SunOS man pages : ip (7)
Protocols ip(7P)
NAME
ip, IP - Internet Protocol
SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>
s = socket(AF_INET, SOCK_RAW, proto);
t = t_open ("/dev/rawip", O_RDWR);
DESCRIPTION
IP is the internetwork datagram delivery protocol that is
central to the Internet protocol family. Programs may use IP
through higher-level protocols such as the Transmission Con-
trol Protocol (TCP) or the User Datagram Protocol (UDP), or
may interface directly to IP. See tcp(7P) and udp(7P).
Direct access may be by means of the socket interface, using
a "raw socket," or by means of the Transport Level Interface
("TLI"). The protocol options defined in the IP specifica-
tion may be set in outgoing datagrams.
APPLICATION PROGRAMMING INTERFACE
The STREAMS driver /dev/rawip is the TLI transport provider
that provides raw access to IP.
Raw IP sockets are connectionless and are normally used with
the sendto() and recvfrom() calls (see send(3SOCKET) and
recv(3SOCKET)), although the connect(3SOCKET) call may also
be used to fix the destination for future datagram. In this
case, the read(2) or recv(3SOCKET) and write(2) or
send(3SOCKET) calls may be used. If proto is IPPROTO_RAW or
IPPROTO_IGMP, the application is expected to include a com-
plete IP header when sending. Otherwise, that protocol
number will be set in outgoing datagrams and used to filter
incoming datagrams and an IP header will be generated and
prepended to each outgoing datagram. In either case,
received datagrams are returned with the IP header and
options intact.
The socket options supported at the IP level are:
IP_OPTIONS
IP options for outgoing datagrams. This socket
option may be used to set IP options to be
included in each outgoing datagram. IP options to
be sent are set with setsockopt() (see
getsockopt(3SOCKET)). The getsockopt(3SOCKET)
call returns the IP options set in the last set-
sockopt() call. IP options on received datagrams
are visible to user programs only using raw IP
SunOS 5.8 Last change: 23 Feb 2000 1
Protocols ip(7P)
sockets. The format of IP options given in set-
sockopt() matches those defined in the IP specif-
ication with one exception: the list of addresses
for the source routing 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. IP options may
be used with any socket type in the Internet fam-
ily.
IP_SEC_OPT
Enable or obtain IPsec security settings for this
socket. For more details on the protection ser-
vices of IPsec, see ipsec(7P).
IP_ADD_MEMBERSHIP
Join a multicast group.
IP_DROP_MEMBERSHIP
Leave a multicast group.
These options take a struct ip_mreq as the parameter. The
structure contains a multicast address which has to be set
to the CLASS-D IP multicast address, and an interface
address. Normally the interface address is set to INADDR_ANY
which causes the kernel to choose the interface to join on.
IP_MULTICAST_IF
The outgoing interface for multicast packets.
This option takes a struct in_addr as an argu-
ment, and it selects that interface for outgoing
IP multicast packets. If the address specified is
INADDR_ANY, it will use the unicast routing table
to select the outgoing interface (which is the
default behavior).
IP_MULTICAST_TTL
Time to live for multicast datagrams. This option
takes an unsigned character as an argument. Its
value is the TTL that IP will use on outgoing
multicast datagrams. The default is 1.
IP_MULTICAST_LOOP
Loopback for multicast datagrams. Normally multi-
cast datagrams are delivered to members on the
sending host. Setting the unsigned character
argument to 0 will cause the opposite behavior.
IP_TOS
This option takes an integer argument as its
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Protocols ip(7P)
input value. The least significant 8 bits of the
value are used to set the Type Of Service field
in the IP header of the outgoing packets.
The multicast socket options can be used with any datagram
socket type in the Internet family.
At the socket level, the socket option SO_DONTROUTE may be
applied. This option forces datagrams being sent to bypass
routing and forwarding by forcing the IP Time To Live field
to 1, meaning that the packet will not be forwarded by
routers.
Raw IP datagrams can also be sent and received using the
TLI connectionless primitives.
Datagrams flow through the IP layer in two directions: from
the network up to user processes and from user processes
down to the network. Using this orientation, IP is layered
above the network interface drivers and below the transport
protocols such as UDP and TCP. The Internet Control Message
Protocol (ICMP) is logically a part of IP. See icmp(7P).
IP provides for a checksum of the header part, but not the
data part, of the datagram. The checksum value is computed
and set in the process of sending datagrams and checked when
receiving datagrams.
IP options in received datagrams are processed in the IP
layer according to the protocol specification. Currently
recognized IP options include: security, loose source and
record route (LSRR), strict source and record route (SSRR),
record route, and internet timestamp.
The IP layer will normally act as a router (forwarding
datagrams that are not addressed to it, among other things)
when the machine has two or more interfaces that are up.
This behavior can be overridden by using
ndd(1M) to set the /dev/ip variable, ip_forwarding. The
value 0 means do not forward; the value 1 means forward. The
initialization scripts (see /etc/init.d/inetinit) set this
value at boot time based on the number of "up" interfaces,
but will not turn on IP forwarding at all if the file
/etc/notrouter exists. When the IP module is loaded,
ip_forwarding is 0 and remains so if:
o only one non-DHCP-managed interface is up (the most
common case)
o the file /etc/notrouter exists and DHCP does not say
that IP forwarding is on
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Protocols ip(7P)
o the file /etc/defaultrouter exists and DHCP does not
say IP forwarding is onOtherwise, ip_forwarding will
be set to 1.
Additionally, finer-grained forwarding can be configured in
IP. Each interface will create an <ifname>:ip_forwarding
/dev/ip variable that can be modified using ndd(1M). If a
per-interface :ip_forwarding variable is set to 0, packets
will neither be forwarded from this interface to others, nor
forwarded to this interface.
Setting the ip_forwarding variable will toggle all of the
per-interface :ip_forwarding variables to the setting of
ip_forwarding.
The IP layer will send an ICMP message back to the source
host in many cases when it receives a datagram that can not
be handled. A "time exceeded" ICMP message will be sent if
the "time to live" field in the IP header drops to zero in
the process of forwarding a datagram. A "destination
unreachable" message will be sent if a datagram can not be
forwarded because there is no route to the final destina-
tion, or if it can not be fragmented. If the datagram is
addressed to the local host but is destined for a protocol
that is not supported or a port that is not in use, a desti-
nation unreachable message will also be sent. The IP layer
may send an ICMP "source quench" message if it is receiving
datagrams too quickly. ICMP messages are only sent for the
first fragment of a fragmented datagram and are never
returned in response to errors in other ICMP messages.
The IP layer supports fragmentation and reassembly.
Datagrams are fragmented on output if the datagram is larger
than the maximum transmission unit (MTU) of the network
interface. Fragments of received datagrams are dropped from
the reassembly queues if the complete datagram is not recon-
structed within a short time period.
Errors in sending discovered at the network interface driver
layer are passed by IP back up to the user process.
SEE ALSO
ndd(1M), read(2), write(2), bind(3SOCKET), connect(3SOCKET),
getsockopt(3SOCKET), recv(3SOCKET), send(3SOCKET), defaultrouter(4)
, icmp(7P), if_tcp(7P), inet(7P), ip6(7P),
ipsec(7P), routing(7P), tcp(7P), udp(7P)
Braden, R., RFC 1122, Requirements for Internet Hosts - Com-
munication Layers, Information Sciences Institute, Univer-
sity of Southern California, October 1989.
Postel, J., RFC 791, Internet Protocol - DARPA Internet Pro-
gram Protocol Specification, Information Sciences
SunOS 5.8 Last change: 23 Feb 2000 4
Protocols ip(7P)
Institute, University of Southern California, September
1981.
DIAGNOSTICS
A socket operation may fail with one of the following errors
returned:
EACCES
A bind() operation was attempted with a "reserved"
port number and the effective user ID of the process
was not the privileged user.
EADDRINUSE
A bind() operation was attempted on a socket with a
network address/port pair that has already been bound
to another socket.
EADDRNOTAVAIL
A bind() operation was attempted for an address that
is not configured on this machine.
EINVAL
A sendmsg() operation with a non-NULL msg_accrights
was attempted.
EINVAL
A getsockopt() or setsockopt() operation with an
unknown socket option name was given.
EINVAL
A getsockopt() or setsockopt() operation was attempted
with the IP option field improperly formed; an option
field was shorter than the minimum value or longer
than the option buffer provided.
EISCONN
A connect() operation was attempted on a socket on
which a connect() operation had already been per-
formed, and the socket could not be successfully
disconnected before making the new connection.
EISCONN
A sendto() or sendmsg() operation specifying an
address to which the message should be sent was
attempted on a socket on which a connect() operation
had already been performed.
EMSGSIZE
A send(), sendto(), or sendmsg() operation was
attempted to send a datagram that was too large for an
interface, but was not allowed to be fragmented (such
as broadcasts).
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Protocols ip(7P)
ENETUNREACH
An attempt was made to establish a connection via con-
nect(), or to send a datagram via sendto() or
sendmsg(), where there was no matching entry in the
routing table; or if an ICMP "destination unreachable"
message was received.
ENOTCONN
A send() or write() operation, or a sendto() or
sendmsg() operation not specifying an address to which
the message should be sent, was attempted on a socket
on which a connect() operation had not already been
performed.
ENOBUFS
The system ran out of memory for fragmentation buffers
or other internal data structures.
NOTES
Raw sockets should receive ICMP error packets relating to
the protocol; currently such packets are simply discarded.
Users of higher-level protocols such as TCP and UDP should
be able to see received IP options.
SunOS 5.8 Last change: 23 Feb 2000 6
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