236 lines
7.3 KiB
Groff
236 lines
7.3 KiB
Groff
.\" Copyright (c) 2010 Maxim Ignatenko <gelraen.ua@gmail.com>
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.\" Copyright (c) 2010 Vadim Goncharov <vadimnuclight@tpu.ru>
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, 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 March 5, 2012
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.Dt NG_PATCH 4
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.Os
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.Sh NAME
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.Nm ng_patch
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.Nd "trivial mbuf data modifying netgraph node type"
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.Sh SYNOPSIS
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.In netgraph/ng_patch.h
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.Sh DESCRIPTION
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The
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.Nm patch
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node performs data modification of packets passing through it.
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Modifications are restricted to a subset of C language operations
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on unsigned integers of 8, 16, 32 or 64 bit size.
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These are: set to new value (=), addition (+=), subtraction (-=),
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multiplication (*=), division (/=), negation (= -),
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bitwise AND (&=), bitwise OR (|=), bitwise eXclusive OR (^=),
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shift left (<<=), shift right (>>=).
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A negation operation is the one exception: integer is treated as signed
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and second operand (the
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.Va value )
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is not used.
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There may be several modification operations, they are all applied
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to a packet sequentially in order they were specified by user.
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Data payload of packet is viewed as array of bytes, with zero offset
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corresponding to the very first byte of packet headers, and
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.Va length
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bytes beginning from
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.Va offset
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are taken as a single integer in network byte order.
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.Sh HOOKS
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This node type has two hooks:
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.Bl -tag -width ".Va out"
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.It Va in
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Packets received on this hook are modified according to rules specified
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in config and then forwarded to
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.Ar out
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hook, if it exists and connected.
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Otherwise they are reflected back to the
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.Ar in
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hook.
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.It Va out
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Packets received on this hook are forwarded to
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.Ar in
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hook without any changes.
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.El
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.Sh CONTROL MESSAGES
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This node type supports the generic control messages, plus the following:
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.Bl -tag -width foo
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.It Dv NGM_PATCH_SETCONFIG Pq Ic setconfig
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This command sets the sequence of modify operations
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that will be applied to incoming data on a hook.
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The following
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.Vt "struct ng_patch_config"
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must be supplied as an argument:
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.Bd -literal -offset 4n
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struct ng_patch_op {
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uint64_t value;
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uint32_t offset;
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uint16_t length; /* 1,2,4 or 8 bytes */
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uint16_t mode;
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};
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/* Patching modes */
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#define NG_PATCH_MODE_SET 1
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#define NG_PATCH_MODE_ADD 2
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#define NG_PATCH_MODE_SUB 3
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#define NG_PATCH_MODE_MUL 4
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#define NG_PATCH_MODE_DIV 5
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#define NG_PATCH_MODE_NEG 6
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#define NG_PATCH_MODE_AND 7
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#define NG_PATCH_MODE_OR 8
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#define NG_PATCH_MODE_XOR 9
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#define NG_PATCH_MODE_SHL 10
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#define NG_PATCH_MODE_SHR 11
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struct ng_patch_config {
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uint32_t count;
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uint32_t csum_flags;
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struct ng_patch_op ops[];
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};
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.Ed
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.Pp
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The
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.Va csum_flags
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can be set to any combination of CSUM_IP, CSUM_TCP, CSUM_SCTP and CSUM_UDP
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(other values are ignored) for instructing the IP stack to recalculate the
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corresponding checksum before transmitting packet on output interface.
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The
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.Nm
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node does not do any checksum correction by itself.
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.It Dv NGM_PATCH_GETCONFIG Pq Ic getconfig
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This control message obtains current set of modify operations,
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returned as
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.Vt "struct ng_patch_config" .
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.It Dv NGM_PATCH_GET_STATS Pq Ic getstats
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Returns node statistics as a
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.Vt "struct ng_patch_stats" .
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.It Dv NGM_PATCH_CLR_STATS Pq Ic clrstats
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Clear node statistics.
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.It Dv NGM_PATCH_GETCLR_STATS Pq Ic getclrstats
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This command is identical to
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.Dv NGM_PATCH_GET_STATS ,
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except that the statistics are also atomically cleared.
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.El
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.Sh SHUTDOWN
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This node shuts down upon receipt of a
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.Dv NGM_SHUTDOWN
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control message, or when all hooks have been disconnected.
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.Sh EXAMPLES
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The
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.Nm
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node allows to modify TTL and TOS/DSCP fields in IP packets.
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Suppose you have two adjacent simplex links to remote network
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(e.g.\& satellite), so that the packets expiring in between
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will generate unwanted ICMP-replies which have to go forth, not back.
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Thus you need to raise TTL of every packet entering link by 2
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to ensure the TTL will not reach zero there.
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So you setup
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.Xr ipfw 8
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rule with
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.Cm netgraph
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action to inject packets going to other end of simplex link by the
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following
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.Xr ngctl 8
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script:
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.Bd -literal -offset 4n
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/usr/sbin/ngctl -f- <<-SEQ
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mkpeer ipfw: patch 200 in
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name ipfw:200 ttl_add
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msg ttl_add: setconfig { count=1 csum_flags=1 ops=[ \e
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{ mode=2 value=3 length=1 offset=8 } ] }
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SEQ
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/sbin/ipfw add 150 netgraph 200 ip from any to simplex.remote.net
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.Ed
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.Pp
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Here
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.Dq Li ttl_add
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node of type
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.Nm
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configured to add (mode
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.Dv NG_PATCH_MODE_ADD )
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a
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.Va value
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of 3 to a one-byte TTL field, which is 9th byte of IP packet header.
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.Pp
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Another example would be two consecutive modifications of packet TOS
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field: say, you need to clear the
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.Dv IPTOS_THROUGHPUT
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bit and set the
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.Dv IPTOS_MINCOST
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bit.
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So you do:
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.Bd -literal -offset 4n
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/usr/sbin/ngctl -f- <<-SEQ
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mkpeer ipfw: patch 300 in
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name ipfw:300 tos_chg
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msg tos_chg: setconfig { count=2 csum_flags=1 ops=[ \e
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{ mode=7 value=0xf7 length=1 offset=1 } \e
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{ mode=8 value=0x02 length=1 offset=1 } ] }
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SEQ
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/sbin/ipfw add 160 netgraph 300 ip from any to any not dst-port 80
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.Ed
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.Pp
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This first does
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.Dv NG_PATCH_MODE_AND
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clearing the fourth bit and then
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.Dv NG_PATCH_MODE_OR
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setting the third bit.
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.Pp
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In both examples the
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.Va csum_flags
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field indicates that IP checksum (but not TCP or UDP checksum) should be
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recalculated before transmit.
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.Pp
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Note: one should ensure that packets are returned to ipfw after processing
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inside
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.Xr netgraph 4 ,
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by setting appropriate
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.Xr sysctl 8
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variable:
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.Bd -literal -offset 4n
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sysctl net.inet.ip.fw.one_pass=0
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.Ed
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.Sh SEE ALSO
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.Xr netgraph 4 ,
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.Xr ng_ipfw 4 ,
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.Xr ngctl 8
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.Sh HISTORY
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The
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.Nm
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node type was implemented in
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.Fx 8.1 .
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.Sh AUTHORS
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.An "Maxim Ignatenko" Aq gelraen.ua@gmail.com .
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This manual page was written by
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.An "Vadim Goncharov" Aq vadimnuclight@tpu.ru .
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.Sh BUGS
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Node blindly tries to apply every patching operation to each packet
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(except those which offset if greater than length of the packet),
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so be sure that you supply only the right packets to it (e.g. changing
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bytes in the ARP packets meant to be in IP header could corrupt
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them and make your machine unreachable from the network).
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.Pp
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.Em !!! WARNING !!!
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.Pp
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Output path of the IP stack assumes correct fields and lengths in the
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packets - changing them by mistake to incorrect values can cause
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unpredictable results including kernel panics.
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