses for Source Route options
must include the first-hop gateway at the beginning of the
list of gateways. The first-hop gateway address will be
extracted from the option list and the size adjusted
accordingly before use.
IPv4 options may be used with any socket type in
the Internet family. Enables a SOCK_DGRAM socket
to receive the destination IPv4 address for a UDP
datagram. Enables a SOCK_DGRAM socket to receive
the IPv4 options for a UDP datagram. Sets the
type-of-service (TOS) field in the IPv4 header for
a TCP or UDP socket. For example:
int tos; setsockopt(s, IPPROTO_IP, IP_TOS, &tos,
sizeof(tos));
You can set the type-of-service to any of the
defined constants in <netinet/ip.h>. Typically
used constants are: IPTOS_LOWDELAY, IPTOS_THROUGHPUT,
and IPTOS_RELIABILITY.
To determine the current value for this option, use
the getsockopt call. For example:
int tos; getsockopt(s, IPPROTO_IP, IP_TOS, &tos,
sizeof(tos)); Sets the time-to-live (TTL) field in
the IPv4 header for a TCP or UDP socket, by default
the values are 60 and 30, respectively, for example:
int ttl; setsockopt(s, IPPROTO_IP, IP_TTL, &ttl,
sizeof(ttl));
To determine the current value for this option, use
the getsockopt call, for example:
int ttl; getsockopt(s, IPPROTO_IP, IP_TTL, &ttl,
sizeof(ttl)); Enables a SOCK_RAW socket to receive
IPv6 destination options, for example:
int on = 1;
if (setsockopt(s, IPPROTO_IPV6, IPV6_RECVDSTOPTS,
&on, sizeof(on)) == -1)
perror("setsockopt IPV6_RECVDSTOPTS");
Enables a SOCK_RAW socket to receive the
IPv6 hop limit, for example:
int on = 1;
if (setsockopt(s, IPPROTO_IPV6, IPV6_RECVHOPLIMIT,
&on, sizeof(on)) == -1)
perror("setsockopt IPV6_RECVHOPLIMIT");
To determine the current value for this option, use
the getsockopt call. Enables a SOCK_RAW socket to
receive the IPv6 Hop-by-Hop options header, for
example:
int on = 1;
if (setsockopt(s, IPPROTO_IPV6, IPV6_RECVHOPOPTS,
&on, sizeof(on)) == -1)
perror("setsockopt
IPV6_RECVHOPOPTS"); Enables a SOCK_RAW socket to
receive the send and receive interfaces and the
source and destination addresses, for example:
int on = 1;
if (setsockopt(s, IPPROTO_IPV6, IPV6_RECVPKTINFO,
&on, sizeof(on)) == -1)
perror("setsockopt IPV6_RECVPKTINFO");
Enables a SOCK_RAW socket to receive the
IPv6 routing header, for example:
int on = 1;
if (setsockopt(s, IPPROTO_IPV6, IPV6_RECVRTHDR,
&on, sizeof(on)) == -1)
perror("setsockopt
IPV6_RECVRTHDR"); Sets the hop limit for all subsequent
IPv6 unicast packets sent on a specified
socket. For example:
int hoplimit = 10; if (setsockopt(s, IPPROTO_IPV6,
IPV6_UNICAST_HOPS,
(char *) &hoplimit, sizeof(hoplimit))
== -1)
perror("setsockopt
IPV6_UNICAST_HOPS");
To determine the current value for this option, use
the getsockopt call. For example:
int hoplimit; size_t len = sizeof(hoplimit);
if (getsockopt(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS,
(char *) &hoplimit, &len) == -1);
perror("getsockopt IPV6_UNICAST_HOPS"); else
printf("Using %d for hop limit.\n", hoplimit);
Specifies whether to restrict AF_INET6 sockets to
sending and receiving only IPv6 packets. For example:
int on = 1; if (setsockopt(s, IPPROTO_IPV6,
IPV6_V6ONLY,
(char *)&on, sizeof(on)) == -1)
perror("setsockopt IPV6_V6ONLY"); else
printf("IPV6_V6ONLY option set");
If set, operations with IPv4-mapped IPv6 addresses
are not allowed. This is a Boolean option. The
default (0) is to accept both IPv4 and IPv6 packets.
MULTICASTING [Toc] [Back]
IP multicasting is supported on AF_INET and AF_INET6 sockets
of type SOCK_DGRAM and SOCK_RAW only, and only on networks
where the interface driver supports multicasting.
By default, if a multicast datagram is sent to a group to
which the sending host itself belongs (on the outgoing
interface), a copy of the datagram is looped back by the
IP layer for local delivery.
A host must become a member of a multicast group before it
can receive datagrams sent to the group. Memberships in
multicast groups are dropped when the socket is closed or
the process exits.
IPv4 Multicasting [Toc] [Back]
The following IPv4 multicasting options are supported:
Joins an IPv4 multicast group, for example:
struct ip_mreq mreq; setsockopt(s, IPPROTO_IP,
IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));
The mreq parameter is the following structure:
struct ip_mreq {
struct in_addr imr_multiaddr; /* multicast
group to join */
struct in_addr imr_interface; /* interface on
which to join */ }
The imr_interface should be INADDR_ANY to choose
the default multicast interface, or the IPv4
address of a particular multicast-capable interface
if the host is multihomed. Membership is associated
with a single interface; programs running on
multihomed hosts may need to join the same group on
more than one interface. Up to IP_MAX_MEMBERSHIPS
(currently 65535) memberships may be added on a
single socket. Drops a membership in an IPv4 multicast
group, for example:
struct ip_mreq mreq; setsockopt(s, IPPROTO_IP,
IP_DROP_MEMBERSHIP, &mreq, sizeof(mreq));
The mreq parameter contains the same values as used
to add the membership. Overrides the default for
subsequent IPv4 transmissions from a given socket.
By default, for hosts with multiple interfaces,
each multicast transmission is sent from the primary
network interface.
struct in_addr addr; setsockopt(s, IPPROTO_IP,
IP_MULTICAST_IF, &addr, sizeof(addr));
The addr parameter specifies the local IPv4 address
of the desired interface or INADDR_ANY to specify
the default interface. An interface's local IPv4
address and multicast capability can be obtained
through the SIOCGIFCONF and SIOCGIFLAGS ioctls.
Normal applications should not need to use this
option. Specifies whether or not subsequent IPv6
datagrams are looped back, giving the sender
explicit control, for example:
u_char loop; /* 0 = disable, 1 = enable
(default) */ setsockopt(s, IPPROTO_IP, IP_MULTICAST_LOOP,
&loop, sizeof(loop));
This option improves performance for applications
that may have no more than one instance on a single
host (such as a router daemon), by eliminating the
overhead of receiving their own transmissions.
However, applications for which there may be more
than one instance on a single host (such as a conferencing
program) or for which the sender does not
belong to the destination group (such as a timequerying
program) generally should not use this
option.
An IPv4 multicast datagram sent with an initial TTL
greater than 1 may be delivered to the sending host
on a different interface from that on which it was
sent, if the host belongs to the destination group
on that other interface. The loopback control
option has no effect on such delivery. Changes the
time-to-live (TTL) in the header for outgoing IPv4
multicast datagrams in order to control the scope
of the multicasts; for example:
u_char ttl; /* range: 0 to 255, default = 1 */
setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL, &ttl,
sizeof(ttl));
Datagrams with a TTL of 1 are not forwarded beyond
the local network. Multicast datagrams with a TTL
of 0 will not be transmitted on any network, but
may be delivered locally if the sending host
belongs to the destination group and if multicast
loopback has not been disabled on the sending
socket (see the IP_MULTICAST_LOOP option). Multicast
datagrams with TTL greater than 1 may be forwarded
to other networks if a multicast router is
attached to the local network.
IPv6 Multicasting [Toc] [Back]
The following IPv6 multicasting options are supported:
Joins an IPv6 multicast group on the specified interface,
for example:
#include <netinet/in.h>
struct ipv6_mreq imr6;
imr6.ipv6mr_interface = if_index;
if (setsockopt(s, IPPROTO_IPV6, IPV6_JOIN_GROUP,
(char *)&imr6, sizeof(imr6)) < 0) {
perror("setsockopt IPV6_JOIN_GROUP");
}
The ipv6_mreq parameter is the following structure:
struct ipv6_mreq {
struct in6_addr ipv6mr_multiaddr; /* IPv6 multicast
address */
unsigned int ipv6mr_interface; /* interface
index; 0 =>
* pick a default
interface
* that supports IP
multicasts */ };
The ipv6mr_interface should be either zero to
choose the default multicast interface or the
interface index of a particular interface if the
host is multihomed. Membership is associated with
a single interface; programs running on multihomed
hosts may need to join the same group on more than
one interface. Up to IPV6_MAX_MEMBERSHIPS (currently
65536) may be added to a single socket.
IPv4-mapped IPv6 addresses are supported as parameters
for this option. Drops a membership in an
IPv6 multicast group, for example:
#include <netinet/in.h>
struct ipv6_mreq imr6;
if (setsockopt(s, IPPROTO_IPV6, IPV6_LEAVE_GROUP,
(char *)&imr6,
sizeof(imr6)) < 0) {
perror("setsockopt IPV6_LEAVE_GROUP"); }
The imr6 parameter contains the same values as used
to add the membership. IPv4-mapped IPv6 addresses
are supported as valid parameters for this option.
Changes the hop limit for outgoing IPv6 multicast
packets; for example:
int hoplimit = 255; /* range 0 to 255; hop limit =
-1 sets the
* hoplimit to the default value of
1
*/ if (setsockopt(s, IPPROTO_IPV6,
IPV6_MULTICAST_HOPS,
&hoplimit, sizeof(hoplimit)) < 0) {
perror("setsockopt IPV6_MULTICAST_HOPS");
} Sets the interface to use for outgoing
IPv6 multicast packets:
u_int if_index = 1;
if (setsockopt(s, IPPROTO_IPV6, IPV6_MULTICAST_IF,
&if_index, sizeof(ifindex)) < 0)
perror("setsockopt IPV6_MULTICAST_IF");
}
The if_index parameter specifies the interface
index of the desired interface or 0 to select a
default interface. You can use the if_nametoindex()
routine to find the interface index. Specifies
whether or not subsequent IPv6 datagrams are
looped back, for example:
u_int on = 0; /* 0 = disable, 1 = enable; default =
1 */
if (setsockopt(s, IPPROTO_IPV6, IPV6_MULTICAST_LOOP,
&on, sizeof(on)) < 0){
perror("setsockopt
IPV6_MULTICAST_LOOP ");
}
This option improves performance for applications
that may have no more than one instance on a single
host (such as a router daemon), by eliminating the
overhead of receiving their own transmissions.
However, applications for which there may be more
than one instance on a single host (such as a conferencing
program) or for which the sender does not
belong to the destination group (such as a timequerying
program) generally should not use this
option.
An IPv6 multicast datagram sent with an initial hop
limit greater than 1 may be delivered to the sending
host on a different interface from that on
which it was sent, if the host belongs to the destination
group on that other interface. The loopback
control option has no effect on such delivery.
Raw IP Sockets [Toc] [Back]
Raw IP sockets are connectionless, and are normally used
with the sendto() and recvfrom() calls, though the connect()
call may also be used to fix the destination for
future packets, in which case the read() or recv() and
write() or send() functions may be used.
If proto is 0 (zero), the default protocol IPPROTO_RAW is
used for outgoing packets, and only incoming packets destined
for that protocol are received. If proto is nonzero,
that protocol number will be used on outgoing packets and
to filter incoming packets.
For IPv4, outgoing packets automatically have an IP header
prepended to them (based on the destination address and
the protocol number the socket is created with), unless
the IP_HDRINCL option is set. The IP_HDRINCL option specifies
whether the IP header is provided by the sent
packet. Incoming packets are received with IP header and
options intact.
If a socket operation fails, errno may be set to one of
the following values: An attempt was made to create a
socket with a network address for which no network interface
exists. The socket is already connected. This error
occurs when trying to establish connection on a socket or
when trying to send a datagram with the destination
address specified. The system ran out of memory for an
internal data structure. The destination address of a
datagram was not specified, and the socket has not been
connected.
The following errors specific to IP may occur when setting
or getting IP options: An unknown socket option name was
given.
The IP option field was improperly formed; an
option field was shorter than the minimum value or
longer than the option buffer provided.
Functions: getsockopt(2), send(2), recv(2)
Network Information: netintro(7), icmp(7), inet(7), tcp(7)
ip(7)
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