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NGREP(8)			 User Manuals			      NGREP(8)

       ngrep - network grep

       ngrep  <-hNXViwqpevxlDtTRM> <-IO	pcap_dump > < -n num > < -d dev	> < -A
       num > < -s snaplen > < -S limitlen > < -W normal|byline|single|none > <
       -c cols > < -P char > < -F file > < match expression > <	bpf filter >

       ngrep  strives  to provide most of GNU grep's common features, applying
       them to the network layer.  ngrep is a pcap-aware tool that will	 allow
       you  to specify extended	regular	expressions to match against data pay-
       loads of	packets.  It currently recognizes TCP,	UDP  and  ICMP	across
       Ethernet, PPP, SLIP, FDDI and null interfaces, and understands bpf fil-
       ter logic in the	same fashion as	more  common  packet  sniffing	tools,
       such as tcpdump(8) and snoop(1).

       -h     Display help/usage information.

       -N     Show  sub-protocol number	along with single-character identifier
	      (useful when observing raw or unknown protocols).

       -X     Treat the	match expression as a  hexadecimal  string.   See  the
	      explanation of match expression below.

       -V     Display version information.

       -i     Ignore case for the regex	expression.

       -w     Match the	regex expression as a word.

       -q     Be quiet;	don't output any information other than	packet headers
	      and their	payloads (if relevant).

       -p     Don't put	the interface into promiscuous mode.

       -e     Show  empty  packets.   Normally	empty  packets	are  discarded
	      because  they  have  no  payload to search.  If specified, empty
	      packets will be shown, regardless	of the specified regex expres-

       -v     Invert the match;	only display packets that don't	match.

       -x     Dump packet contents as hexadecimal as well as ASCII.

       -l     Make stdout line buffered.

       -D     When reading pcap_dump files, replay them	at their recorded time
	      intervals	(mimic realtime).

       -t     Print a timestamp	in  the	 form  of  YYYY/MM/DD  HH:MM:SS.UUUUUU
	      everytime	a packet is matched.

       -T     Print a timestamp	in the form of +S.UUUUUU, indicating the delta
	      between packet matches.

       -R     Do not try to drop privileges to the DROPPRIVS_USER.

	      ngrep makes no effort to validate	input  from  live  or  offline
	      sources  as it is	focused	more on	performance and	handling large
	      amounts of data than protocol correctness, which is most often a
	      fair assumption to make.	However, sometimes it matters and thus
	      as a rule	ngrep will try to be defensive and drop	any root priv-
	      ileges it	might have.

	      There  exist scenarios where this	behaviour can become an	obsta-
	      cle, so this option is provided to end-users who want to disable
	      this feature, but	must do	so with	an understanding of the	risks.
	      Packets can be randomly malformed	or even	specifically  designed
	      to overflow sniffers and take control of them, and revoking root
	      privileges is currently the only risk mitigation	ngrep  employs
	      against such an attack.  Use this	option and turn	it off at your
	      own risk.

       -c cols
	      Explicitly set the console width to ``cols''.  Note that this is
	      the  console  width, and not the full width of what ngrep	prints
	      out as payloads; depending on the	output mode  ngrep  may	 print
	      less than	``cols'' bytes per line	(indentation).

       -F file
	      Read  in	the bpf	filter from the	specified filename.  This is a
	      compatibility option for users familiar  with  tcpdump.	Please
	      note  that specifying ``-F'' will	override any bpf filter	speci-
	      fied on the command-line.

       -P char
	      Specify an alternate character to	signify	non-printable  charac-
	      ters when	displayed.  The	default	is ``.''.

       -W normal|byline|single|none
	      Specify  an alternate manner for displaying packets, when	not in
	      hexadecimal mode.	 The ``byline''	 mode  honors  embedded	 line-
	      feeds,  wrapping	text only when a linefeed is encountered.  The
	      ``none'' mode doesn't wrap under any circumstance	 (entire  pay-
	      load  is displayed on one	line).	The ``single'' mode is concep-
	      tually the same as ``none'', except that everything including IP
	      and  source/destination  header  information is all on one line.
	      ``normal'' is the	default	mode and is  only  included  for  com-
	      pleteness.  This option is incompatible with ``-x''.

       -s snaplen
	      Set the bpf caplen to snaplen (default 65536).

       -S limitlen
	      Set  the upper limit on the size of packets that ngrep will look
	      at.  Useful for looking at only the first	 N  bytes  of  packets
	      without changing the BPF snaplen.

       -I pcap_dump
	      Input file pcap_dump into	ngrep.	Works with any pcap-compatible
	      dump file	format.	 This option is	useful	for  searching	for  a
	      wide range of different patterns over the	same packet stream.

       -O pcap_dump
	      Output  matched  packets	to  a pcap-compatible dump file.  This
	      feature does not interfere with normal output to stdout.

       -n num Match only num packets total, then exit.

       -d dev By default ngrep will select a default interface to  listen  on.
	      Use this option to force ngrep to	listen on interface dev.

       -A num Dump num packets of trailing context after matching a packet.

       -W normal|byline|none
	      Alter the	method by which	ngrep displays packet payload.	``nor-
	      mal''  mode  represents  the  standard   behaviour,   ``byline''
	      instructs	 ngrep	to  respect  embedded  linefeeds  (useful  for
	      observing	HTTP transactions, for instance), and ``none'' results
	      in  the payload on one single line (useful for scripted process-
	      ing of ngrep output).

       -c cols
	      Ignore the detected terminal width and force the column width to
	      the specified size.

       -P char
	      Change the non-printable character from the default ``.''	to the
	      character	specified.

	match expression
	      A	match expression is either an extended regular expression,  or
	      if the -X	option is specified, a string signifying a hexadecimal
	      value.  An extended regular  expression  follows	the  rules  as
	      implemented  by  the GNU regex library.  Hexadecimal expressions
	      can optionally be	preceded by `0x'.  E.g., `DEADBEEF',  `0xDEAD-

	bpf filter
	      Selects a	filter that specifies what packets will	be dumped.  If
	      no bpf filter is given, all IP  packets  seen  on	 the  selected
	      interface	will be	dumped.	 Otherwise, only packets for which bpf
	      filter is	`true' will be dumped.

       The bpf filter consists of one or more primitives.  Primitives  usually
       consist	of  an id (name	or number) preceded by one or more qualifiers.
       There are three different kinds of qualifier:

       type   qualifiers say what kind of thing	the id name or	number	refers
	      to.  Possible types are host, net	and port.  E.g., `host blort',
	      `net 1.2.3', `port 80'.  If there	is no type qualifier, host  is

       dir    qualifiers  specify  a  particular  transfer direction to	and/or
	      from id.	Possible directions are	src, dst, src or dst  and  src
	      and  dst.	  E.g.,	 `src  foo', `dst net 1.2.3', `src or dst port
	      ftp-data'.  If there is no dir qualifier,	src or dst is assumed.
	      For  `null'  link	 layers	(i.e. point to point protocols such as
	      slip) the	inbound	and outbound qualifiers	can be used to specify
	      a	desired	direction.

       proto  qualifiers are restricted	to ip-only protocols.  Possible	protos
	      are: tcp , udp and icmp.	e.g., `udp src foo' or `tcp port  21'.
	      If  there	 is  no	proto qualifier, all protocols consistent with
	      the type are assumed.  E.g., `src	foo' means `ip	and  ((tcp  or
	      udp)  src	 foo)',	 `net bar' means `ip and (net bar)', and `port
	      53' means	`ip and	((tcp or udp) port 53)'.

       In addition to the above, there are some	special	 `primitive'  keywords
       that  don't  follow  the	pattern: gateway, broadcast, less, greater and
       arithmetic expressions.	All of these are described below.

       More complex filter expressions are built up by using the words and, or
       and  not	to combine primitives.	E.g., `host blort and not port ftp and
       not port	ftp-data'.  To save typing, identical qualifier	lists  can  be
       omitted.	 E.g., `tcp dst	port ftp or ftp-data or	domain'	is exactly the
       same as `tcp dst	port ftp or tcp	dst port  ftp-data  or	tcp  dst  port

       Allowable primitives are:

       dst host	host
	      True  if	the  IP	destination field of the packet	is host, which
	      may be either an address or a name.

       src host	host
	      True if the IP source field of the packet	is host.

       host host
	      True if either the IP source or destination  of  the  packet  is
	      host.   Any  of the above	host expressions can be	prepended with
	      the keywords, ip,	arp, or	rarp as	in:
		   ip host host
	      which is equivalent to:

       ether dst ehost
	      True if the ethernet destination address is ehost.  Ehost	may be
	      either  a	 name from /etc/ethers or a number (see	ethers(3N) for
	      numeric format).

       ether src ehost
	      True if the ethernet source address is ehost.

       ether host ehost
	      True if either the ethernet source  or  destination  address  is

       gateway host
	      True  if	the packet used	host as	a gateway.  I.e., the ethernet
	      source or	destination address was	host but neither the IP	source
	      nor  the	IP destination was host.  Host must be a name and must
	      be found in both /etc/hosts  and	/etc/ethers.   (An  equivalent
	      expression is
		   ether host ehost and	not host host
	      which  can  be  used  with  either  names	 or numbers for	host /

       dst net net
	      True if the IP destination address of the	packet has  a  network
	      number  of net. Net may be either	a name from /etc/networks or a
	      network number (see networks(4) for details).

       src net net
	      True if the IP source address of the packet has a	network	number
	      of net.

       net net
	      True  if	either	the  IP	 source	 or destination	address	of the
	      packet has a network number of net.

       net net mask mask
	      True if the IP address matches net with  the  specific  netmask.
	      May be qualified with src	or dst.

       net net/len
	      True if the IP address matches net a netmask len bits wide.  May
	      be qualified with	src or dst.

       dst port	port
	      True if the packet is ip/tcp or ip/udp  and  has	a  destination
	      port  value of port.  The	port can be a number or	a name used in
	      /etc/services (see tcp(4P) and udp(4P)).	If  a  name  is	 used,
	      both  the	 port number and protocol are checked.	If a number or
	      ambiguous	name is	used, only the port number is  checked	(e.g.,
	      dst port 513 will	print both tcp/login traffic and udp/who traf-
	      fic, and port domain will	print both tcp/domain  and  udp/domain

       src port	port
	      True if the packet has a source port value of port.

       port port
	      True  if	either the source or destination port of the packet is
	      port.  Any of the	above port expressions can be  prepended  with
	      the keywords, tcp	or udp,	as in:
		   tcp src port	port
	      which matches only tcp packets whose source port is port.

       less length
	      True  if	the  packet has	a length less than or equal to length.
	      This is equivalent to:
		   len <= length.

       greater length
	      True if the packet has a length greater than or equal to length.
	      This is equivalent to:
		   len >= length.

       ip proto	protocol
	      True if the packet is an ip packet (see ip(4P)) of protocol type
	      protocol.	 Protocol can be a number or one of the	names tcp, udp
	      or  icmp.	  Note	that the identifiers tcp and udp are also key-
	      words and	must be	escaped	via backslash (\), which is \\ in  the

       ip broadcast
	      True  if	the  packet  is	an IP broadcast	packet.	 It checks for
	      both the all-zeroes  and	all-ones  broadcast  conventions,  and
	      looks up the local subnet	mask.

       ip multicast
	      True if the packet is an IP multicast packet.

       ip     Abbreviation for:
		   ether proto ip

       tcp, udp, icmp
	      Abbreviations for:
		   ip proto p
	      where p is one of	the above protocols.

       expr relop expr
	      True  if the relation holds, where relop is one of >, <, >=, <=,
	      =, !=, and expr is an arithmetic expression composed of  integer
	      constants	 (expressed  in	 standard C syntax), the normal	binary
	      operators	[+, -, *, /, &,	|], a  length  operator,  and  special
	      packet  data  accessors.	 To access data	inside the packet, use
	      the following syntax:
		   proto [ expr	: size ]
	      Proto is one of ip, tcp, udp or icmp, and	indicates the protocol
	      layer for	the index operation.  The byte offset, relative	to the
	      indicated	protocol layer,	is given by expr.   Size  is  optional
	      and  indicates  the number of bytes in the field of interest; it
	      can be either one, two, or  four,	 and  defaults	to  one.   The
	      length  operator,	indicated by the keyword len, gives the	length
	      of the packet.

	      For example, `ether[0] & 1 != 0' catches all multicast  traffic.
	      The  expression  `ip[0]  & 0xf !=	5' catches all IP packets with
	      options. The expression `ip[6:2] &  0x1fff  =  0'	 catches  only
	      unfragmented  datagrams  and  frag zero of fragmented datagrams.
	      This check is implicitly applied to the tcp and udp index	opera-
	      tions.   For instance, tcp[0] always means the first byte	of the
	      TCP header, and never means the first  byte  of  an  intervening

       Primitives may be combined using:

	      A	 parenthesized	group of primitives and	operators (parentheses
	      are special to the Shell and must	be escaped).

	      Negation (`!' or `not').

	      Concatenation (`&&' or `and').

	      Alternation (`||'	or `or').

       Negation	has highest precedence.	 Alternation  and  concatenation  have
       equal  precedence  and associate	left to	right.	Note that explicit and
       tokens, not juxtaposition, are now required for concatenation.

       If an identifier	is given without a keyword, the	most recent keyword is
       assumed.	 For example,
	    not	host vs	and ace
       is short	for
	    not	host vs	and host ace
       which should not	be confused with
	    not	( host vs or ace )

       Expression arguments can	be passed to ngrep as either a single argument
       or as multiple arguments, whichever is more convenient.	Generally,  if
       the  expression	contains Shell metacharacters, it is easier to pass it
       as a single, quoted argument.  Multiple arguments are concatenated with
       spaces before being parsed.

       Errors from ngrep, libpcap, and the GNU regex library are all output to

       Written by Jordan Ritter	<>.

       Please report bugs to the ngrep's Sourceforge Bug Tracker, located at

       Non-bug,	non-feature-request general feedback should  be	 sent  to  the
       author directly by email.


*nux				 November 2006			      NGREP(8)


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