'\" t
-.\" Don't change the first line, it tells man that we need tbl.
.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
+.\"
+.\" %%%LICENSE_START(VERBATIM_ONE_PARA)
.\" Permission is granted to distribute possibly modified copies
.\" of this page provided the header is included verbatim,
.\" and in case of nontrivial modification author and date
.\" of the modification is added to the header.
-.\" Please send bug reports, corrections and suggestions for improvements to
-.\" <ak@muc.de>
+.\" %%%LICENSE_END
+.\"
.\" $Id: raw.7,v 1.6 1999/06/05 10:32:08 freitag Exp $
-.TH RAW 7 1998-10-02 "Linux Man Page" "Linux Programmer's Manual"
+.\"
+.TH RAW 7 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
-raw, SOCK_RAW \- Linux IPv4 raw sockets
+raw \- Linux IPv4 raw sockets
.SH SYNOPSIS
.B #include <sys/socket.h>
.br
.B #include <netinet/in.h>
.br
-.BI "raw_socket = socket(PF_INET, SOCK_RAW, int " protocol );
-
+.BI "raw_socket = socket(AF_INET, SOCK_RAW, int " protocol );
.SH 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.
-
+A raw socket receives or sends the raw datagram not
+including link level headers.
+.PP
The IPv4 layer generates an IP header when sending a packet unless the
.B 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
-.B CAP_NET_RAW
-capability are allowed to open raw sockets.
-
+For receiving, the IP header is always included in the packet.
+.PP
+In order to create a raw socket, a process must have the
+.B CAP_NET_RAW
+capability in the user namespace that governs its network namespace.
+.PP
All packets or errors matching the
.I protocol
number specified
-for the raw socket are passed to this socket. For a list of the
-allowed protocols see RFC1700 assigned numbers and
+for the raw socket are passed to this socket.
+For a list of the allowed protocols,
+see the IANA list of assigned protocol numbers at
+.UR http://www.iana.org/assignments/protocol\-numbers/
+.UE
+and
.BR getprotobyname (3).
-
+.PP
A protocol of
.B IPPROTO_RAW
implies enabled
-.B IP_HDRINCL
-and is able to send any IP protocol that is specified in the passed header.
+.B IP_HDRINCL
+and is able to send any IP protocol that is specified in the passed
+header.
Receiving of all IP protocols via
.B IPPROTO_RAW
is not possible using raw sockets.
-
+.RS
.TS
tab(:) allbox;
c s
l l.
-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.
+IP Header fields modified on sending by \fBIP_HDRINCL\fP
+IP Checksum:Always filled in
+Source Address:Filled in when zero
+Packet ID:Filled in when zero
+Total Length:Always filled in
.TE
+.RE
.PP
-
-If
+.PP
+If
.B 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
+is specified and the IP header has a nonzero destination address, then
+the destination address of the socket is used to route the packet.
+When
.B MSG_DONTROUTE
-is specified the destination address should refer to a local interface,
-otherwise a routing table lookup is done anyways but gatewayed routes
+is specified, the destination address should refer to a local interface,
+otherwise a routing table lookup is done anyway but gatewayed routes
are ignored.
-
+.PP
If
.B IP_HDRINCL
-isn't set then IP header options can be set on raw sockets with
+isn't set, then IP header options can be set on raw sockets with
.BR setsockopt (2);
see
-.BR ip (7)
+.BR 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
+.PP
+Starting with Linux 2.2, all IP header fields and options can be set using
+IP socket options.
+This means raw sockets are usually needed only for new
protocols or protocols with no user interface (like ICMP).
-
+.PP
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).
-
-.SH "ADDRESS FORMAT"
-
-Raw sockets use the standard
-.B sockaddr_in
-address structure defined in
+(e.g., kernel protocol modules).
+.SS Address format
+For sending and receiving datagrams
+.RB ( sendto (2),
+.BR recvfrom (2),
+and similar),
+raw sockets use the standard
+.I sockaddr_in
+address structure defined in
.BR ip (7).
-The
-The
-.B 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
-.B sin_port
-is set to the protocol of the packet.
-See the
-.B <netinet/in.h>
-include file for valid IP protocols.
-
-.SH "SOCKET OPTIONS"
+The
+.I sin_port
+field could be used to specify the IP protocol number,
+but it is ignored for sending in Linux 2.2 and later, and should be always
+set to 0 (see BUGS).
+For incoming packets,
+.I sin_port
+.\" commit f59fc7f30b710d45aadf715460b3e60dbe9d3418
+is set to zero.
+.SS Socket options
Raw socket options can be set with
.BR setsockopt (2)
and read with
.BR getsockopt (2)
-by passing the
-.I SOL_RAW
-family flag.
-
+by passing the
+.B IPPROTO_RAW
+.\" Or SOL_RAW on Linux
+family flag.
.TP
.B ICMP_FILTER
-Enable a special filter for raw sockets bound to the
-.B 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.
-
+Enable a special filter for raw sockets bound to the
+.B 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.
.PP
-In addition all
+In addition, all
.BR ip (7)
-.B SOL_IP
+.B IPPROTO_IP
socket options valid for datagram sockets are supported.
-
+.SS Error handling
+Errors originating from the network are passed to the user only when the
+socket is connected or the
+.B IP_RECVERR
+flag is enabled.
+For connected sockets, only
+.B EMSGSIZE
+and
+.B EPROTO
+are passed for compatibility.
+With
+.BR IP_RECVERR ,
+all network errors are saved in the error queue.
+.SH ERRORS
+.TP
+.B EACCES
+User tried to send to a broadcast address without having the
+broadcast flag set on the socket.
+.TP
+.B EFAULT
+An invalid memory address was supplied.
+.TP
+.B EINVAL
+Invalid argument.
+.TP
+.B EMSGSIZE
+Packet too big.
+Either Path MTU Discovery is enabled (the
+.B IP_MTU_DISCOVER
+socket flag) or the packet size exceeds the maximum allowed IPv4
+packet size of 64\ kB.
+.TP
+.B EOPNOTSUPP
+Invalid flag has been passed to a socket call (like
+.BR MSG_OOB ).
+.TP
+.B EPERM
+The user doesn't have permission to open raw sockets.
+Only processes with an effective user ID of 0 or the
+.B CAP_NET_RAW
+attribute may do that.
+.TP
+.B EPROTO
+An ICMP error has arrived reporting a parameter problem.
+.SH VERSIONS
+.B IP_RECVERR
+and
+.B ICMP_FILTER
+are new in Linux 2.2.
+They are Linux extensions and should not be used in portable programs.
+.PP
+Linux 2.0 enabled some bug-to-bug compatibility with BSD in the
+raw socket code when the
+.B SO_BSDCOMPAT
+socket option was set; since Linux 2.2,
+this option no longer has that effect.
.SH 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
-.B IP_MTU_DISCOVER
-section of
-.BR ip (7).
-
-A raw socket can be bound to a specific local address using the
+By default, raw sockets do path MTU (Maximum Transmission Unit) discovery.
+This means the kernel
+will keep track of the MTU to a specific target IP address and return
+.B EMSGSIZE
+when a raw packet write exceeds it.
+When this happens, the application should decrease the packet size.
+Path MTU discovery can be also turned off using the
+.B IP_MTU_DISCOVER
+socket option or the
+.I /proc/sys/net/ipv4/ip_no_pmtu_disc
+file, see
+.BR ip (7)
+for details.
+When turned off, raw sockets will fragment outgoing packets
+that exceed the interface MTU.
+However, disabling it is not recommended
+for performance and reliability reasons.
+.PP
+A raw socket can be bound to a specific local address using the
.BR 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
-.B SO_BINDTODEVICE;
-see
+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
+.BR SO_BINDTODEVICE ;
+see
.BR socket (7).
-
+.PP
An
.B IPPROTO_RAW
socket is send only.
-If you really want to receive all IP packets use a
+If you really want to receive all IP packets, use a
.BR packet (7)
socket with the
.B 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
+protocol.
+Note that packet sockets don't reassemble IP fragments,
+unlike raw sockets.
+.PP
+If you want to receive all ICMP packets for a datagram socket,
+it is often better to use
.B IP_RECVERR
on that particular socket; see
.BR ip (7).
-
+.PP
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
+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
+.PP
+Linux never changes headers passed from the user (except for filling
+in some zeroed fields as described for
.BR 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
-.B sin_port;
-this ability was lost in Linux 2.2. Work around is to use
-.B IP_HDRINCL.
-
-.SH "ERROR HANDLING"
-Errors originating from the network are only passed to the user when the
-socket is connected or the
-.B IP_RECVERR
-flag is enabled. For connected sockets only
-.B EMSGSIZE
-and
-.B EPROTO
-are passed for compatibility. With
-.B IP_RECVERR
-all network errors are saved in the error queue.
-.SH ERRORS
-.TP
-.B EMSGSIZE
-Packet too big. Either Path MTU Discovery is enabled (the
-.B IP_MTU_DISCOVER
-socket flag) or the packet size exceeds the maximum allowed IPv4 packet size
-of 64KB.
-.TP
-.B EACCES
-User tried to send to a broadcast address without having the broadcast flag
-set on the socket.
-.TP
-.B EPROTO
-An ICMP error has arrived reporting a parameter problem.
-.TP
-.B EFAULT
-An invalid memory address was supplied.
-.TP
-.B EOPNOTSUPP
-Invalid flag has been passed to a socket call (like
-.BR MSG_OOB ).
-.TP
-.B EINVAL
-Invalid argument.
-.TP
-.B EPERM
-The user doesn't have permission to open raw sockets. Only processes
-with a effective user id of 0 or the
-.B CAP_NET_RAW
-attribute may do that.
-
-.SH VERSIONS
-.B IP_RECVERR
-and
-.B 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.
-
+.PP
+Raw sockets are generally rather unportable and should be avoided in
+programs intended to be portable.
+.PP
+Sending on raw sockets should take the IP protocol from
+.IR sin_port ;
+this ability was lost in Linux 2.2.
+The workaround is to use
+.BR IP_HDRINCL .
.SH BUGS
Transparent proxy extensions are not described.
-
-When the
+.PP
+When the
.B 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.
-
+option is set, datagrams will not be fragmented and are limited to
+the interface MTU.
+.PP
Setting the IP protocol for sending in
-.B sin_port
-got lost in Linux 2.2. The protocol that socket was bound to or that
-was specified in the initial
+.I sin_port
+got lost in Linux 2.2.
+The protocol that the socket was bound to or that
+was specified in the initial
.BR socket (2)
call is always used.
-
-.SH AUTHORS
-This man page was written by Andi Kleen.
-
-.SH "SEE ALSO"
+.\" .SH AUTHORS
+.\" This man page was written by Andi Kleen.
+.SH SEE ALSO
.BR recvmsg (2),
.BR sendmsg (2),
.BR capabilities (7),
.BR ip (7),
.BR socket (7)
-
-.B RFC1191
+.PP
+.B RFC\ 1191
for path MTU discovery.
-
-.B RFC791
+.B RFC\ 791
and the
-.B <linux/ip.h>
-include file for the IP protocol.
+.I <linux/ip.h>
+header file for the IP protocol.
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