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PROGRAM:
NAME
bittwiste -- pcap capture file editor
SYNOPSIS
bittwiste [ -I input ] [ -O output ] [ -L layer ] [ -X payload ]
[ -C ] [ -M linktype ] [ -D offset ] [ -R range ]
[ -S timeframe ] [ -T header ]
[ header-specific-options ] [ -h ]
DESCRIPTION
This document describes the bittwiste program, the pcap(3) capture file editor. Bittwiste
is designed to work only with Ethernet frame, e.g. link type DLT_EN10MB in pcap(3), with a
maximum frame size of 1514 bytes which is equivalent to a MTU of 1500 bytes, 14 bytes for
Ethernet header.
Bittwiste can currently edit Ethernet, ARP, IP, ICMP, TCP, and UDP headers. If run with
the -X flag, you can append your own payload after any of these headers; specified using
the -L and -T flag. Bittwiste will, if not run with the -C flag, recalculate the checksums
for IP, ICMP, TCP, and UDP packets, except for the last fragment of a fragmented IP
datagram; bittwiste does not currently support checksum correction for the last fragment
of a fragmented IP datagram. While parsing the packets in a trace file, bittwiste will
skip, i.e. write to output file as is, any truncated packet, for example, an ICMP packet
with a captured length of 25 bytes (we need at least 28 bytes; 14 bytes for Ethernet
header, minimum 20 bytes for IP header, and 4 bytes for ICMP header) does not give enough
information on its ICMP header for bittwiste to read and modify it. In this case, you can
utilize the -L and -T flag to copy the original packet up to its IP header and append your
customized ICMP header and data to the packet using the -X flag. When specifying payload
that covers the ICMP, TCP or UDP header and its data, you can use zeros, e.g. 0000 for 2
bytes of zeros, for the header checksum which is then corrected automatically by
bittwiste.
In order to simplify the way options are specified, you can only edit packets of a
specific type supplied to the -T flag per execution of bittwiste on a trace file. In
addition, the -T flag must appear last among the general options which are the -I, -O, -L,
-X, -C, -M, -D, -R and -S flag.
OPTIONS
-I input
Input pcap based trace file.
-O output
Output trace file.
-L layer
Copy up to the specified layer and discard the remaining data. Value for layer must
be either 2, 3 or 4 where 2 for Ethernet, 3 for ARP or IP, and 4 for ICMP, TCP or
UDP.
-X payload
Append payload in hex digits to the end of each packet.
Example: -X 0302aad1
-X flag is ignored if -L and -T flag are not specified.
-C Specify this flag to disable checksum correction. Checksum correction is applicable
for non-fragmented IP, ICMP, TCP, and UDP packets only.
-M linktype
Replace the linktype stored in the pcap file header. Typically, value for linktype
is 1 for Ethernet.
Example: -M 12 (for raw IP), -M 51 (for PPPoE)
For the complete list, see:
http://www.tcpdump.org/linktypes.html
-D offset
Delete the specified byte offset from each packet.
First byte (starting from link layer header) starts from 1.
-L, -X, -C and -T flag are ignored if -D flag is specified.
Example: -D 15-40, -D 10 or -D 18-9999
-R range
Save only the specified range of packets.
Example: -R 5-21 or -R 9
-S timeframe
Save only the packets within the specified timeframe with up to one-second
resolution using DD/MM/YYYY,HH:MM:SS as the format for start and end time in
timeframe.
Example: -S 22/10/2006,21:47:35-24/10/2006,13:16:05
-S flag is evaluated after -R flag.
-T header
Edit only the specified header. Possible keywords for header are, eth, arp, ip,
icmp, tcp, or udp. -T flag must appear last among the general options.
-h Print version information and usage.
header-specific-options
Each packet that matches the type supplied to the -T flag is modified based on the
options described below:
Options for eth (RFC 894):
-d dmac or omac,nmac
Destination MAC address. Example: -d 00:08:55:64:65:6a
If omac and nmac are specified instead, all occurences of omac in the
destination MAC address field will be replaced with nmac.
-s smac or omac,nmac
Source MAC address. Example: -s 00:13:20:3e:ab:cf
If omac and nmac are specified instead, all occurences of omac in the source
MAC address field will be replaced with nmac.
-t type
EtherType. Possible keywords for type are, ip and arp only.
Options for arp (RFC 826):
-o opcode
Operation code in integer value between 0 to 65535. For example, you can set
opcode to 1 for ARP request, 2 for ARP reply.
-s smac or omac,nmac
Sender MAC address. Example: -s 00:13:20:3e:ab:cf
If omac and nmac are specified instead, all occurences of omac in the sender
MAC address field will be replaced with nmac.
-p sip or oip,nip
Sender IP address. Example: -p 192.168.0.1
If oip and nip are specified instead, all occurences of oip in the sender IP
address field will be replaced with nip.
-t tmac or omac,nmac
Target MAC address. Example: -t 00:08:55:64:65:6a
If omac and nmac are specified instead, all occurences of omac in the target
MAC address field will be replaced with nmac.
-q tip or oip,nip
Target IP address. Example: -q 192.168.0.2
If oip and nip are specified instead, all occurences of oip in the target IP
address field will be replaced with nip.
Options for ip (RFC 791):
-i id
Identification in integer value between 0 to 65535.
-f flags
Control flags. Possible characters for flags are:
- : remove all flags
r : set the reserved flag
d : set the don't fragment flag
m : set the more fragment flag
Example: -f d
If any of the flags is specified, all original flags are removed
automatically.
-o offset
Fragment offset in integer value between 0 to 7770. Value for offset
represents the number of 64-bit segments contained in earlier fragments
which must not exceed 7770 (62160 bytes).
-t ttl
Time to live in integer value between 0 to 255 (milliseconds).
-p proto
Protocol number in integer value between 0 to 255. Some common protocol
numbers are:
1 : Internet Control Message Protocol (ICMP)
6 : Transmission Control Protocol (TCP)
17 : User Datagram Protocol (UDP)
For the complete list, see:
http://www.iana.org/assignments/protocol-numbers
-s sip or oip,nip
Source IP address. Example: -s 192.168.0.1
If oip and nip are specified instead, all occurences of oip in the source IP
address field will be replaced with nip.
-d dip or oip,nip
Destination IP address. Example: -d 192.168.0.2
If oip and nip are specified instead, all occurences of oip in the
destination IP address field will be replaced with nip.
Options for icmp (RFC 792):
-t type
Type of message in integer value between 0 to 255. Some common messages are:
0 : Echo reply
3 : Destination unreachable
8 : Echo
11 : Time exceeded
For the complete list, see:
http://www.iana.org/assignments/icmp-parameters
-c code
Error code for this ICMP message in integer value between 0 to 255. For
example, code for time exceeded message may have one of the following
values:
0 : transit TTL exceeded
1 : reassembly TTL exceeded
For the complete list, see:
http://www.iana.org/assignments/icmp-parameters
Options for tcp (RFC 793):
-s sport or op,np
Source port number in integer value between 0 to 65535. If op and np are
specified instead, all occurrences of op in the source port field will be
replaced with np.
-d dport or op,np
Destination port number in integer value between 0 to 65535. If op and np
are specified instead, all occurrences of op in the destination port field
will be replaced with np.
-q seq
Sequence number in integer value between 0 to 4294967295. If SYN control bit
is set, e.g. character s is supplied to the -f flag, seq represents the
initial sequence number (ISN) and the first data byte is ISN + 1.
-a ack
Acknowledgment number in integer value between 0 to 4294967295. If ACK
control bit is set, e.g. character a is supplied to the -f flag, ack
represents the value of the next sequence number that the receiver is
expecting to receive.
-f flags
Control flags. Possible characters for flags are:
- : remove all flags
u : urgent pointer field is significant
a : acknowledgment field is significant
p : push function
r : resets the connection
s : synchronizes the sequence numbers
f : no more data from sender
Example: -f s
If any of the flags is specified, all original flags are removed
automatically.
-w win
Window size in integer value between 0 to 65535. If ACK control bit is set,
e.g. character a is supplied to the -f flag, win represents the number of
data bytes, beginning with the one indicated in the acknowledgment number
field that the receiver is willing to accept.
-u urg
Urgent pointer in integer value between 0 to 65535. If URG control bit is
set, e.g. character u is supplied to the -f flag, urg represents a pointer
that points to the first data byte following the urgent data.
Options for udp (RFC 768):
-s sport or op,np
Source port number in integer value between 0 to 65535. If op and np are
specified instead, all occurrences of op in the source port field will be
replaced with np.
-d dport or op,np
Destination port number in integer value between 0 to 65535. If op and np
are specified instead, all occurrences of op in the destination port field
will be replaced with np.
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