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+.\" Copyright (c) 1983, 1986, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"	This product includes software developed by the University of
+.\"	California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"	@(#)b.t	8.1 (Berkeley) 6/8/93
+.\"
+.nr H2 1
+.\".ds RH "Raw sockets
+.br
+.ne 2i
+.NH
+\s+2Raw sockets\s0
+.PP
+A raw socket is an object which allows users direct access
+to a lower-level protocol.  Raw sockets are intended for knowledgeable
+processes which wish to take advantage of some protocol
+feature not directly accessible through the normal interface, or 
+for the development of new protocols built atop existing lower level
+protocols.  For example, a new version of TCP might be developed at the
+user level by utilizing a raw IP socket for delivery of packets.
+The raw IP socket interface attempts to provide an identical interface
+to the one a protocol would have if it were resident in the kernel.
+.PP
+The raw socket support is built around a generic raw socket interface,
+(possibly) augmented by protocol-specific processing routines.
+This section will describe the core of the raw socket interface.
+.NH 2
+Control blocks
+.PP
+Every raw socket has a protocol control block of the following form:
+.DS
+.ta \w'struct  'u +\w'caddr_t  'u +\w'sockproto rcb_proto;    'u 
+struct rawcb {
+	struct	rawcb *rcb_next;	/* doubly linked list */
+	struct	rawcb *rcb_prev;
+	struct	socket *rcb_socket;	/* back pointer to socket */
+	struct	sockaddr rcb_faddr;	/* destination address */
+	struct	sockaddr rcb_laddr;	/* socket's address */
+	struct	sockproto rcb_proto;	/* protocol family, protocol */
+	caddr_t	rcb_pcb;		/* protocol specific stuff */
+	struct	mbuf *rcb_options;	/* protocol specific options */
+	struct	route rcb_route;	/* routing information */
+	short	rcb_flags;
+};
+.DE
+All the control blocks are kept on a doubly linked list for
+performing lookups during packet dispatch.  Associations may
+be recorded in the control block and used by the output routine
+in preparing packets for transmission.
+The \fIrcb_proto\fP structure contains the protocol family and protocol
+number with which the raw socket is associated.
+The protocol, family and addresses are
+used to filter packets on input; this will be described in more
+detail shortly.  If any protocol-specific information is required,
+it may be attached to the control block using the \fIrcb_pcb\fP
+field.
+Protocol-specific options for transmission in outgoing packets
+may be stored in \fIrcb_options\fP.
+.PP
+A raw socket interface is datagram oriented.  That is, each send
+or receive on the socket requires a destination address.  This
+address may be supplied by the user or stored in the control block
+and automatically installed in the outgoing packet by the output
+routine.  Since it is not possible to determine whether an address
+is present or not in the control block, two flags, RAW_LADDR and
+RAW_FADDR, indicate if a local and foreign address are present.
+Routing is expected to be performed by the underlying protocol
+if necessary.
+.NH 2
+Input processing
+.PP
+Input packets are ``assigned'' to raw sockets based on a simple
+pattern matching scheme.  Each network interface or protocol
+gives unassigned packets
+to the raw input routine with the call:
+.DS
+raw_input(m, proto, src, dst)
+struct mbuf *m; struct sockproto *proto, struct sockaddr *src, *dst;
+.DE
+The data packet then has a generic header prepended to it of the
+form
+.DS
+._f
+struct raw_header {
+	struct	sockproto raw_proto;
+	struct	sockaddr raw_dst;
+	struct	sockaddr raw_src;
+};
+.DE
+and it is placed in a packet queue for the ``raw input protocol'' module.
+Packets taken from this queue are copied into any raw sockets that
+match the header according to the following rules,
+.IP 1)
+The protocol family of the socket and header agree.
+.IP 2)
+If the protocol number in the socket is non-zero, then it agrees
+with that found in the packet header.
+.IP 3)
+If a local address is defined for the socket, the address format
+of the local address is the same as the destination address's and
+the two addresses agree bit for bit.
+.IP 4)
+The rules of 3) are applied to the socket's foreign address and the packet's
+source address.
+.LP
+A basic assumption is that addresses present in the
+control block and packet header (as constructed by the network
+interface and any raw input protocol module) are in a canonical
+form which may be ``block compared''.
+.NH 2
+Output processing
+.PP
+On output the raw \fIpr_usrreq\fP routine 
+passes the packet and a pointer to the raw control block to the
+raw protocol output routine for any processing required before
+it is delivered to the appropriate network interface.  The
+output routine is normally the only code required to implement
+a raw socket interface.