236 lines
7.1 KiB
Groff
236 lines
7.1 KiB
Groff
.\" Copyright (c) 1996-1999 Whistle Communications, Inc.
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.\" All rights reserved.
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.\"
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.\" Subject to the following obligations and disclaimer of warranty, use and
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.\" redistribution of this software, in source or object code forms, with or
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.\" without modifications are expressly permitted by Whistle Communications;
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.\" provided, however, that:
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.\" 1. Any and all reproductions of the source or object code must include the
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.\" copyright notice above and the following disclaimer of warranties; and
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.\" 2. No rights are granted, in any manner or form, to use Whistle
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.\" Communications, Inc. trademarks, including the mark "WHISTLE
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.\" COMMUNICATIONS" on advertising, endorsements, or otherwise except as
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.\" such appears in the above copyright notice or in the software.
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.\"
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.\" THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
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.\" TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO
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.\" REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,
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.\" INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
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.\" WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY
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.\" REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS
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.\" SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.
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.\" IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES
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.\" RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING
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.\" WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
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.\" PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR
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.\" SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY
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.\" OF SUCH DAMAGE.
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.\"
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.\" Author: Archie Cobbs <archie@FreeBSD.org>
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.\"
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.\" $FreeBSD$
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.\" $Whistle: ng_vjc.8,v 1.4 1999/01/25 23:46:28 archie Exp $
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.\"
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.Dd January 19, 1999
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.Dt NG_VJC 4
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.Os
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.Sh NAME
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.Nm ng_vjc
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.Nd Van Jacobson compression netgraph node type
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.Sh SYNOPSIS
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.In net/slcompress.h
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.In netgraph/ng_vjc.h
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.Sh DESCRIPTION
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The
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.Nm vjc
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node type performs Van Jacobson compression, which is used
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over PPP, SLIP, and other point-to-point IP connections to
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compress TCP packet headers.
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The
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.Dv ip
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hook represents the uncompressed side of the node, while the
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.Dv vjcomp ,
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.Dv vjuncomp ,
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and
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.Dv vjip
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hooks represent the compressed side of the node.
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Packets received on the
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.Dv ip
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will be compressed or passed through as appropriate.
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Packets received on the other three hooks will be uncompressed as appropriate.
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This node also supports
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.Dq always pass through
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mode in either direction.
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.Pp
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Van Jacobson compression only applies to TCP packets.
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Only
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.Dq normal
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(i.e., common case) TCP packets are actually compressed.
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These are output on the
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.Dv vjcomp
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hook.
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Other TCP packets are run through the state machine but not
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compressed; these appear on the
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.Dv vjuncomp
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hook.
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Other non-TCP IP packets are forwarded unchanged to
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.Dv vjip .
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.Pp
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When connecting to a
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.Xr ng_ppp 4
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node, the
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.Dv ip ,
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.Dv vjuncomp ,
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.Dv vjcomp ,
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and
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.Dv vjip
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hooks should be connected to the
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.Xr ng_ppp 4
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node's
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.Dv vjc_ip ,
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.Dv vjc_vjcomp ,
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.Dv vjc_vjuncomp ,
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and
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.Dv vjc_ip
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hooks, respectively.
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.Sh HOOKS
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This node type supports the following hooks:
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.Pp
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.Bl -tag -width foobarbazi
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.It Dv ip
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Upstream (uncompressed) IP packets.
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.It Dv vjcomp
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Downstream compressed TCP packets.
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.It Dv vjuncomp
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Downstream uncompressed TCP packets.
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.It Dv vjip
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Downstream uncompressed IP packets.
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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_VJC_SET_CONFIG
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This command resets the compression state and configures it according
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to the supplied
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.Dv "struct ngm_vjc_config"
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argument.
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This structure contains the following fields:
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.Bd -literal -offset 4n
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struct ngm_vjc_config {
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u_char enableComp; /* Enable compression */
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u_char enableDecomp; /* Enable decompression */
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u_char maxChannel; /* Number of outgoing channels - 1 */
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u_char compressCID; /* OK to compress outgoing CID's */
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};
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.Ed
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.Pp
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When
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.Dv enableComp
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is set to zero, all packets received on the
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.Dv ip
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hook are forwarded unchanged out the
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.Dv vjip
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hook.
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Similarly, when
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.Dv enableDecomp
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is set to zero, all packets received on the
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.Dv vjip
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hook are forwarded unchanged out the
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.Dv ip
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hook, and packets are not accepted on the
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.Dv vjcomp
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and
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.Dv vjuncomp
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hooks.
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When a node is first created,
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both compression and decompression are disabled and the node is
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therefore operating in bi-directional
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.Dq pass through
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mode.
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.Pp
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When enabling compression,
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.Dv maxChannel
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should be set to the number of outgoing compression channels minus one,
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and is a value between 3 and 15, inclusive.
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The
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.Dv compressCID
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field indicates whether it is OK to compress the CID header field for
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outgoing compressed TCP packets.
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This value should be zero unless
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either (a) it is not possible for an outgoing frame to be lost, or
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(b) lost frames can be reliably detected and immediately
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reported to the peer's decompression engine (see
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.Dv NGM_VJC_RECV_ERROR
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below).
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.It Dv NGM_VJC_GET_STATE
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This command returns the node's current state described by the
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.Dv "struct slcompress"
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structure, which is defined in
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.In net/slcompress.h .
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.It Dv NGM_VJC_CLR_STATS
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Clears the node statistics counters.
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Statistics are also cleared whenever the
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.Dv enableComp
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or
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.Dv enableDecomp
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fields are changed from zero to one by a
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.Dv NGM_VJC_SET_CONFIG
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control message.
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.It Dv NGM_VJC_RECV_ERROR
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When the peer has CID header field compression enabled,
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this message must be sent to the local
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.Nm vjc
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node immediately
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after detecting that a received frame has been lost, due to a bad
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checksum or for any other reason.
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Failing to do this can result in corrupted TCP stream data.
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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 BUGS
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As the initialization routine in the kernel implementation of
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Van Jacobson compression initializes both compression and decompression
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at once, this node does not allow compression and decompression to
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be enabled in separate operations.
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In order to enable one when
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the other is already enabled, first both must be disabled, then
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both enabled.
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This of course resets the node state.
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This restriction may be lifted in a later version.
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.Pp
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When built as a loadable kernel module, this module includes the file
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.Pa net/slcompress.c .
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Although loading the module should fail if
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.Pa net/slcompress.c
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already exists in the kernel, currently it does not, and the duplicate
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copies of the file do not interfere.
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However, this may change in the future.
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.Sh SEE ALSO
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.Xr netgraph 4 ,
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.Xr ng_iface 4 ,
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.Xr ng_ppp 4 ,
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.Xr ngctl 8
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.Rs
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.%A V. Jacobson
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.%T "Compressing TCP/IP Headers"
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.%O RFC 1144
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.Re
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.Rs
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.%A G. McGregor
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.%T "The PPP Internet Control Protocol (IPCP)"
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.%O RFC 1332
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.Re
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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 4.0 .
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.Sh AUTHORS
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.An Archie Cobbs Aq archie@FreeBSD.org
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