DIVERT(4) OpenBSD Programmer's Manual DIVERT(4)NAMEdivert - 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
only the superuser can do. Divert ports have their own number space,
completely 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 disabled) 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
packets 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
recalculated 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
reinjected 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 ALSOsocket(2), ip(4), pf.conf(5)HISTORY
The divert protocol first appeared in OpenBSD 4.7.
OpenBSD 4.9 December 6, 2009 OpenBSD 4.9
