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NAME    [Toc]    [Back]

       raw, SOCK_RAW - Linux IPv4 raw sockets

SYNOPSIS    [Toc]    [Back]

       #include <sys/socket.h>
       #include <netinet/in.h>
       raw_socket = socket(PF_INET, SOCK_RAW, int protocol);

DESCRIPTION    [Toc]    [Back]

       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.

       |IP Header fields modified on sending by IP_HDRINCL |
       |IP Checksum	      |Always filled in.	   |
       |Source Address	      |Filled in when zero.	   |
       |Packet Id	      |Filled in when zero.	   |
       |Total Length	      |Always filled in.	   |

       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    [Toc]    [Back]

       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 <netinet/in.h> include file for valid IP

SOCKET OPTIONS    [Toc]    [Back]

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

       ICMP_FILTER    [Toc]    [Back]
	      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    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

	      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    [Toc]    [Back]
	      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    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       This man page was written by Andi Kleen.

SEE ALSO    [Toc]    [Back]

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

       RFC1191 for path MTU discovery.

       RFC791 and the <linux/ip.h> include file for the IP protocol.

Linux Man Page			  1998-10-02				RAW(7)
[ Back ]
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