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domain
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Specifies the domain where traffic is captured:
-
0—br1, captures traffic from the management interface
-
1—Router, captures traffic from the configured data interfaces
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-A
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Prints each packet (minus its link level header) in ASCII. Handy
for capturing web pages.
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-B
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Sets the operating system capture buffer size to buffer_size.
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-c
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Exits after receiving count packets.
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-C
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Before writing a raw packet to a savefile, checks whether the
file is currently larger than file_size and, if so, close the current savefile
and open a new one. Savefiles after the first savefile will have the name
specified with the -w flag, with a number after it, starting at 1 and
continuing upward. The units of file_size are millions of bytes (1,000,000
bytes, not 1,048,576 bytes).
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-d
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Dumps the compiled packet-matching code in a human readable form
to standard output and stop.
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-dd
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Dumps packet-matching code as a C program fragment.
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-ddd
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Dumps packet-matching code as decimal numbers (preceded with a
count).
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-D
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Prints the list of the network interfaces available on the
system and on which tcpdump can capture packets. For each network interface, a
number and an interface name, possibly followed by a text description of the
interface, is printed. The interface name or the number can be supplied to the
-i flag to specify an interface on which to capture.
This can be useful on systems that do not have a command to list
them (Windows systems, or UNIX systems lacking ifconfig -a); the number can be
useful on Windows 2000 and later systems, where the interface name is a
somewhat complex string.
The -D flag will not be supported if tcpdump was built with an
older version of libpcap that lacks the pcap_findaclldevs() function.
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-e
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Prints the link-level header on each dump line.
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-E
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Uses spi@ipaddr algo:secret for decrypting IPsec ESP packets
that are addressed to addr and contain Security Parameter Index value spi. This
combination may be repeated with comma or newline separation.
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-f
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Prints ‘foreign’ IPv4 addresses numerically rather than
symbolically (this option is intended to get around serious brain damage in
Sun's NIS server usually it hangs forever translating non-local internet
numbers).
The test for ‘foreign’ IPv4 addresses is done using the IPv4
address and netmask of the interface on which capture is being done.
If that address or netmask are not available, available, either
because the interface on which capture is being done has no address or netmask
or because the capture is being done on the Linux 'any' interface, which can
capture on more than one interface, this option will not work correctly.
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-F
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Uses file as input for the filter expression. An additional
expression given on the command line is ignored.
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-G
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If specified, rotates the dump file specified with the -w option
every rotate_seconds seconds.
Savefiles will have the name specified by -w which should
include a time format as defined by strftime(3). If no time format is
specified, each new file will overwrite the previous.
If used in conjunction with the -C option, filenames will take
the form of ‘file<count>’.
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-I
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Puts the interface in ‘monitor mode’; this is supported only on
IEEE 802.11 Wi-Fi interfaces, and supported only on some operating systems.
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-K
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Does not attempt to verify TCP checksums.
This is useful for interfaces that perform the TCP checksum
calculation in hardware; otherwise, all outgoing TCP checksums will be flagged
as bad.
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-l
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Makes stdout line buffered. Useful if you want to see the data
while capturing it. Example, ‘‘tcpdump -l | tee dat” or “tcpdump -l > dat
& tail -f dat”.
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-L
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Lists the known data link types for the interface and exit.
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-m
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Loads SMI MIB module definitions from file module.
This option can be used several times to load several MIB
modules into tcpdump.
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-M
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Uses secret as a shared secret for validating the digests found
in TCP segments with the TCP-MD5 option (RFC 2385), if present.
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-n
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Does not convert addresses (i.e., host addresses, port numbers,
etc.) to names.
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-N
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Does not print domain name qualification of host names.
Example, if you give this flag then tcpdump will print “nic”
instead of “nic.ddn.mil”.
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-O
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Does not run the packet-matching code optimizer. This is useful
only if you suspect a bug in the optimizer.
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-p
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Does not put the interface into promiscuous mode. Note that the
interface might be in promiscuous mode for some other reason; hence, `-p'
cannot be used as an abbreviation for `ether host {local-hw-addr} or ether
broadcast'.
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-q
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Quick output. Prints less protocol information so output lines
are shorter.
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-R
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Assumes ESP/AH packets to be based on old specification (RFC1825
to RFC1829). If specified, tcpdump will not print replay prevention field.
Because there is no protocol version field in ESP/AH
specification, tcpdump cannot deduce the version of ESP/AH protocol.
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-r
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Reads packets from file (which was created with the -w option).
Standard input is used if file is “-”.
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-S
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Prints absolute, rather than relative, TCP sequence numbers.
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-s
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Snarfs snaplen bytes of data from each packet rather than the
default of 68 (with SunOS’s NIT, the minimum is actually 96). 68 bytes is
adequate for IP, ICMP, TCP, and UDP but may truncate protocol information from
name server and NFS packets (see below). Packets truncated because of a limited
snapshot are indicated in the output with “[|proto]”, where proto is the name
of the protocol level at which the truncation has occurred.
Note that taking larger snapshots both increases the amount of
time it takes to process packets and, effectively, decreases the amount of
packet buffering. This may cause packets to be lost. You should limit snaplen
to the smallest number that will capture the protocol information you're
interested in. Setting snaplen to 0 means use the required length to catch
whole packets.
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-T
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Forces packets selected by ‘expression’ to be interpreted the
specified type. Currently known types are aodv (Ad-hoc On-demand Distance
Vector protocol), cnfp (Cisco NetFlow protocol), rpc (Remote Procedure Call),
rtp (Real-Time Applications protocol), rtcp (Real-Time Applications control
protocol), snmp (Simple Network Management Protocol), tftp (Trivial File
Transfer Protocol), vat (Visual Audio Tool), and wb (distributed White Board).
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-t
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Does not print a timestamp on each dump line.
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-tt
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Prints an unformatted timestamp on each dump line.
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-ttt
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Prints a delta (micro-second resolution) between current and
previous line on each dump line.
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-tttt
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Prints a timestamp in default format proceeded by date on each
dump line.
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-ttttt
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Prints a delta (micro-second resolution) between current and
first line on each dump line.
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-u
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Prints undecoded NFS handles.
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-U
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Makes output saved via the -w option “packet-buffered”; i.e., as
each packet is saved, it will be written to the output file, rather than being
written only when the output buffer fills.
The -U flag will not be supported if tcpdump was built with an
older version of libpcap that lacks the pcap_dump_flush() function.
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-v
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When parsing and printing, produces (slightly more) verbose
output. For example, the time to live, identification, total length and options
in an IP packet are printed. Also enables additional packet integrity checks
such as verifying the IP and ICMP header checksum.
When writing to a file with the -w option, report, every 10
seconds, the number of packets captured.
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-vv
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Even more verbose output. For example, additional fields are
printed from NFS reply packets, and SMB packets are fully decoded.
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-vvv
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Even more verbose output. For example, telnet SB... SE options
are printed in full. With -X Telnet options are printed in hex as well.
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-w
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Write the raw packets to file rather than parsing and printing
them out. They can later be printed with the -r option. Standard output is used
if file is “-”.
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-W
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Used in conjunction with the -C option, this will limit the
number of files created to the specified number, and begin over writing files
from the beginning, thus creating a ‘rotating’ buffer. In addition, it will
name the files with enough leading 0s to support the maximum number of files,
allowing them to sort correctly.
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-x
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When parsing and printing, in addition to printing the headers
of each packet, prints the data of each packet (minus its link level header) in
hex. The smaller of the entire packet or snaplen bytes will be printed. Note
that this is the entire link-layer packet, so for link layers that pad (e.g.
Ethernet), the padding bytes will also be printed when the higher layer packet
is shorter than the required padding.
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-xx
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When parsing and printing, in addition to printing the headers
of each packet, prints the data of each packet, including its link level
header, in hex.
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-X
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When parsing and printing, in addition to printing the headers
of each packet, print the data of each packet (minus its link level header) in
hex and ASCII.
This is very handy for analyzing new protocols.
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-XX
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When parsing and printing, in addition to printing the headers
of each packet, prints the data of each packet, including its link level
header, in hex and ASCII.
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-y
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Sets the data link type to use while capturing packets to
datalinktype.
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-Z
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Drops privileges (if root) and changes user ID to user and the
group ID to the primary group of user.
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