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RAW
!!!RAW
NAME
SYNOPSIS
DESCRIPTION
ADDRESS FORMAT
SOCKET OPTIONS
NOTES
ERROR HANDLING
ERRORS
VERSIONS
BUGS
AUTHORS
SEE ALSO
----
!!NAME


raw, SOCK_RAW - Linux IPv4 raw sockets
!!SYNOPSIS


__#include __
#include __
raw_socket = socket(PF_INET, SOCK_RAW, int__
''protocol''__);__
!!DESCRIPTION


Raw sockets allow new IPv4 protocols to be implemented in
user space. A raw socket receives or sends the raw datagram
not including link level headers.


The IPv4 layer generates an IP header when sending a packet
unless the __IP_HDRINCL__ socket option is enabled on the
socket. When it is enabled, the packet must contain an IP
header. For receiving the IP header is always included in
the packet.


Only processes with an effective user id of 0 or the
__CAP_NET_RAW__ capability are allowed to open raw
sockets.


All packets or errors matching the ''protocol'' number
specified for the raw socket are passed to this socket. For
a list of the allowed protocols see RFC1700 assigned numbers
and getprotobyname(3).


A protocol of __IPPROTO_RAW__ implies enabled
__IP_HDRINCL__ and receives all IP protocols. Sending is
not allowed.


If __IP_HDRINCL__ is specified and the IP header has a non-zero destination address then the destination address of the socket is used to route the packet. When __MSG_DONTROUTE__ is specified the destination address should refer to a local interface, otherwise a routing table lookup is done anyways but gatewayed routes are ignored.


If __IP_HDRINCL__ isn't set then IP header options can be
set on raw sockets with setsockopt(2); see
ip(7) for more information.


In Linux 2.2 all IP header fields and options can be set
using IP socket options. This means raw sockets are usually
only needed for new protocols or protocols with no user
interface (like ICMP).


When a packet is received, it is passed to any raw sockets
which have been bound to its protocol before it is passed to
other protocol handlers (e.g. kernel protocol
modules).
!!ADDRESS FORMAT


Raw sockets use the standard __sockaddr_in__ address
structure defined in ip(7). The The __sin_port__
field could be used to specify the IP protocol number, but
it is ignored for sending in Linux 2.2 and should be always
set to 0 (see BUGS) For incoming packets __sin_port__ is
set to the protocol of the packet. See the
____ include file for valid IP
protocols.
!!SOCKET OPTIONS


Raw socket options can be set with setsockopt(2) and
read with getsockopt(2) by passing the ''SOL_RAW''
family flag.


__ICMP_FILTER__


Enable a special filter for raw sockets bound to the
__IPPROTO_ICMP__ protocol. The value has a bit set for
each ICMP message type which should be filtered out. The
default is to filter no ICMP messages.


In addition all ip(7) __SOL_IP__ socket options
valid for datagram sockets are supported.
!!NOTES


Raw sockets fragment a packet when its total length exceeds
the interface MTU (but see BUGS). A more network friendly
and faster alternative is to implement path MTU discovery as
described in the __IP_PMTU_DISCOVER__ section of
ip(7).


A raw socket can be bound to a specific local address using
the bind(2) call. If it isn't bound all packets with
the specified IP protocol are received. In addition a RAW
socket can be bound to a specific network device using
__SO_BINDTODEVICE;__ see socket(7).


An __IPPROTO_RAW__ socket is send only. If you really
want to receive all IP packets use a packet(7) socket
with the __ETH_P_IP__ protocol. Note that packet sockets
don't reassemble IP fragments, unlike raw
sockets.


If you want to receive all ICMP packets for a datagram
socket it is often better to use __IP_RECVERR__ on that
particular socket; see ip(7).


Raw sockets may tap all IP protocols in Linux, even
protocols like ICMP or TCP which have a protocol module in
the kernel. In this case the packets are passed to both the
kernel module and the raw socket(s). This should not be
relied upon in portable programs, many other BSD socket
implementation have limitations here.


Linux never changes headers passed from the user (except for
filling in some zeroed fields as described for
__IP_HDRINCL__). This differs from many other
implementations of raw sockets.


RAW sockets are generally rather unportable and should be
avoided in programs intended to be portable.


Sending on raw sockets should take the IP protocol from
__sin_port;__ this ability was lost in Linux 2.2. Work
around is to use __IP_HDRINCL.__
!!ERROR HANDLING


Errors originating from the network are only passed to the
user when the socket is connected or the __IP_RECVERR__
flag is enabled. For connected sockets only __EMSGSIZE__
and __EPROTO__ are passed for compatibility. With
__IP_RECVERR__ all network errors are saved in the error
queue.
!!ERRORS


__EMSGSIZE__


Packet too big. Either Path MTU Discovery is enabled (the
__IP_PMTU_DISCOVER__ socket flag) or the packet size
exceeds the maximum allowed IPv4 packet size of
64KB.


__EACCES__


User tried to send to a broadcast address without having the
broadcast flag set on the socket.


__EPROTO__


An ICMP error has arrived reporting a parameter
problem.


__EFAULT__


An invalid memory address was supplied.


__EOPNOTSUPP__


Invalid flag has been passed to a socket call (like
__MSG_OOB__).


__EINVAL__


Invalid argument.


__EPERM__


The user doesn't have permission to open raw sockets. Only
processes with a effective user id of 0 or the
__CAP_NET_RAW__ attribute may do that.
!!VERSIONS


__IP_RECVERR__ and __ICMP_FILTER__ are new in Linux
2.2. They are Linux extensions and should not be used in
portable programs.


Linux 2.0 enabled some bug-to-bug compatibility with BSD in
the raw socket code when the SO_BSDCOMPAT flag was set -
that has been removed in 2.2.
!!BUGS


Transparent proxy extensions are not described.


When the __IP_HDRINCL__ option is set datagrams will not
be fragmented and are limited to the interface MTU. This is
a limitation in Linux 2.2.


Setting the IP protocol for sending in __sin_port__ got
lost in Linux 2.2. The protocol that socket was bound to or
that was specified in the initial socket(2) call is
always used.
!!AUTHORS


This man page was written by Andi Kleen.
!!SEE ALSO


ip(7), socket(7), recvmsg(2),
sendmsg(2)


__RFC1191__ for path MTU discovery.


__RFC791__ and the ____ include file
for the IP protocol.
----
5 pages link to raw(7):
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Last edited on Tuesday, June 4, 2002 12:30:59 am by "perry"
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