c21fd23260
compile option. All FreeBSD packet filters now use the PFIL_HOOKS API and thus it becomes a standard part of the network stack. If no hooks are connected the entire packet filter hooks section and related activities are jumped over. This removes any performance impact if no hooks are active. Both OpenBSD and DragonFlyBSD have integrated PFIL_HOOKS permanently as well.
211 lines
5.9 KiB
Groff
211 lines
5.9 KiB
Groff
.\" $NetBSD: pfil.9,v 1.22 2003/07/01 13:04:06 wiz Exp $
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.\"
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.\" Copyright (c) 1996 Matthew R. Green
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd September 8, 2003
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.Dt PFIL 9
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.Os
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.Sh NAME
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.Nm pfil ,
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.Nm pfil_head_register ,
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.Nm pfil_head_unregister ,
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.Nm pfil_head_get ,
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.Nm pfil_hook_get ,
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.Nm pfil_add_hook ,
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.Nm pfil_remove_hook ,
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.Nm pfil_run_hooks
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.Nd packet filter interface
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/mbuf.h
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.In net/if.h
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.In net/pfil.h
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.Ft int
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.Fn pfil_head_register "struct pfil_head *head"
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.Ft int
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.Fn pfil_head_unregister "struct pfil_head *head"
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.Ft "struct pfil_head *"
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.Fn pfil_head_get "int af" "u_long dlt"
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.Ft "struct packet_filter_hook *"
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.Fn pfil_hook_get "int dir" "struct pfil_head *head"
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.Ft void
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.Fn pfil_add_hook "int (*func)()" "void *arg" "int flags" "struct pfil_head *"
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.Ft void
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.Fn pfil_remove_hook "int (*func)()" "void *arg" "int flags" "struct pfil_head *"
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.Ft int
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.Fn (*func) "void *arg" "struct mbuf **mp" "struct ifnet *" "int dir"
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.Ft int
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.Fn pfil_run_hooks "struct pfil_head *head" "struct mbuf **mp" "struct ifnet *" "int dir"
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.Sh DESCRIPTION
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The
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.Nm
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framework allows for a specified function to be invoked for every
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incoming or outgoing packet for a particular network I/O stream.
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These hooks may be used to implement a firewall or perform packet
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transformations.
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.Pp
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Packet filtering points are registered with
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.Fn pfil_head_register .
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Filtering points are identified by a key
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.Pq Vt "void *"
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and a data link type
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.Pq Vt int
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in the
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.Vt pfil_head
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structure.
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Packet filters use the key and data link type to look up the filtering
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point with which they register themselves.
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The key is unique to the filtering point.
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The data link type is a
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.Xr bpf 4
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DLT constant indicating what kind of header is present on the packet
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at the filtering point.
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Filtering points may be unregistered with the
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.Fn pfil_head_unregister
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function.
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.Pp
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Packet filters register/unregister themselves with a filtering point
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with the
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.Fn pfil_add_hook
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and
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.Fn pfil_remove_hook
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functions, respectively.
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The head is looked up using the
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.Fn pfil_head_get
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function, which takes the key and data link type that the packet filter
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expects.
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Filters may provide an argument to be passed to the filter when
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invoked on a packet.
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.Pp
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When a filter is invoked, the packet appears just as if it
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.Dq came off the wire .
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That is, all protocol fields are in network byte order.
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The filter is called with its specified argument, the pointer to the
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pointer to the
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.Vt mbuf
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containing the packet, the pointer to the network
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interface that the packet is traversing, and the direction
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.Dv ( PFIL_IN
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or
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.Dv PFIL_OUT )
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that the packet is traveling.
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The filter may change which mbuf the
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.Vt "mbuf\ **"
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argument references.
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The filter returns an error (errno) if the packet processing is to stop, or 0
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if the processing is to continue.
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If the packet processing is to stop, it is the responsibility of the
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filter to free the packet.
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.Sh RETURN VALUES
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If successful,
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.Fn pfil_head_get
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returns the
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.Vt pfil_head
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structure for the given key/dlt.
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The
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.Fn pfil_add_hook
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and
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.Fn pfil_remove_hook
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functions
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return 0 if successful.
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If called with flag
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.Dv PFIL_WAITOK ,
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.Fn pfil_remove_hook
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is expected to always succeed.
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.Pp
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The
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.Fn pfil_head_unregister
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function
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might sleep!
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.Sh HISTORY
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The
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.Nm
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interface first appeared in
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.Nx 1.3 .
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The
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.Nm
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input and output lists were originally implemented as
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.In sys/queue.h
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.Dv LIST
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structures;
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however this was changed in
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.Nx 1.4
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to
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.Dv TAILQ
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structures.
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This change was to allow the input and output filters to be processed in
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reverse order, to allow the same path to be taken, in or out of the kernel.
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.Pp
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The
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.Nm
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interface was changed in 1.4T to accept a 3rd parameter to both
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.Fn pfil_add_hook
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and
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.Fn pfil_remove_hook ,
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introducing the capability of per-protocol filtering.
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This was done primarily in order to support filtering of IPv6.
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.Pp
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In 1.5K, the
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.Nm
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framework was changed to work with an arbitrary number of filtering points,
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as well as be less IP-centric.
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.Pp
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Fine-grained locking was added in
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.Fx 5.2 .
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.Sh BUGS
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The
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.Fn pfil_hook_get
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function
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is only safe for internal use.
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.Pp
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.Fx
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implements only hooks for
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.Dv AF_INET
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and
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.Dv AF_INET6 .
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Packets diverted through these hooks have data in
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host byte order contrary to the above statements.
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.Pp
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The
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.Xr bridge 4
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diverts inbound
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.Dv AF_INET
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traffic, but contrary to the above
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statements, the data is provided in host byte order.
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.Pp
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When a
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.Vt pfil_head
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is being modified, no traffic is diverted
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(to avoid deadlock).
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This means that unwanted traffic may flow for a short period
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of time.
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.Sh SEE ALSO
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.Xr bpf 4 ,
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.Xr bridge 4
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