xref: /freebsd/contrib/libpcap/pcap-common.c (revision afdbf109c6a661a729938f68211054a0a50d38ac)

/*
 * Copyright (c) 1993, 1994, 1995, 1996, 1997
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that: (1) source code distributions
 * retain the above copyright notice and this paragraph in its entirety, (2)
 * distributions including binary code include the above copyright notice and
 * this paragraph in its entirety in the documentation or other materials
 * provided with the distribution, and (3) all advertising materials mentioning
 * features or use of this software display the following acknowledgement:
 * ``This product includes software developed by the University of California,
 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
 * the University nor the names of its contributors may be used to endorse
 * or promote products derived from this software without specific prior
 * written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * pcap-common.c - common code for pcap and pcapng files
 */

#include <config.h>

#include <pcap-types.h>

#include "pcap-int.h"

#include "pcap-common.h"

/*
 * We don't write DLT_* values to capture files, because they're not the
 * same on all platforms.
 *
 * Unfortunately, the various flavors of BSD have not always used the same
 * numerical values for the same data types, and various patches to
 * libpcap for non-BSD OSes have added their own DLT_* codes for link
 * layer encapsulation types seen on those OSes, and those codes have had,
 * in some cases, values that were also used, on other platforms, for other
 * link layer encapsulation types.
 *
 * This means that capture files of a type whose numerical DLT_* code
 * means different things on different BSDs, or with different versions
 * of libpcap, can't always be read on systems other than those like
 * the one running on the machine on which the capture was made.
 *
 * Instead, we define here a set of LINKTYPE_* codes, and map DLT_* codes
 * to LINKTYPE_* codes when writing a savefile header, and map LINKTYPE_*
 * codes to DLT_* codes when reading a savefile header.
 *
 * For those DLT_* codes that have, as far as we know, the same values on
 * all platforms (DLT_NULL through DLT_FDDI), we define LINKTYPE_xxx as
 * DLT_xxx; that way, captures of those types can still be read by
 * versions of libpcap that map LINKTYPE_* values to DLT_* values, and
 * captures of those types written by versions of libpcap that map DLT_
 * values to LINKTYPE_ values can still be read by older versions
 * of libpcap.
 *
 * The other LINKTYPE_* codes are given values starting at 100, in the
 * hopes that no DLT_* code will be given one of those values.
 *
 * In order to ensure that a given LINKTYPE_* code's value will refer to
 * the same encapsulation type on all platforms, you should not allocate
 * a new LINKTYPE_* value without consulting
 * "tcpdump-workers@lists.tcpdump.org".  The tcpdump developers will
 * allocate a value for you, and will not subsequently allocate it to
 * anybody else; that value will be added to the "pcap.h" in the
 * tcpdump.org Git repository, so that a future libpcap release will
 * include it.
 *
 * You should, if possible, also contribute patches to libpcap and tcpdump
 * to handle the new encapsulation type, so that they can also be checked
 * into the tcpdump.org Git repository and so that they will appear in
 * future libpcap and tcpdump releases.
 *
 * Do *NOT* assume that any values after the largest value in this file
 * are available; you might not have the most up-to-date version of this
 * file, and new values after that one might have been assigned.  Also,
 * do *NOT* use any values below 100 - those might already have been
 * taken by one (or more!) organizations.
 *
 * Any platform that defines additional DLT_* codes should:
 *
 *	request a LINKTYPE_* code and value from tcpdump.org,
 *	as per the above;
 *
 *	add, in their version of libpcap, an entry to map
 *	those DLT_* codes to the corresponding LINKTYPE_*
 *	code;
 *
 *	redefine, in their "net/bpf.h", any DLT_* values
 *	that collide with the values used by their additional
 *	DLT_* codes, to remove those collisions (but without
 *	making them collide with any of the LINKTYPE_*
 *	values equal to 50 or above; they should also avoid
 *	defining DLT_* values that collide with those
 *	LINKTYPE_* values, either).
 */

/*
 * These values the DLT_ values for which are the same on all platforms,
 * and that have been defined by <net/bpf.h> for ages.
 *
 * For those, the LINKTYPE_ values are equal to the DLT_ values.
 *
 * LINKTYPE_LOW_MATCHING_MIN is the lowest such value;
 * LINKTYPE_LOW_MATCHING_MAX is the highest such value.
 */
#define LINKTYPE_LOW_MATCHING_MIN	0		/* lowest value in this "matching" range */
#define LINKTYPE_NULL		DLT_NULL
#define LINKTYPE_ETHERNET	DLT_EN10MB	/* also for 100Mb and up */
#define LINKTYPE_EXP_ETHERNET	DLT_EN3MB	/* 3Mb experimental Ethernet */
#define LINKTYPE_AX25		DLT_AX25
#define LINKTYPE_PRONET		DLT_PRONET
#define LINKTYPE_CHAOS		DLT_CHAOS
#define LINKTYPE_IEEE802_5	DLT_IEEE802	/* DLT_IEEE802 is used for 802.5 Token Ring */
#define LINKTYPE_ARCNET_BSD	DLT_ARCNET	/* BSD-style headers */
#define LINKTYPE_SLIP		DLT_SLIP
#define LINKTYPE_PPP		DLT_PPP
#define LINKTYPE_FDDI		DLT_FDDI

#define LINKTYPE_LOW_MATCHING_MAX	LINKTYPE_FDDI	/* highest value in this "matching" range */

/*
 * LINKTYPE_PPP is for use when there might, or might not, be an RFC 1662
 * PPP in HDLC-like framing header (with 0xff 0x03 before the PPP protocol
 * field) at the beginning of the packet.
 *
 * This is for use when there is always such a header; the address field
 * might be 0xff, for regular PPP, or it might be an address field for Cisco
 * point-to-point with HDLC framing as per section 4.3.1 of RFC 1547 ("Cisco
 * HDLC").  This is, for example, what you get with NetBSD's DLT_PPP_SERIAL.
 *
 * We give it the same value as NetBSD's DLT_PPP_SERIAL, in the hopes that
 * nobody else will choose a DLT_ value of 50, and so that DLT_PPP_SERIAL
 * captures will be written out with a link type that NetBSD's tcpdump
 * can read.
 */
#define LINKTYPE_PPP_HDLC	50		/* PPP in HDLC-like framing */

#define LINKTYPE_PPP_ETHER	51		/* NetBSD PPP-over-Ethernet */

#define LINKTYPE_SYMANTEC_FIREWALL 99		/* Symantec Enterprise Firewall */

/*
 * These correspond to DLT_s that have different values on different
 * platforms; we map between these values in capture files and
 * the DLT_ values as returned by pcap_datalink() and passed to
 * pcap_open_dead().
 */
#define LINKTYPE_ATM_RFC1483	100		/* LLC/SNAP-encapsulated ATM */
#define LINKTYPE_RAW		101		/* raw IP */
#define LINKTYPE_SLIP_BSDOS	102		/* BSD/OS SLIP BPF header */
#define LINKTYPE_PPP_BSDOS	103		/* BSD/OS PPP BPF header */

/*
 * Values starting with 104 are used for newly-assigned link-layer
 * header type values; for those link-layer header types, the DLT_
 * value returned by pcap_datalink() and passed to pcap_open_dead(),
 * and the LINKTYPE_ value that appears in capture files, are the
 * same.
 *
 * LINKTYPE_HIGH_MATCHING_MIN is the lowest such value;
 * LINKTYPE_HIGH_MATCHING_MAX is the highest such value.
 */
#define LINKTYPE_HIGH_MATCHING_MIN	104		/* lowest value in the "matching" range */

#define LINKTYPE_C_HDLC		104		/* Cisco HDLC */
#define LINKTYPE_IEEE802_11	105		/* IEEE 802.11 (wireless) */
#define LINKTYPE_ATM_CLIP	106		/* Linux Classical IP over ATM */
#define LINKTYPE_FRELAY		107		/* Frame Relay */
#define LINKTYPE_LOOP		108		/* OpenBSD loopback */
#define LINKTYPE_ENC		109		/* OpenBSD IPSEC enc */

/*
 * These two types are reserved for future use.
 */
#define LINKTYPE_LANE8023	110		/* ATM LANE + 802.3 */
#define LINKTYPE_HIPPI		111		/* NetBSD HIPPI */

/*
 * Used for NetBSD DLT_HDLC; from looking at the one driver in NetBSD
 * that uses it, it's Cisco HDLC, so it's the same as DLT_C_HDLC/
 * LINKTYPE_C_HDLC, but we define a separate value to avoid some
 * compatibility issues with programs on NetBSD.
 *
 * All code should treat LINKTYPE_NETBSD_HDLC and LINKTYPE_C_HDLC the same.
 */
#define LINKTYPE_NETBSD_HDLC	112		/* NetBSD HDLC framing */

#define LINKTYPE_LINUX_SLL	113		/* Linux cooked socket capture */
#define LINKTYPE_LTALK		114		/* Apple LocalTalk hardware */
#define LINKTYPE_ECONET		115		/* Acorn Econet */

/*
 * Reserved for use with OpenBSD ipfilter.
 */
#define LINKTYPE_IPFILTER	116

#define LINKTYPE_PFLOG		117		/* OpenBSD DLT_PFLOG */
#define LINKTYPE_CISCO_IOS	118		/* For Cisco-internal use */
#define LINKTYPE_IEEE802_11_PRISM 119		/* 802.11 plus Prism II monitor mode radio metadata header */
#define LINKTYPE_IEEE802_11_AIRONET 120		/* 802.11 plus FreeBSD Aironet driver radio metadata header */

/*
 * Reserved for Siemens HiPath HDLC.
 */
#define LINKTYPE_HHDLC		121

#define LINKTYPE_IP_OVER_FC	122		/* RFC 2625 IP-over-Fibre Channel */
#define LINKTYPE_SUNATM		123		/* Solaris+SunATM */

/*
 * Reserved as per request from Kent Dahlgren <kent@praesum.com>
 * for private use.
 */
#define LINKTYPE_RIO		124		/* RapidIO */
#define LINKTYPE_PCI_EXP	125		/* PCI Express */
#define LINKTYPE_AURORA		126		/* Xilinx Aurora link layer */

#define LINKTYPE_IEEE802_11_RADIOTAP 127	/* 802.11 plus radiotap radio metadata header */

/*
 * Reserved for the TZSP encapsulation, as per request from
 * Chris Waters <chris.waters@networkchemistry.com>
 * TZSP is a generic encapsulation for any other link type,
 * which includes a means to include meta-information
 * with the packet, e.g. signal strength and channel
 * for 802.11 packets.
 */
#define LINKTYPE_TZSP		128		/* Tazmen Sniffer Protocol */

#define LINKTYPE_ARCNET_LINUX	129		/* Linux-style headers */

/*
 * Juniper-private data link types, as per request from
 * Hannes Gredler <hannes@juniper.net>.  The corresponding
 * DLT_s are used for passing on chassis-internal
 * metainformation such as QOS profiles, etc..
 */
#define LINKTYPE_JUNIPER_MLPPP  130
#define LINKTYPE_JUNIPER_MLFR   131
#define LINKTYPE_JUNIPER_ES     132
#define LINKTYPE_JUNIPER_GGSN   133
#define LINKTYPE_JUNIPER_MFR    134
#define LINKTYPE_JUNIPER_ATM2   135
#define LINKTYPE_JUNIPER_SERVICES 136
#define LINKTYPE_JUNIPER_ATM1   137

#define LINKTYPE_APPLE_IP_OVER_IEEE1394 138	/* Apple IP-over-IEEE 1394 cooked header */

#define LINKTYPE_MTP2_WITH_PHDR	139
#define LINKTYPE_MTP2		140
#define LINKTYPE_MTP3		141
#define LINKTYPE_SCCP		142

#define LINKTYPE_DOCSIS		143		/* DOCSIS MAC frames */

#define LINKTYPE_LINUX_IRDA	144		/* Linux-IrDA */

/*
 * Reserved for IBM SP switch and IBM Next Federation switch.
 */
#define LINKTYPE_IBM_SP		145
#define LINKTYPE_IBM_SN		146

/*
 * Reserved for private use.  If you have some link-layer header type
 * that you want to use within your organization, with the capture files
 * using that link-layer header type not ever be sent outside your
 * organization, you can use these values.
 *
 * No libpcap release will use these for any purpose, nor will any
 * tcpdump release use them, either.
 *
 * Do *NOT* use these in capture files that you expect anybody not using
 * your private versions of capture-file-reading tools to read; in
 * particular, do *NOT* use them in products, otherwise you may find that
 * people won't be able to use tcpdump, or snort, or Ethereal, or... to
 * read capture files from your firewall/intrusion detection/traffic
 * monitoring/etc. appliance, or whatever product uses that LINKTYPE_ value,
 * and you may also find that the developers of those applications will
 * not accept patches to let them read those files.
 *
 * Also, do not use them if somebody might send you a capture using them
 * for *their* private type and tools using them for *your* private type
 * would have to read them.
 *
 * Instead, in those cases, ask "tcpdump-workers@lists.tcpdump.org" for a
 * new DLT_ and LINKTYPE_ value, as per the comment in pcap/bpf.h, and use
 * the type you're given.
 */
#define LINKTYPE_USER0		147
#define LINKTYPE_USER1		148
#define LINKTYPE_USER2		149
#define LINKTYPE_USER3		150
#define LINKTYPE_USER4		151
#define LINKTYPE_USER5		152
#define LINKTYPE_USER6		153
#define LINKTYPE_USER7		154
#define LINKTYPE_USER8		155
#define LINKTYPE_USER9		156
#define LINKTYPE_USER10		157
#define LINKTYPE_USER11		158
#define LINKTYPE_USER12		159
#define LINKTYPE_USER13		160
#define LINKTYPE_USER14		161
#define LINKTYPE_USER15		162

/*
 * For future use with 802.11 captures - defined by AbsoluteValue
 * Systems to store a number of bits of link-layer information
 * including radio information:
 *
 *	http://www.shaftnet.org/~pizza/software/capturefrm.txt
 */
#define LINKTYPE_IEEE802_11_AVS	163	/* 802.11 plus AVS radio metadata header */

/*
 * Juniper-private data link type, as per request from
 * Hannes Gredler <hannes@juniper.net>.  The corresponding
 * DLT_s are used for passing on chassis-internal
 * metainformation such as QOS profiles, etc..
 */
#define LINKTYPE_JUNIPER_MONITOR 164

/*
 * BACnet MS/TP frames.
 */
#define LINKTYPE_BACNET_MS_TP	165

/*
 * Another PPP variant as per request from Karsten Keil <kkeil@suse.de>.
 *
 * This is used in some OSes to allow a kernel socket filter to distinguish
 * between incoming and outgoing packets, on a socket intended to
 * supply pppd with outgoing packets so it can do dial-on-demand and
 * hangup-on-lack-of-demand; incoming packets are filtered out so they
 * don't cause pppd to hold the connection up (you don't want random
 * input packets such as port scans, packets from old lost connections,
 * etc. to force the connection to stay up).
 *
 * The first byte of the PPP header (0xff03) is modified to accommodate
 * the direction - 0x00 = IN, 0x01 = OUT.
 */
#define LINKTYPE_PPP_PPPD	166

/*
 * Juniper-private data link type, as per request from
 * Hannes Gredler <hannes@juniper.net>.  The DLT_s are used
 * for passing on chassis-internal metainformation such as
 * QOS profiles, cookies, etc..
 */
#define LINKTYPE_JUNIPER_PPPOE     167
#define LINKTYPE_JUNIPER_PPPOE_ATM 168

#define LINKTYPE_GPRS_LLC	169		/* GPRS LLC */
#define LINKTYPE_GPF_T		170		/* GPF-T (ITU-T G.7041/Y.1303) */
#define LINKTYPE_GPF_F		171		/* GPF-F (ITU-T G.7041/Y.1303) */

/*
 * Requested by Oolan Zimmer <oz@gcom.com> for use in Gcom's T1/E1 line
 * monitoring equipment.
 */
#define LINKTYPE_GCOM_T1E1	172
#define LINKTYPE_GCOM_SERIAL	173

/*
 * Juniper-private data link type, as per request from
 * Hannes Gredler <hannes@juniper.net>.  The DLT_ is used
 * for internal communication to Physical Interface Cards (PIC)
 */
#define LINKTYPE_JUNIPER_PIC_PEER    174

/*
 * Link types requested by Gregor Maier <gregor@endace.com> of Endace
 * Measurement Systems.  They add an ERF header (see
 * https://www.endace.com/support/EndaceRecordFormat.pdf) in front of
 * the link-layer header.
 */
#define LINKTYPE_ERF_ETH	175	/* Ethernet */
#define LINKTYPE_ERF_POS	176	/* Packet-over-SONET */

/*
 * Requested by Daniele Orlandi <daniele@orlandi.com> for raw LAPD
 * for vISDN (http://www.orlandi.com/visdn/).  Its link-layer header
 * includes additional information before the LAPD header, so it's
 * not necessarily a generic LAPD header.
 */
#define LINKTYPE_LINUX_LAPD	177

/*
 * Juniper-private data link type, as per request from
 * Hannes Gredler <hannes@juniper.net>.
 * The Link Types are used for prepending meta-information
 * like interface index, interface name
 * before standard Ethernet, PPP, Frelay & C-HDLC Frames
 */
#define LINKTYPE_JUNIPER_ETHER  178
#define LINKTYPE_JUNIPER_PPP    179
#define LINKTYPE_JUNIPER_FRELAY 180
#define LINKTYPE_JUNIPER_CHDLC  181

/*
 * Multi Link Frame Relay (FRF.16)
 */
#define LINKTYPE_MFR            182

/*
 * Juniper-private data link type, as per request from
 * Hannes Gredler <hannes@juniper.net>.
 * The DLT_ is used for internal communication with a
 * voice Adapter Card (PIC)
 */
#define LINKTYPE_JUNIPER_VP     183

/*
 * Arinc 429 frames.
 * DLT_ requested by Gianluca Varenni <gianluca.varenni@cacetech.com>.
 * Every frame contains a 32bit A429 label.
 * More documentation on Arinc 429 can be found at
 * https://web.archive.org/web/20040616233302/https://www.condoreng.com/support/downloads/tutorials/ARINCTutorial.pdf
 */
#define LINKTYPE_A429           184

/*
 * Arinc 653 Interpartition Communication messages.
 * DLT_ requested by Gianluca Varenni <gianluca.varenni@cacetech.com>.
 * Please refer to the A653-1 standard for more information.
 */
#define LINKTYPE_A653_ICM       185

/*
 * This used to be "USB packets, beginning with a USB setup header;
 * requested by Paolo Abeni <paolo.abeni@email.it>."
 *
 * However, that header didn't work all that well - it left out some
 * useful information - and was abandoned in favor of the DLT_USB_LINUX
 * header.
 *
 * This is now used by FreeBSD for its BPF taps for USB; that has its
 * own headers.  So it is written, so it is done.
 */
#define LINKTYPE_USB_FREEBSD	186

/*
 * Bluetooth HCI UART transport layer (part H:4); requested by
 * Paolo Abeni.
 */
#define LINKTYPE_BLUETOOTH_HCI_H4	187

/*
 * IEEE 802.16 MAC Common Part Sublayer; requested by Maria Cruz
 * <cruz_petagay@bah.com>.
 */
#define LINKTYPE_IEEE802_16_MAC_CPS	188

/*
 * USB packets, beginning with a Linux USB header; requested by
 * Paolo Abeni <paolo.abeni@email.it>.
 */
#define LINKTYPE_USB_LINUX		189

/*
 * Controller Area Network (CAN) v. 2.0B packets.
 * DLT_ requested by Gianluca Varenni <gianluca.varenni@cacetech.com>.
 * Used to dump CAN packets coming from a CAN Vector board.
 * More documentation on the CAN v2.0B frames can be found at
 * http://www.can-cia.org/downloads/?269
 */
#define LINKTYPE_CAN20B         190

/*
 * IEEE 802.15.4, with address fields padded, as is done by Linux
 * drivers; requested by Juergen Schimmer.
 */
#define LINKTYPE_IEEE802_15_4_LINUX	191

/*
 * Per Packet Information encapsulated packets.
 * LINKTYPE_ requested by Gianluca Varenni <gianluca.varenni@cacetech.com>.
 */
#define LINKTYPE_PPI			192

/*
 * Header for 802.16 MAC Common Part Sublayer plus a radiotap radio header;
 * requested by Charles Clancy.
 */
#define LINKTYPE_IEEE802_16_MAC_CPS_RADIO	193

/*
 * Juniper-private data link type, as per request from
 * Hannes Gredler <hannes@juniper.net>.
 * The DLT_ is used for internal communication with a
 * integrated service module (ISM).
 */
#define LINKTYPE_JUNIPER_ISM    194

/*
 * IEEE 802.15.4, exactly as it appears in the spec (no padding, no
 * nothing), and with the FCS at the end of the frame; requested by
 * Mikko Saarnivala <mikko.saarnivala@sensinode.com>.
 *
 * This should only be used if the FCS is present at the end of the
 * frame; if the frame has no FCS, DLT_IEEE802_15_4_NOFCS should be
 * used.
 */
#define LINKTYPE_IEEE802_15_4_WITHFCS	195

/*
 * Various link-layer types, with a pseudo-header, for SITA
 * (https://www.sita.aero/); requested by Fulko Hew (fulko.hew@gmail.com).
 */
#define LINKTYPE_SITA		196

/*
 * Various link-layer types, with a pseudo-header, for Endace DAG cards;
 * encapsulates Endace ERF records.  Requested by Stephen Donnelly
 * <stephen@endace.com>.
 */
#define LINKTYPE_ERF		197

/*
 * Special header prepended to Ethernet packets when capturing from a
 * u10 Networks board.  Requested by Phil Mulholland
 * <phil@u10networks.com>.
 */
#define LINKTYPE_RAIF1		198

/*
 * IPMB packet for IPMI, beginning with a 2-byte header, followed by
 * the I2C slave address, followed by the netFn and LUN, etc..
 * Requested by Chanthy Toeung <chanthy.toeung@ca.kontron.com>.
 *
 * XXX - its DLT_ value used to be called DLT_IPMB, back when we got the
 * impression from the email thread requesting it that the packet
 * had no extra 2-byte header.  We've renamed it; if anybody used
 * DLT_IPMB and assumed no 2-byte header, this will cause the compile
 * to fail, at which point we'll have to figure out what to do about
 * the two header types using the same DLT_/LINKTYPE_ value.  If that
 * doesn't happen, we'll assume nobody used it and that the redefinition
 * is safe.
 */
#define LINKTYPE_IPMB_KONTRON	199

/*
 * Juniper-private data link type, as per request from
 * Hannes Gredler <hannes@juniper.net>.
 * The DLT_ is used for capturing data on a secure tunnel interface.
 */
#define LINKTYPE_JUNIPER_ST     200

/*
 * Bluetooth HCI UART transport layer (part H:4), with pseudo-header
 * that includes direction information; requested by Paolo Abeni.
 */
#define LINKTYPE_BLUETOOTH_HCI_H4_WITH_PHDR	201

/*
 * AX.25 packet with a 1-byte KISS header; see
 *
 *	http://www.ax25.net/kiss.htm
 *
 * as per Richard Stearn <richard@rns-stearn.demon.co.uk>.
 */
#define LINKTYPE_AX25_KISS	202

/*
 * LAPD packets from an ISDN channel, starting with the address field,
 * with no pseudo-header.
 * Requested by Varuna De Silva <varunax@gmail.com>.
 */
#define LINKTYPE_LAPD		203

/*
 * PPP, with a one-byte direction pseudo-header prepended - zero means
 * "received by this host", non-zero (any non-zero value) means "sent by
 * this host" - as per Will Barker <w.barker@zen.co.uk>.
 */
#define LINKTYPE_PPP_WITH_DIR	204	/* Don't confuse with LINKTYPE_PPP_PPPD */

/*
 * Cisco HDLC, with a one-byte direction pseudo-header prepended - zero
 * means "received by this host", non-zero (any non-zero value) means
 * "sent by this host" - as per Will Barker <w.barker@zen.co.uk>.
 */
#define LINKTYPE_C_HDLC_WITH_DIR 205	/* Cisco HDLC */

/*
 * Frame Relay, with a one-byte direction pseudo-header prepended - zero
 * means "received by this host" (DCE -> DTE), non-zero (any non-zero
 * value) means "sent by this host" (DTE -> DCE) - as per Will Barker
 * <w.barker@zen.co.uk>.
 */
#define LINKTYPE_FRELAY_WITH_DIR 206	/* Frame Relay */

/*
 * LAPB, with a one-byte direction pseudo-header prepended - zero means
 * "received by this host" (DCE -> DTE), non-zero (any non-zero value)
 * means "sent by this host" (DTE -> DCE)- as per Will Barker
 * <w.barker@zen.co.uk>.
 */
#define LINKTYPE_LAPB_WITH_DIR	207	/* LAPB */

/*
 * 208 is reserved for an as-yet-unspecified proprietary link-layer
 * type, as requested by Will Barker.
 */

/*
 * IPMB with a Linux-specific pseudo-header; as requested by Alexey Neyman
 * <avn@pigeonpoint.com>.
 */
#define LINKTYPE_IPMB_LINUX	209

/*
 * FlexRay automotive bus - http://www.flexray.com/ - as requested
 * by Hannes Kaelber <hannes.kaelber@x2e.de>.
 */
#define LINKTYPE_FLEXRAY	210

/*
 * Media Oriented Systems Transport (MOST) bus for multimedia
 * transport - https://www.mostcooperation.com/ - as requested
 * by Hannes Kaelber <hannes.kaelber@x2e.de>.
 */
#define LINKTYPE_MOST		211

/*
 * Local Interconnect Network (LIN) bus for vehicle networks -
 * http://www.lin-subbus.org/ - as requested by Hannes Kaelber
 * <hannes.kaelber@x2e.de>.
 */
#define LINKTYPE_LIN		212

/*
 * X2E-private data link type used for serial line capture,
 * as requested by Hannes Kaelber <hannes.kaelber@x2e.de>.
 */
#define LINKTYPE_X2E_SERIAL	213

/*
 * X2E-private data link type used for the Xoraya data logger
 * family, as requested by Hannes Kaelber <hannes.kaelber@x2e.de>.
 */
#define LINKTYPE_X2E_XORAYA	214

/*
 * IEEE 802.15.4, exactly as it appears in the spec (no padding, no
 * nothing), but with the PHY-level data for non-ASK PHYs (4 octets
 * of 0 as preamble, one octet of SFD, one octet of frame length+
 * reserved bit, and then the MAC-layer data, starting with the
 * frame control field).
 *
 * Requested by Max Filippov <jcmvbkbc@gmail.com>.
 */
#define LINKTYPE_IEEE802_15_4_NONASK_PHY	215

/*
 * David Gibson <david@gibson.dropbear.id.au> requested this for
 * captures from the Linux kernel /dev/input/eventN devices. This
 * is used to communicate keystrokes and mouse movements from the
 * Linux kernel to display systems, such as Xorg.
 */
#define LINKTYPE_LINUX_EVDEV	216

/*
 * GSM Um and Abis interfaces, preceded by a "gsmtap" header.
 *
 * Requested by Harald Welte <laforge@gnumonks.org>.
 */
#define LINKTYPE_GSMTAP_UM	217
#define LINKTYPE_GSMTAP_ABIS	218

/*
 * MPLS, with an MPLS label as the link-layer header.
 * Requested by Michele Marchetto <michele@openbsd.org> on behalf
 * of OpenBSD.
 */
#define LINKTYPE_MPLS		219

/*
 * USB packets, beginning with a Linux USB header, with the USB header
 * padded to 64 bytes; required for memory-mapped access.
 */
#define LINKTYPE_USB_LINUX_MMAPPED		220

/*
 * DECT packets, with a pseudo-header; requested by
 * Matthias Wenzel <tcpdump@mazzoo.de>.
 */
#define LINKTYPE_DECT		221

/*
 * From: "Lidwa, Eric (GSFC-582.0)[SGT INC]" <eric.lidwa-1@nasa.gov>
 * Date: Mon, 11 May 2009 11:18:30 -0500
 *
 * DLT_AOS. We need it for AOS Space Data Link Protocol.
 *   I have already written dissectors for but need an OK from
 *   legal before I can submit a patch.
 *
 */
#define LINKTYPE_AOS		222

/*
 * WirelessHART (Highway Addressable Remote Transducer)
 * From the HART Communication Foundation
 * IEC/PAS 62591
 *
 * Requested by Sam Roberts <vieuxtech@gmail.com>.
 */
#define LINKTYPE_WIHART		223

/*
 * Fibre Channel FC-2 frames, beginning with a Frame_Header.
 * Requested by Kahou Lei <kahou82@gmail.com>.
 */
#define LINKTYPE_FC_2		224

/*
 * Fibre Channel FC-2 frames, beginning with an encoding of the
 * SOF, and ending with an encoding of the EOF.
 *
 * The encodings represent the frame delimiters as 4-byte sequences
 * representing the corresponding ordered sets, with K28.5
 * represented as 0xBC, and the D symbols as the corresponding
 * byte values; for example, SOFi2, which is K28.5 - D21.5 - D1.2 - D21.2,
 * is represented as 0xBC 0xB5 0x55 0x55.
 *
 * Requested by Kahou Lei <kahou82@gmail.com>.
 */
#define LINKTYPE_FC_2_WITH_FRAME_DELIMS		225

/*
 * Solaris ipnet pseudo-header; requested by Darren Reed <Darren.Reed@Sun.COM>.
 *
 * The pseudo-header starts with a one-byte version number; for version 2,
 * the pseudo-header is:
 *
 * struct dl_ipnetinfo {
 *     uint8_t   dli_version;
 *     uint8_t   dli_family;
 *     uint16_t  dli_htype;
 *     uint32_t  dli_pktlen;
 *     uint32_t  dli_ifindex;
 *     uint32_t  dli_grifindex;
 *     uint32_t  dli_zsrc;
 *     uint32_t  dli_zdst;
 * };
 *
 * dli_version is 2 for the current version of the pseudo-header.
 *
 * dli_family is a Solaris address family value, so it's 2 for IPv4
 * and 26 for IPv6.
 *
 * dli_htype is a "hook type" - 0 for incoming packets, 1 for outgoing
 * packets, and 2 for packets arriving from another zone on the same
 * machine.
 *
 * dli_pktlen is the length of the packet data following the pseudo-header
 * (so the captured length minus dli_pktlen is the length of the
 * pseudo-header, assuming the entire pseudo-header was captured).
 *
 * dli_ifindex is the interface index of the interface on which the
 * packet arrived.
 *
 * dli_grifindex is the group interface index number (for IPMP interfaces).
 *
 * dli_zsrc is the zone identifier for the source of the packet.
 *
 * dli_zdst is the zone identifier for the destination of the packet.
 *
 * A zone number of 0 is the global zone; a zone number of 0xffffffff
 * means that the packet arrived from another host on the network, not
 * from another zone on the same machine.
 *
 * An IPv4 or IPv6 datagram follows the pseudo-header; dli_family indicates
 * which of those it is.
 */
#define LINKTYPE_IPNET		226

/*
 * CAN (Controller Area Network) frames, with a pseudo-header as supplied
 * by Linux SocketCAN, and with multi-byte numerical fields in that header
 * in big-endian byte order.
 *
 * See Documentation/networking/can.txt in the Linux source.
 *
 * Requested by Felix Obenhuber <felix@obenhuber.de>.
 */
#define LINKTYPE_CAN_SOCKETCAN	227

/*
 * Raw IPv4/IPv6; different from DLT_RAW in that the DLT_ value specifies
 * whether it's v4 or v6.  Requested by Darren Reed <Darren.Reed@Sun.COM>.
 */
#define LINKTYPE_IPV4		228
#define LINKTYPE_IPV6		229

/*
 * IEEE 802.15.4, exactly as it appears in the spec (no padding, no
 * nothing), and with no FCS at the end of the frame; requested by
 * Jon Smirl <jonsmirl@gmail.com>.
 */
#define LINKTYPE_IEEE802_15_4_NOFCS		230

/*
 * Raw D-Bus:
 *
 *	https://www.freedesktop.org/wiki/Software/dbus
 *
 * messages:
 *
 *	https://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-messages
 *
 * starting with the endianness flag, followed by the message type, etc.,
 * but without the authentication handshake before the message sequence:
 *
 *	https://dbus.freedesktop.org/doc/dbus-specification.html#auth-protocol
 *
 * Requested by Martin Vidner <martin@vidner.net>.
 */
#define LINKTYPE_DBUS		231

/*
 * Juniper-private data link type, as per request from
 * Hannes Gredler <hannes@juniper.net>.
 */
#define LINKTYPE_JUNIPER_VS			232
#define LINKTYPE_JUNIPER_SRX_E2E		233
#define LINKTYPE_JUNIPER_FIBRECHANNEL		234

/*
 * DVB-CI (DVB Common Interface for communication between a PC Card
 * module and a DVB receiver).  See
 *
 *	https://www.kaiser.cx/pcap-dvbci.html
 *
 * for the specification.
 *
 * Requested by Martin Kaiser <martin@kaiser.cx>.
 */
#define LINKTYPE_DVB_CI		235

/*
 * Variant of 3GPP TS 27.010 multiplexing protocol.  Requested
 * by Hans-Christoph Schemmel <hans-christoph.schemmel@cinterion.com>.
 */
#define LINKTYPE_MUX27010	236

/*
 * STANAG 5066 D_PDUs.  Requested by M. Baris Demiray
 * <barisdemiray@gmail.com>.
 */
#define LINKTYPE_STANAG_5066_D_PDU		237

/*
 * Juniper-private data link type, as per request from
 * Hannes Gredler <hannes@juniper.net>.
 */
#define LINKTYPE_JUNIPER_ATM_CEMIC		238

/*
 * NetFilter LOG messages
 * (payload of netlink NFNL_SUBSYS_ULOG/NFULNL_MSG_PACKET packets)
 *
 * Requested by Jakub Zawadzki <darkjames-ws@darkjames.pl>
 */
#define LINKTYPE_NFLOG		239

/*
 * Hilscher Gesellschaft fuer Systemautomation mbH link-layer type
 * for Ethernet packets with a 4-byte pseudo-header and always
 * with the payload including the FCS, as supplied by their
 * netANALYZER hardware and software.
 *
 * Requested by Holger P. Frommer <HPfrommer@hilscher.com>
 */
#define LINKTYPE_NETANALYZER	240

/*
 * Hilscher Gesellschaft fuer Systemautomation mbH link-layer type
 * for Ethernet packets with a 4-byte pseudo-header and FCS and
 * 1 byte of SFD, as supplied by their netANALYZER hardware and
 * software.
 *
 * Requested by Holger P. Frommer <HPfrommer@hilscher.com>
 */
#define LINKTYPE_NETANALYZER_TRANSPARENT	241

/*
 * IP-over-InfiniBand, as specified by RFC 4391.
 *
 * Requested by Petr Sumbera <petr.sumbera@oracle.com>.
 */
#define LINKTYPE_IPOIB		242

/*
 * MPEG-2 transport stream (ISO 13818-1/ITU-T H.222.0).
 *
 * Requested by Guy Martin <gmsoft@tuxicoman.be>.
 */
#define LINKTYPE_MPEG_2_TS	243

/*
 * ng4T GmbH's UMTS Iub/Iur-over-ATM and Iub/Iur-over-IP format as
 * used by their ng40 protocol tester.
 *
 * Requested by Jens Grimmer <jens.grimmer@ng4t.com>.
 */
#define LINKTYPE_NG40		244

/*
 * Pseudo-header giving adapter number and flags, followed by an NFC
 * (Near-Field Communications) Logical Link Control Protocol (LLCP) PDU,
 * as specified by NFC Forum Logical Link Control Protocol Technical
 * Specification LLCP 1.1.
 *
 * Requested by Mike Wakerly <mikey@google.com>.
 */
#define LINKTYPE_NFC_LLCP	245

/*
 * pfsync output; DLT_PFSYNC is 18, which collides with DLT_CIP in
 * SuSE 6.3, on OpenBSD, NetBSD, DragonFly BSD, and macOS, and
 * is 121, which collides with DLT_HHDLC, in FreeBSD.  We pick a
 * shiny new link-layer header type value that doesn't collide with
 * anything, in the hopes that future pfsync savefiles, if any,
 * won't require special hacks to distinguish from other savefiles.
 */
#define LINKTYPE_PFSYNC		246

/*
 * Raw InfiniBand packets, starting with the Local Routing Header.
 *
 * Requested by Oren Kladnitsky <orenk@mellanox.com>.
 */
#define LINKTYPE_INFINIBAND	247

/*
 * SCTP, with no lower-level protocols (i.e., no IPv4 or IPv6).
 *
 * Requested by Michael Tuexen <Michael.Tuexen@lurchi.franken.de>.
 */
#define LINKTYPE_SCTP		248

/*
 * USB packets, beginning with a USBPcap header.
 *
 * Requested by Tomasz Mon <desowin@gmail.com>
 */
#define LINKTYPE_USBPCAP	249

/*
 * Schweitzer Engineering Laboratories "RTAC" product serial-line
 * packets.
 *
 * Requested by Chris Bontje <chris_bontje@selinc.com>.
 */
#define LINKTYPE_RTAC_SERIAL		250

/*
 * Bluetooth Low Energy air interface link-layer packets.
 *
 * Requested by Mike Kershaw <dragorn@kismetwireless.net>.
 */
#define LINKTYPE_BLUETOOTH_LE_LL	251

/*
 * Link-layer header type for upper-protocol layer PDU saves from wireshark.
 *
 * the actual contents are determined by two TAGs, one or more of
 * which is stored with each packet:
 *
 *   EXP_PDU_TAG_DISSECTOR_NAME      the name of the Wireshark dissector
 *				     that can make sense of the data stored.
 *
 *   EXP_PDU_TAG_HEUR_DISSECTOR_NAME the name of the Wireshark heuristic
 *				     dissector that can make sense of the
 *				     data stored.
 */
#define LINKTYPE_WIRESHARK_UPPER_PDU	252

/*
 * Link-layer header type for the netlink protocol (nlmon devices).
 */
#define LINKTYPE_NETLINK		253

/*
 * Bluetooth Linux Monitor headers for the BlueZ stack.
 */
#define LINKTYPE_BLUETOOTH_LINUX_MONITOR	254

/*
 * Bluetooth Basic Rate/Enhanced Data Rate baseband packets, as
 * captured by Ubertooth.
 */
#define LINKTYPE_BLUETOOTH_BREDR_BB	255

/*
 * Bluetooth Low Energy link layer packets, as captured by Ubertooth.
 */
#define LINKTYPE_BLUETOOTH_LE_LL_WITH_PHDR	256

/*
 * PROFIBUS data link layer.
 */
#define LINKTYPE_PROFIBUS_DL		257

/*
 * Apple's DLT_PKTAP headers.
 *
 * Sadly, the folks at Apple either had no clue that the DLT_USERn values
 * are for internal use within an organization and partners only, and
 * didn't know that the right way to get a link-layer header type is to
 * ask tcpdump.org for one, or knew and didn't care, so they just
 * used DLT_USER2, which causes problems for everything except for
 * their version of tcpdump.
 *
 * So I'll just give them one; hopefully this will show up in a
 * libpcap release in time for them to get this into 10.10 Big Sur
 * or whatever Mavericks' successor is called.  LINKTYPE_PKTAP
 * will be 258 *even on macOS*; that is *intentional*, so that
 * PKTAP files look the same on *all* OSes (different OSes can have
 * different numerical values for a given DLT_, but *MUST NOT* have
 * different values for what goes in a file, as files can be moved
 * between OSes!).
 */
#define LINKTYPE_PKTAP		258

/*
 * Ethernet packets preceded by a header giving the last 6 octets
 * of the preamble specified by 802.3-2012 Clause 65, section
 * 65.1.3.2 "Transmit".
 */
#define LINKTYPE_EPON		259

/*
 * IPMI trace packets, as specified by Table 3-20 "Trace Data Block Format"
 * in the PICMG HPM.2 specification.
 */
#define LINKTYPE_IPMI_HPM_2	260

/*
 * per  Joshua Wright <jwright@hasborg.com>, formats for Zwave captures.
 */
#define LINKTYPE_ZWAVE_R1_R2	261
#define LINKTYPE_ZWAVE_R3	262

/*
 * per Steve Karg <skarg@users.sourceforge.net>, formats for Wattstopper
 * Digital Lighting Management room bus serial protocol captures.
 */
#define LINKTYPE_WATTSTOPPER_DLM 263

/*
 * ISO 14443 contactless smart card messages.
 */
#define LINKTYPE_ISO_14443      264

/*
 * Radio data system (RDS) groups.  IEC 62106.
 * Per Jonathan Brucker <jonathan.brucke@gmail.com>.
 */
#define LINKTYPE_RDS		265

/*
 * USB packets, beginning with a Darwin (macOS, etc.) header.
 */
#define LINKTYPE_USB_DARWIN	266

/*
 * OpenBSD DLT_OPENFLOW.
 */
#define LINKTYPE_OPENFLOW	267

/*
 * SDLC frames containing SNA PDUs.
 */
#define LINKTYPE_SDLC		268

/*
 * per "Selvig, Bjorn" <b.selvig@ti.com> used for
 * TI protocol sniffer.
 */
#define LINKTYPE_TI_LLN_SNIFFER	269

/*
 * per: Erik de Jong <erikdejong at gmail.com> for
 *   https://github.com/eriknl/LoRaTap/releases/tag/v0.1
 */
#define LINKTYPE_LORATAP        270

/*
 * per: Stefanha at gmail.com for
 *   https://lists.sandelman.ca/pipermail/tcpdump-workers/2017-May/000772.html
 * and: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/vsockmon.h
 * for: https://qemu-project.org/Features/VirtioVsock
 */
#define LINKTYPE_VSOCK          271

/*
 * Nordic Semiconductor Bluetooth LE sniffer.
 */
#define LINKTYPE_NORDIC_BLE	272

/*
 * Excentis DOCSIS 3.1 RF sniffer (XRA-31)
 *   per: bruno.verstuyft at excentis.com
 *        https://www.xra31.com/xra-header
 */
#define LINKTYPE_DOCSIS31_XRA31	273

/*
 * mPackets, as specified by IEEE 802.3br Figure 99-4, starting
 * with the preamble and always ending with a CRC field.
 */
#define LINKTYPE_ETHERNET_MPACKET	274

/*
 * DisplayPort AUX channel monitoring data as specified by VESA
 * DisplayPort(DP) Standard preceded by a pseudo-header.
 *    per dirk.eibach at gdsys.cc
 */
#define LINKTYPE_DISPLAYPORT_AUX	275

/*
 * Linux cooked sockets v2.
 */
#define LINKTYPE_LINUX_SLL2	276

/*
 * Sercos Monitor, per Manuel Jacob <manuel.jacob at steinbeis-stg.de>
 */
#define LINKTYPE_SERCOS_MONITOR 277

/*
 * OpenVizsla http://openvizsla.org is open source USB analyzer hardware.
 * It consists of FPGA with attached USB phy and FTDI chip for streaming
 * the data to the host PC.
 *
 * Current OpenVizsla data encapsulation format is described here:
 * https://github.com/matwey/libopenvizsla/wiki/OpenVizsla-protocol-description
 *
 */
#define LINKTYPE_OPENVIZSLA     278

/*
 * The Elektrobit High Speed Capture and Replay (EBHSCR) protocol is produced
 * by a PCIe Card for interfacing high speed automotive interfaces.
 *
 * The specification for this frame format can be found at:
 *   https://www.elektrobit.com/ebhscr
 *
 * for Guenter.Ebermann at elektrobit.com
 *
 */
#define LINKTYPE_EBHSCR	        279

/*
 * The https://fd.io vpp graph dispatch tracer produces pcap trace files
 * in the format documented here:
 * https://fdio-vpp.readthedocs.io/en/latest/gettingstarted/developers/vnet.html#graph-dispatcher-pcap-tracing
 */
#define LINKTYPE_VPP_DISPATCH	280

/*
 * Broadcom Ethernet switches (ROBO switch) 4 bytes proprietary tagging format.
 */
#define LINKTYPE_DSA_TAG_BRCM	281
#define LINKTYPE_DSA_TAG_BRCM_PREPEND	282

/*
 * IEEE 802.15.4 with pseudo-header and optional meta-data TLVs, PHY payload
 * exactly as it appears in the spec (no padding, no nothing), and FCS if
 * specified by FCS Type TLV;  requested by James Ko <jck@exegin.com>.
 * Specification at https://github.com/jkcko/ieee802.15.4-tap
 */
#define LINKTYPE_IEEE802_15_4_TAP       283

/*
 * Marvell (Ethertype) Distributed Switch Architecture proprietary tagging format.
 */
#define LINKTYPE_DSA_TAG_DSA	284
#define LINKTYPE_DSA_TAG_EDSA	285

/*
 * Payload of lawful intercept packets using the ELEE protocol;
 * https://socket.hr/draft-dfranusic-opsawg-elee-00.xml
 * https://xml2rfc.tools.ietf.org/cgi-bin/xml2rfc.cgi?url=https://socket.hr/draft-dfranusic-opsawg-elee-00.xml&modeAsFormat=html/ascii
 */
#define LINKTYPE_ELEE		286

/*
 * Serial frames transmitted between a host and a Z-Wave chip.
 */
#define LINKTYPE_Z_WAVE_SERIAL	287

/*
 * USB 2.0, 1.1, and 1.0 packets as transmitted over the cable.
 */
#define LINKTYPE_USB_2_0	288

/*
 * ATSC Link-Layer Protocol (A/330) packets.
 */
#define LINKTYPE_ATSC_ALP	289

#define LINKTYPE_HIGH_MATCHING_MAX	289		/* highest value in the "matching" range */

/*
 * The DLT_ and LINKTYPE_ values in the "matching" range should be the
 * same, so DLT_HIGH_MATCHING_MAX and LINKTYPE_HIGH_MATCHING_MAX should be the
 * same.
 */
#if LINKTYPE_HIGH_MATCHING_MAX != DLT_HIGH_MATCHING_MAX
#error The LINKTYPE_ high matching range does not match the DLT_ matching range
#endif

/*
 * Map a DLT_* code to the corresponding LINKTYPE_* code.
 * Used to generate link-layer types written to savefiles.
 */
int
dlt_to_linktype(int dlt)
{
	/*
	 * All values in the low matching range were handed out before
	 * assigning DLT_* codes became a free-for-all, so they're the
	 * same on all platforms, and thus are given LINKTYPE_* codes
	 * with the same numerical values as the corresponding DLT_*
	 * code.
	 */
	if (dlt >= DLT_LOW_MATCHING_MIN && dlt <= DLT_LOW_MATCHING_MAX)
		return (dlt);

#if DLT_PFSYNC != LINKTYPE_PFSYNC
	/*
	 * DLT_PFSYNC has a code on several platforms that's in the
	 * non-matching range, a code on FreeBSD that's in the high
	 * matching range and that's *not* equal to LINKTYPE_PFSYNC,
	 * and has a code on the rmaining platforms that's equal
	 * to LINKTYPE_PFSYNC, which is in the high matching range.
	 *
	 * Map it to LINKTYPE_PFSYNC if it's not equal to LINKTYPE_PFSYNC.
	 */
	if (dlt == DLT_PFSYNC)
		return (LINKTYPE_PFSYNC);
#endif

	/*
	 * DLT_PKTAP is defined as DLT_USER2 - which is in the high
	 * matching range - on Darwin because Apple used DLT_USER2
	 * on systems that users ran, not just as an internal thing.
	 *
	 * We map it to LINKTYPE_PKTAP if it's not equal to LINKTYPE_PKTAP
	 * so that DLT_PKTAP captures from Apple machines can be read by
	 * software that either doesn't handle DLT_USER2 or that handles it
	 * as something other than Apple PKTAP.
	 */
#if DLT_PKTAP != LINKTYPE_PKTAP
	if (dlt == DLT_PKTAP)
		return (LINKTYPE_PKTAP);
#endif

	/*
	 * For all other DLT_* codes in the high matching range, the DLT
	 * code value is the same as the LINKTYPE_* code value.
	 */
	if (dlt >= DLT_HIGH_MATCHING_MIN && dlt <= DLT_HIGH_MATCHING_MAX)
		return (dlt);

	/*
	 * These DLT_* codes have different values on different
	 * platforms, so we assigned them LINKTYPE_* codes just
	 * below the lower bound of the high matchig range;
	 * those values should never be equal to any DLT_*
	 * code, so that should avoid collisions.
	 *
	 * That way, for example, "raw IP" packets will have
	 * LINKTYPE_RAW as the code in all savefiles for
	 * which the code that writes them maps to that
	 * value, regardless of the platform on which they
	 * were written, so they should be readable on all
	 * platforms without having to determine on which
	 * platform they were written.
	 *
	 * We map the DLT_* codes on this platform, whatever
	 * it might be, to the corresponding LINKTYPE_* codes.
	 */
	if (dlt == DLT_ATM_RFC1483)
		return (LINKTYPE_ATM_RFC1483);
	if (dlt == DLT_RAW)
		return (LINKTYPE_RAW);
	if (dlt == DLT_SLIP_BSDOS)
		return (LINKTYPE_SLIP_BSDOS);
	if (dlt == DLT_PPP_BSDOS)
		return (LINKTYPE_PPP_BSDOS);

	/*
	 * These DLT_* codes were originally defined on some platform,
	 * and weren't defined on other platforms.
	 *
	 * At least some of them have values, on at least one platform,
	 * that collide with other DLT_* codes on other platforms, e.g.
	 * DLT_LOOP, so we don't just define them, on all platforms,
	 * as having the same value as on the original platform.
	 *
	 * Therefore, we assigned new LINKTYPE_* codes to them, and,
	 * on the platforms where they weren't originally defined,
	 * define the DLT_* codes to have the same value as the
	 * corresponding LINKTYPE_* codes.
	 *
	 * This means that, for capture files with the original
	 * platform's DLT_* code rather than the LINKTYPE_* code
	 * as a link-layer type, we will recognize those types
	 * on that platform, but not on other platforms.
	 */
#ifdef DLT_FR
	/* BSD/OS Frame Relay */
	if (dlt == DLT_FR)
		return (LINKTYPE_FRELAY);
#endif
#if DLT_HDLC != LINKTYPE_NETBSD_HDLC
	/* NetBSD HDLC */
	if (dlt == DLT_HDLC)
		return (LINKTYPE_NETBSD_HDLC);
#endif
#if DLT_C_HDLC != LINKTYPE_C_HDLC
	/* BSD/OS Cisco HDLC */
	if (dlt == DLT_C_HDLC)
		return (LINKTYPE_C_HDLC);
#endif
#if DLT_LOOP != LINKTYPE_LOOP
	/* OpenBSD DLT_LOOP */
	if (dlt == DLT_LOOP)
		return (LINKTYPE_LOOP);
#endif
#if DLT_ENC != LINKTYPE_ENC
	/* OpenBSD DLT_ENC */
	if (dlt == DLT_ENC)
		return (LINKTYPE_ENC);
#endif

	/*
	 * These DLT_* codes are not on all platforms, but, so far,
	 * there don't appear to be any platforms that define
	 * other codes with those values; we map them to
	 * different LINKTYPE_* codes anyway, just in case.
	 */
	/* Linux ATM Classical IP */
	if (dlt == DLT_ATM_CLIP)
		return (LINKTYPE_ATM_CLIP);

	/*
	 * A few other values, defined on some platforms, not in
	 * either matching range, but not colliding with anything
	 * else, so they're given the same LINKTYPE_* code as
	 * their DLT_* code.
	 */
	if (dlt == DLT_REDBACK_SMARTEDGE || dlt == DLT_PPP_SERIAL ||
	    dlt == DLT_PPP_ETHER || dlt == DLT_SYMANTEC_FIREWALL)
		return (dlt);

	/*
	 * If we don't have a mapping for this DLT_* code, return an
	 * error; that means that this is a DLT_* value with no
	 * corresponding LINKTYPE_ value, and we need to assign one.
	 */
	return (-1);
}

/*
 * Map a LINKTYPE_* code to the corresponding DLT_* code.
 * Used to translate link-layer types in savefiles to the
 * DLT_* codes to provide to callers of libpcap.
 */
int
linktype_to_dlt(int linktype)
{
	/*
	 * All values in the low matching range were handed out before
	 * assigning DLT_* codes became a free-for-all, so they're the
	 * same on all platforms, and are thus used as the LINKTYPE_*
	 * codes in capture files.
	 */
	if (linktype >= LINKTYPE_LOW_MATCHING_MIN &&
	    linktype <= LINKTYPE_LOW_MATCHING_MAX)
		return (linktype);

#if LINKTYPE_PFSYNC != DLT_PFSYNC
	/*
	 * DLT_PFSYNC has a code on several platforms that's in the
	 * non-matching range, a code on FreeBSD that's in the high
	 * matching range and that's *not* equal to LINKTYPE_PFSYNC,
	 * and has a code on the rmaining platforms that's equal
	 * to LINKTYPE_PFSYNC, which is in the high matching range.
	 *
	 * Map LINKTYPE_PFSYNC to whatever DLT_PFSYNC is on this
	 * platform, if the two aren't equal.
	 */
	if (linktype == LINKTYPE_PFSYNC)
		return (DLT_PFSYNC);
#endif

	/*
	 * DLT_PKTAP is defined as DLT_USER2 - which is in the high
	 * matching range - on Darwin because Apple used DLT_USER2
	 * on systems that users ran, not just as an internal thing.
	 *
	 * We map LINKTYPE_PKTAP to the platform's DLT_PKTAP for
	 * the benefit of software that's expecting DLT_PKTAP
	 * (even if that's DLT_USER2) for an Apple PKTAP capture.
	 *
	 * (Yes, this is an annoyance if you want to read a
	 * LINKTYPE_USER2 packet as something other than DLT_PKTAP
	 * on a Darwin-based OS, as, on that OS, DLT_PKTAP and DLT_USER2
	 * are the same.  Feel free to complain to Apple about this.)
	 */
#if LINKTYPE_PKTAP != DLT_PKTAP
	if (linktype == LINKTYPE_PKTAP)
		return (DLT_PKTAP);
#endif

	/*
	 * These DLT_* codes have different values on different
	 * platforms, so we assigned them LINKTYPE_* codes just
	 * below the lower bound of the high matchig range;
	 * those values should never be equal to any DLT_*
	 * code, so that should avoid collisions.
	 *
	 * That way, for example, "raw IP" packets will have
	 * LINKTYPE_RAW as the code in all savefiles for
	 * which the code that writes them maps to that
	 * value, regardless of the platform on which they
	 * were written, so they should be readable on all
	 * platforms without having to determine on which
	 * platform they were written.
	 *
	 * We map the LINKTYPE_* codes to the corresponding
	 * DLT_* code on this platform.
	 */
	if (linktype == LINKTYPE_ATM_RFC1483)
		return (DLT_ATM_RFC1483);
	if (linktype == LINKTYPE_RAW)
		return (DLT_RAW);
	if (linktype == LINKTYPE_SLIP_BSDOS)
		return (DLT_SLIP_BSDOS);
	if (linktype == LINKTYPE_PPP_BSDOS)
		return (DLT_PPP_BSDOS);

	/*
	 * These DLT_* codes were originally defined on some platform,
	 * and weren't defined on other platforms.
	 *
	 * At least some of them have values, on at least one platform,
	 * that collide with other DLT_* codes on other platforms, e.g.
	 * DLT_LOOP, so we don't just define them, on all platforms,
	 * as having the same value as on the original platform.
	 *
	 * Therefore, we assigned new LINKTYPE_* codes to them, and,
	 * on the platforms where they weren't originally defined,
	 * define the DLT_* codes to have the same value as the
	 * corresponding LINKTYPE_* codes.
	 *
	 * This means that, for capture files with the original
	 * platform's DLT_* code rather than the LINKTYPE_* code
	 * as a link-layer type, we will recognize those types
	 * on that platform, but not on other platforms.
	 *
	 * We map the LINKTYPE_* codes to the corresponding
	 * DLT_* code on platforms where the two codes differ..
	 */
#ifdef DLT_FR
	/* BSD/OS Frame Relay */
	if (linktype == LINKTYPE_FRELAY)
		return (DLT_FR);
#endif
#if LINKTYPE_NETBSD_HDLC != DLT_HDLC
	/* NetBSD HDLC */
	if (linktype == LINKTYPE_NETBSD_HDLC)
		return (DLT_HDLC);
#endif
#if LINKTYPE_C_HDLC != DLT_C_HDLC
	/* BSD/OS Cisco HDLC */
	if (linktype == LINKTYPE_C_HDLC)
		return (DLT_C_HDLC);
#endif
#if LINKTYPE_LOOP != DLT_LOOP
	/* OpenBSD DLT_LOOP */
	if (linktype == LINKTYPE_LOOP)
		return (DLT_LOOP);
#endif
#if LINKTYPE_ENC != DLT_ENC
	/* OpenBSD DLT_ENC */
	if (linktype == LINKTYPE_ENC)
		return (DLT_ENC);
#endif

	/*
	 * These DLT_* codes are not on all platforms, but, so far,
	 * there don't appear to be any platforms that define
	 * other codes with those values; we map them to
	 * different LINKTYPE_* values anyway, just in case.
	 *
	 * LINKTYPE_ATM_CLIP is a special case.  DLT_ATM_CLIP is
	 * not on all platforms, but, so far, there don't appear
	 * to be any platforms that define it as anything other
	 * than 19; we define LINKTYPE_ATM_CLIP as something
	 * other than 19, just in case.  That value is in the
	 * high matching range, so we have to check for it.
	 */
	/* Linux ATM Classical IP */
	if (linktype == LINKTYPE_ATM_CLIP)
		return (DLT_ATM_CLIP);

	/*
	 * For all other values, return the linktype code as the
	 * DLT_* code.
	 *
	 * If the code is in the high matching range, the
	 * DLT_* code is the same as the LINKTYPE_* code.
	 *
	 * If the code is greater than the maximum value in
	 * the high matching range, it may be a value from
	 * a newer version of libpcap; we provide it in case
	 * the program' capable of handling it.
	 *
	 * If the code is less than the minimum value in the
	 * high matching range, it might be from a capture
	 * written by code that doesn't map non-matching range
	 * DLT_* codes to the appropriate LINKTYPE_* code, so
	 * we'll just pass it through, so that *if it was written
	 * on this platform* it will be interpreted correctly.
	 * (We don't know whether it was written on this platform,
	 * but at least this way there's *some* chance that it
	 * can be read.)
	 */
	return linktype;
}

/*
 * Return the maximum snapshot length for a given DLT_ value.
 *
 * For most link-layer types, we use MAXIMUM_SNAPLEN.
 *
 * For DLT_DBUS, the maximum is 128MiB, as per
 *
 *    https://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-messages
 *
 * For DLT_EBHSCR, the maximum is 8MiB, as per
 *
 *    https://www.elektrobit.com/ebhscr
 *
 * For DLT_USBPCAP, the maximum is 1MiB, as per
 *
 *    https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=15985
 */
u_int
max_snaplen_for_dlt(int dlt)
{
	switch (dlt) {

	case DLT_DBUS:
		return 128*1024*1024;

	case DLT_EBHSCR:
		return 8*1024*1024;

	case DLT_USBPCAP:
		return 1024*1024;

	default:
		return MAXIMUM_SNAPLEN;
	}
}