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RAW(7)				    Linux Programmer's Manual				   RAW(7)

       raw, SOCK_RAW - Linux IPv4 raw sockets

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

       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 get-

       A  protocol  of IPPROTO_RAW implies enabled IP_HDRINCL and is able to send any IP protocol
       that is specified in the passed header.	Receiving of all IP protocols via IPPROTO_RAW  is
       not possible using raw sockets.

       |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 spec-
       ified 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  setsock-
       opt(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).

       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 protocols.

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

	      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.

       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  sock-

       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.

       Errors  originating  from  the network are only passed to the user when the socket is con-
       nected 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

	      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.

	      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  effec-
	      tive user id of 0 or the CAP_NET_RAW attribute may do that.

       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.

       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.

       This man page was written by Andi Kleen.

       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)
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