tcprewrite(1)

NAME
*[B-Font]tcprewrite - Rewrite the packets in a pcap file.

SYNOPSIS
*[B-Font]tcprewrite [*[B-Font]-flags] [*[B-Font]-flag [*[I-Font]value]] [*[B-Font]--option-name[[=| ]*[I-Font]value]]

All arguments must be options.

DESCRIPTION
Tcprewrite is a tool to rewrite packets stored in pcap(3) file format, such as created by tools such as tcpdump(1) and wireshark(1). Once a pcap file has had it's packets rewritten, they can be replayed back out on the network using tcpreplay(1).

tcprewrite currently supports reading the following DLT types:

DLT_C_HDLC aka Cisco HDLC

DLT_EN10MB aka Ethernet

DLT_LINUX_SLL aka Linux Cooked Socket

DLT_LINUX_SLL2 aka Linux Cooked Socket v2

DLT_RAW aka RAW IP

DLT_NULL aka BSD Loopback

DLT_LOOP aka OpenBSD Loopback

DLT_IEEE802_11 aka 802.11a/b/g

DLT_IEEE802_11_RADIO aka 802.11a/b/g with Radiotap headers

DLT_JUNIPER_ETHER aka Juniper Encapsulated Ethernet

DLT_PPP_SERIAL aka PPP over Serial

Please see the --dlt option for supported DLT types for writing.

The packet editing features of tcprewrite which distinguish between "client" and "server" traffic requires a tcpprep(1) cache file.

For more details, please see the Tcpreplay Manual at: http://tcpreplay.appneta.com

OPTIONS

Rewrite TCP/UDP ports.
    This option may appear up to 9999 times.

    Specify a list of comma delimited port mappings consisting of colon delimited port number pairs. Each colon delimited port pair consists of the port to match followed by the port number to rewrite.

    Examples:
        --portmap=80:8000 --portmap=8080:80    # 80->8000 and 8080->80
        --portmap=8000,8080,88888:80           # 3 different ports become 80
        --portmap=8000-8999:80                 # ports 8000 to 8999 become 80

Randomize src/dst IPv4/v6 addresses w/ given seed.
    This option may appear up to 1 times. This option must not appear in combination with any of the following options: fuzz-seed. This option takes an integer number as its argument.

    Causes the source and destination IPv4/v6 addresses to be pseudo randomized but still maintain client/server relationships. Since the randomization is deterministic based on the seed, you can reuse the same seed value to recreate the traffic.

Rewrite IPv4/v6 addresses using pseudo-NAT.
    This option may appear up to 2 times. This option must not appear in combination with any of the following options: srcipmap.

    Takes a comma delimited series of colon delimited CIDR netblock pairs. Each netblock pair is evaluated in order against the IP addresses. If the IP address in the packet matches the first netblock, it is rewritten using the second netblock as a mask against the high order bits.

    IPv4 Example:
        --pnat=192.168.0.0/16:10.77.0.0/16,172.16.0.0/12:10.1.0.0/24
    IPv6 Example:
        --pnat=[2001:db8::/32]:[dead::/16],[2001:db8::/32]:[::ffff:0:0/96]

Rewrite source IPv4/v6 addresses using pseudo-NAT.
    This option may appear up to 1 times. This option must not appear in combination with any of the following options: pnat.

    Works just like the --pnat option, but only affects the source IP addresses in the IPv4/v6 header.

Rewrite destination IPv4/v6 addresses using pseudo-NAT.
    This option may appear up to 1 times. This option must not appear in combination with any of the following options: pnat.

    Works just like the --pnat option, but only affects the destination IP addresses in the IPv4/v6 header.

Rewrite IP addresses to be between two endpoints.
    This option may appear up to 1 times. This option must appear in combination with the following options: cachefile.

    Takes a pair of colon delimited IPv4/v6 addresses which will be used to rewrite all traffic to appear to be between the two IP addresses.

    IPv4 Example:
        --endpoints=172.16.0.1:172.16.0.2
    IPv6 Example:
        --endpoints=[2001:db8::dead:beef]:[::ffff:0:0:ac:f:0:2]

Change TCP Sequence (and ACK) numbers /w given seed.
    This option takes an integer number as its argument. The value of *[I-Font]number is constrained to being:
    greater than or equal to 1
    The default *[I-Font]number for this option is:
     0

    Change all TCP sequence numbers, and related sequence-acknowledgement numbers. They will be shifted by a random amount based on the provided seed.

Skip rewriting broadcast/multicast IPv4/v6 addresses.

    By default --seed, --pnat and --endpoints will rewrite
    broadcast and multicast IPv4/v6 and MAC addresses.    Setting this flag
    will keep broadcast/multicast IPv4/v6 and MAC addresses from being rewritten.

Force recalculation of IPv4/TCP/UDP header checksums.

    Causes each IPv4/v6 packet to have their checksums recalculated and fixed. Automatically enabled for packets modified with --seed, --pnat, --endpoints or --fixlen.

Alter IP/TCP header len to match packet length.

    By default, tcpreplay will send packets with the original packet length, However, you may want the packet length revised to minimum packet size. Using this option, tcpreplay will rewrite (fix) the packet length, and recalculate checksums when packet length changes. Caution: undesired packet changes may occur when this option is specified.

Override default MTU length (1500 bytes).
    This option may appear up to 1 times. This option takes an integer number as its argument. The value of *[I-Font]number is constrained to being:
    in the range  1 through MAX_SNAPLEN

    Override the default 1500 byte MTU size for determining the maximum padding length (--fixlen=pad) or when truncating (--mtu-trunc).

Truncate packets larger then specified MTU.
    This option may appear up to 1 times.

    Similar to --fixlen, this option will truncate data in packets from Layer 3 and above to be no larger then the MTU.

Remove Ethernet checksums (FCS) from end of frames.

    Note, this option is pretty dangerous! We do not actually check to see if a FCS actually exists in the frame, we just blindly delete the last 4 bytes. Hence, you should only use this if you know know that your OS provides the FCS when reading raw packets.

Modify the IPv4/v6 TTL/Hop Limit.

    Allows you to modify the TTL/Hop Limit of all the IPv4/v6 packets. Specify a number to hard-code the value or +/-value to increase or decrease by the value provided (limited to 1-255).

    Examples:
        --ttl=10
        --ttl=+7
        --ttl=-64

Set the IPv4 TOS/DiffServ/ECN byte.
    This option may appear up to 1 times. This option takes an integer number as its argument. The value of *[I-Font]number is constrained to being:
    in the range  0 through 255

    Allows you to override the TOS (also known as DiffServ/ECN) value in IPv4.

Set the IPv6 Traffic Class byte.
    This option may appear up to 1 times. This option takes an integer number as its argument. The value of *[I-Font]number is constrained to being:
    in the range  0 through 255

    Allows you to override the IPv6 Traffic Class field.

Set the IPv6 Flow Label.
    This option may appear up to 1 times. This option takes an integer number as its argument. The value of *[I-Font]number is constrained to being:
    in the range  0 through 1048575

    Allows you to override the 20bit IPv6 Flow Label field. Has no effect on IPv4 packets.

Pad or truncate packet data to match header length.
    This option may appear up to 1 times.

    Packets may be truncated during capture if the snaplen is smaller then the packet. This option allows you to modify the packet to pad the packet back out to the size stored in the IPv4/v6 header or rewrite the IP header total length to reflect the stored packet length.

    pad Truncated packets will be padded out so that the packet length matches the IPv4 total length

    trunc Truncated packets will have their IPv4 total length field rewritten to match the actual packet length

    del Delete the packet

Fuzz 1 in X packets. Edit bytes, length, or emulate packet drop.
    This option takes an integer number as its argument. The value of *[I-Font]number is constrained to being:
    greater than or equal to 0
    The default *[I-Font]number for this option is:
     0

    This fuzzing was designed as to test layer 7 protocols such as voip protocols. It modifies randomly 1 out of X packets (where X = --fuzz-factor) in order for stateful protocols to cover more of their code. The random fuzzing actions focus on data start and end because it often is the part of the data application protocols base their decisions on.

    Possible fuzzing actions list:
     * drop packet
     * reduce packet size
     * edit packet Bytes:
       * Not all Bytes have the same probability of appearance in real life.
         Replace with 0x00, 0xFF, or a random byte with equal likelihood.
       * Not all Bytes have the same significance in a packet.
         Replace the start, the end, or the middle of the packet with equal likelihood.
     * do nothing (7 out of 8 packets)

Set the Fuzz 1 in X packet ratio (default 1 in 8 packets).
    This option must appear in combination with the following options: fuzz-seed. This option takes an integer number as its argument. The value of *[I-Font]number is constrained to being:
    greater than or equal to 1
    The default *[I-Font]number for this option is:
     8

    Sets the ratio of for --fuzz-seed option. By default this value is 8, which means 1 in 8 packets are modified by fuzzing. Note that this ratio is based on the random number generated by the supplied fuzz seed. Therefore by default you cannot expect that exactly every eighth packet will be modified.

Skip rewriting broadcast/multicast Layer 2 addresses.

    By default, editing Layer 2 addresses will rewrite
    broadcast and multicast MAC addresses.    Setting this flag
    will keep broadcast/multicast MAC addresses from being rewritten.

Override output DLT encapsulation.
    This option may appear up to 1 times.

    By default, no DLT (data link type) conversion will be made. To change the DLT type of the output pcap, select one of the following values:

    enet Ethernet aka DLT_EN10MB

    hdlc Cisco HDLC aka DLT_C_HDLC

    jnpr_eth Juniper Ethernet DLT_C_JNPR_ETHER

    pppserial PPP Serial aka DLT_PPP_SERIAL

    user User specified Layer 2 header and DLT type

Override destination ethernet MAC addresses.
    This option may appear up to 1 times.

    Takes a pair of comma deliminated ethernet MAC addresses which will replace the destination MAC address of outbound packets. The first MAC address will be used for the server to client traffic and the optional second MAC address will be used for the client to server traffic.

    Example:
        --enet-dmac=00:12:13:14:15:16,00:22:33:44:55:66

Override source ethernet MAC addresses.
    This option may appear up to 1 times.

    Takes a pair of comma deliminated ethernet MAC addresses which will replace the source MAC address of outbound packets. The first MAC address will be used for the server to client traffic and the optional second MAC address will be used for the client to server traffic.

    Example:
        --enet-smac=00:12:13:14:15:16,00:22:33:44:55:66

Substitute MAC addresses.
    This option may appear up to 9999 times.

    Allows you to rewrite ethernet MAC addresses of packets. It takes comma delimited pair or MACs address and rewrites all occurrences of the first MAC with the value of the second MAC. Example:
        --enet-subsmac=00:12:13:14:15:16,00:22:33:44:55:66

Randomize MAC addresses.
    This option may appear up to 1 times. This option must not appear in combination with any of the following options: enet-smac, enet-dmac, enet-subsmac. This option takes an integer number as its argument.

    Allows you to randomize ethernet MAC addresses of packets, mostly like what --seed option does for IPv4/IPv6 addresses.

Randomize MAC addresses.
    This option may appear up to 1 times. This option must appear in combination with the following options: enet-mac-seed. This option takes an integer number as its argument. The value of *[I-Font]number is constrained to being:
    in the range  1 through 6

    Keep some bytes untouched when usinging --enet-mac-seed option.

Specify ethernet 802.1q VLAN tag mode.
    This option may appear up to 1 times.

    Allows you to rewrite ethernet frames to add a 802.1q header to standard 802.3 ethernet headers or remove the 802.1q VLAN tag information.

    add Adds an 802.1q VLAN header to the existing 802.3 ethernet header. If a VLAN header already exists, a new VLAN header is added outside of the existing header.

    Note that you will be allowed to run this option multiple times to create more than 2 VLAN headers, however those packets will be valid. At most you should have 2 X 802.1q VLAN tags, or outer an 802.1ad and an inner 802.1q VLAN tag.

    del Rewrites the existing 802.1q VLAN header as an 802.3 ethernet header

Specify the new ethernet 802.1q VLAN tag value.
    This option may appear up to 1 times. This option must appear in combination with the following options: enet-vlan. This option takes an integer number as its argument. The value of *[I-Font]number is constrained to being:
    in the range  0 through 4095

    Mandatory when --enet-vlan=add is used on packets that are not already VLAN tagged.

Specify the ethernet 802.1q VLAN CFI value.
    This option may appear up to 1 times. This option must appear in combination with the following options: enet-vlan. This option takes an integer number as its argument. The value of *[I-Font]number is constrained to being:
    in the range  0 through 1

    When omitted, the CFI bit of an existing VLAN header is preserved; a newly added tag on a previously untagged packet defaults to 0 (a one-time notice is printed).

Specify the ethernet 802.1q VLAN priority.
    This option may appear up to 1 times. This option must appear in combination with the following options: enet-vlan. This option takes an integer number as its argument. The value of *[I-Font]number is constrained to being:
    in the range  0 through 7

    When omitted, the priority of an existing VLAN header is preserved; a newly added tag on a previously untagged packet defaults to 0 (a one-time notice is printed).

Specify VLAN tag protocol 802.1q or 802.1ad.
    This option may appear up to 1 times.

    Allows you to specify the protocol of the added VLAN tags.

    802.1q Specifies that 802.1q VLAN headers are to be added. This is the default.

    802.1ad Specifies that 802.1ad Q-in-Q VLAN headers are to be added. To make valid packets, input packets must already have 802.1q VLAN headers.

Specify HDLC control value.
    This option may appear up to 1 times. This option takes an integer number as its argument.

    The Cisco HDLC header has a 1 byte "control" field. Apparently this should always be 0, but if you can use any 1 byte value.

Specify HDLC address.
    This option may appear up to 1 times. This option takes an integer number as its argument.

    The Cisco HDLC header has a 1 byte "address" field which has two valid values:

    0x0F Unicast

    0xBF Broadcast
    You can however specify any single byte value.

Set output file DLT type.
    This option may appear up to 1 times. This option takes an integer number as its argument.

    Set the DLT value of the output pcap file.

Rewrite Data-Link layer with user specified data.
    This option may appear up to 2 times.

    Provide a series of comma deliminated hex values which will be used to rewrite or create the Layer 2 header of the packets. The first instance of this argument will rewrite both server and client traffic, but if this argument is specified a second time, it will be used for the client traffic.

    Example:
        --user-dlink=01,02,03,04,05,06,00,1A,2B,3C,4D,5E,6F,08,00

Enable debugging output.
    This option may appear up to 1 times. This option takes an integer number as its argument. The value of *[I-Font]number is constrained to being:
    in the range  0 through 5
    The default *[I-Font]number for this option is:
     0

    If configured with --enable-debug, then you can specify a verbosity level for debugging output. Higher numbers increase verbosity.

Input pcap file to be processed.
    This option may appear up to 1 times.

Output pcap file.
    This option may appear up to 1 times.

Split traffic via tcpprep cache file.
    This option may appear up to 1 times.

    Use tcpprep cache file to split traffic based upon client/server relationships.

Print decoded packets via tcpdump to STDOUT.
    This option may appear up to 1 times.

Arguments passed to tcpdump decoder.
    This option may appear up to 1 times. This option must appear in combination with the following options: verbose.

    When enabling verbose mode (-v) you may also specify one or more additional arguments to pass to tcpdump to modify the way packets are decoded. By default, -n and -l are used. Be sure to quote the arguments so that they are not interpreted by tcprewrite. Please see the tcpdump(1) man page for a complete list of options.

Parse fragroute configuration file.
    This option may appear up to 1 times.

    Enable advanced evasion techniques using the built-in fragroute(8) engine. See the fragroute(8) man page for more details. Important: tcprewrite does not support the delay, echo or print commands.

Which flows to apply fragroute to: c2s, s2c, both.
    This option may appear up to 1 times. This option must appear in combination with the following options: cachefile.

    Apply the fragroute engine to packets going c2s, s2c or both when using a cache file.

Skip writing packets with soft errors.
    This option may appear up to 1 times.

    In some cases, packets can not be decoded or the requested editing is not possible. Normally these packets are written to the output file unedited so that tcpprep cache files can still be used, but if you wish, these packets can be suppressed.

    One example of this is 802.11 management frames which contain no data.

Print version information.

Display less usage information and exit.

suppress printing warning messages.

Display usage information and exit.

Pass the extended usage information through a pager.

Save the option state to cfgfile.  The default is the last
    configuration file listed in the OPTION PRESETS section, below. The command will exit after updating the config file.

Load options from cfgfile.
    The no-load-opts form will disable the loading of earlier config/rc/ini files. --no-load-opts is handled early, out of order.

OPTION PRESETS
Any option that is not marked as not presettable may be preset by loading values from configuration ("RC" or ".INI") file(s). The homerc file is "$$/", unless that is a directory. In that case, the file ".tcprewriterc" is searched for within that directory.

FILES
See OPTION PRESETS for configuration files.

EXIT STATUS
One of the following exit values will be returned:

Successful program execution.

The operation failed or the command syntax was not valid.

A specified configuration file could not be loaded.

libopts had an internal operational error.  Please report
    it to autogen-users@lists.sourceforge.net. Thank you.

AUTHORS
Copyright 2013-2026 Fred Klassen - AppNeta Copyright 2000-2012 Aaron Turner For support please use the tcpreplay-users@lists.sourceforge.net mailing list. The latest version of this software is always available from: http://tcpreplay.appneta.com/

COPYRIGHT
Copyright (C) 2000-2026 Aaron Turner and Fred Klassen all rights reserved. This program is released under the terms of the GNU General Public License, version 3 or later.

BUGS
Please send bug reports to: tcpreplay-users@lists.sourceforge.net

NOTES
This manual page was AutoGen-erated from the tcprewrite option definitions.