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                               September 2017



 NAME
      ngrep - network grep


 SYNOPSIS
      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 >


 DESCRIPTION
      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
      payloads of packets.  It currently recognizes TCP, UDP and ICMP across
      Ethernet, PPP, SLIP, FDDI and null interfaces, and understands bpf
      filter logic in the same fashion as more common packet sniffing tools,
      such as tcpdump(8) and snoop(1).



 OPTIONS
      -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.





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      -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 expression.


      -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.  Specify a second time to indicate the
           delta since the first packet match.


      -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
           privileges it might have.

           There exist scenarios where this behaviour can become an
           obstacle, 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



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           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
           specified on the command-line.


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


      -K num
           Kill matching TCP connections (like tcpkill).  The numeric
           argument controls how many RST segments are sent.


      -W normal|byline|single|none
           Specify an alternate manner for displaying packets, when not in
           hexadecimal mode.  The ``byline'' mode honors embedded linefeeds,
           wrapping text only when a linefeed is encountered (useful for
           observing HTTP transactions, for instance).  The ``none'' mode
           doesn't wrap under any circumstance (entire payload is displayed
           on one line).  The ``single'' mode is conceptually 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
           completeness.  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.




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      -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.


       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',
           `0xDEADBEEF'.


       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
           assumed.

      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.




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      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 domain'.  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
           ehost.





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      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 / ehost.)


      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
           traffic, and port domain will print both tcp/domain and
           udp/domain traffic).


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



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      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 keywords
           and must be escaped via backslash (\), which is \\ in the C-
           shell.


      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



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           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
           operations.  For instance, tcp[0] always means the first byte of
           the TCP header, and never means the first byte of an intervening
           fragment.  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.


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



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      to stderr.


 EXIT STATUS
      The ngrep utility exits with one of the following values:

           0     One or more frames were matched.
           1     No frames were matched.
           2     An error occurred.
           3+    Hell is freezing over, run!


 AUTHOR
      Written by Jordan Ritter <jpr5@darkridge.com>.


 REPORTING BUGS
      Please report bugs to the ngrep's GitHub Issue Tracker, located at

          http://github.com/jpr5/ngrep/issues

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


 NOTES
      ALL YOUR BASE ARE BELONG TO US.

























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