DIVERT(4)                 OpenBSD Programmer's Manual                DIVERT(4)

NAME
     divert - kernel packet diversion mechanism

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>
     #include <netinet/in.h>

     int
     socket(AF_INET, SOCK_RAW, IPPROTO_DIVERT);

     int
     socket(AF_INET6, SOCK_RAW, IPPROTO_DIVERT);

DESCRIPTION
     Divert sockets are part of a mechanism completely integrated with pf(4)
     that queues raw packets from the kernel stack to userspace applications,
     and vice versa.

     A divert socket must be bound to a divert port through bind(2), which on-
     ly the superuser can do.  Divert ports have their own number space, com-
     pletely separated from tcp(4) and udp(4).  When pf(4) processes a packet
     that matches a divert rule (see pf.conf(5) for details) it is immediately
     sent to the divert socket listening on the port specified in the rule.
     pf(4) reassembles TCP streams by default (if IP reassembly is not dis-
     abled) before sending them to the divert sockets.  If there are no divert
     sockets listening, the packets are dropped.

     Packets can be read via read(2), recv(2), or recvfrom(2) from the divert
     socket.  The application that is processing the packets can then reinject
     them into the kernel.  After being reinjected, inbound and outbound pack-
     ets are treated differently.  Inbound packets are added to the relevant
     input queue and a soft interrupt is scheduled to signal that a new packet
     is ready to be processed; outbound ones are processed directly by the
     relevant IP/IPv6 output function.  The packets' checksums are recalculat-
     ed upon reinjection.

     Writing to a divert socket can be achieved using sendto(2) and it will
     skip pf(4) filters to avoid loops.  A diverted packet that is not rein-
     jected into the kernel stack is lost.

     Receive and send divert socket buffer space can be tuned through
     sysctl(8).  netstat(1) shows information relevant to divert sockets.

SEE ALSO
     socket(2), ip(4), pf.conf(5)

HISTORY
     The divert protocol first appeared in OpenBSD 4.7.

OpenBSD 4.7                    December 6, 2009                              1
