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rwresolve(1)			SiLK Tool Suite			  rwresolve(1)

NAME
       rwresolve - Convert IP addresses	in delimited text to hostnames

SYNOPSIS
	 rwresolve [--ip-fields=FIELDS]	[--delimiter=C]	[--column-width=N]
	     [--resolver={ c-ares | adns | getnameinfo | gethostbyaddr }]
	     [--max-requests=N]

	 rwresolve --help

	 rwresolve --version

DESCRIPTION
       rwresolve is an application that	reads delimited	textual	input and maps
       IP addresses in the input to host names up performing a reverse DNS
       look-up.	 If the	look-up	succeeds, the IP is replaced with the host
       name (rwresolve uses the	first host name	returned by the	resolver).  If
       the look-up fails, the IP address remains unchanged.

       rwresolve does a	DNS query for every IP address,	so it can be extremely
       slow.  rwresolve	works best on very limited data	sets.  To reduce the
       number of DNS calls it makes, rwresolve caches the results of queries.
       There are two libraries that support asynchronous DNS queries which
       rwresolve can use if either of those libraries was found	when SiLK was
       configured.  These libraries are	the ADNS library and the c-ares
       library.	 Specify the --resolver	switch to have rwresolve use a
       particular function for look-ups.

       When an IP address resolves to multiple names, rwresolve	prints the
       first name returned by the resolver.

       rwresolve is designed specifically to deal with the output of rwcut(1),
       though it will work with	other SiLK tools that produce delimited	text.
       rwresolve reads the standard input, splits the line into	fields based
       on the delimiter	(default '|'), converts	the specified FIELDS (default
       fields 1	and 2) from an IP address in its canonical form	(e.g., dotted
       decimal for IPv4) to a hostname.	 If the	field cannot be	parsed as an
       address or if the look up fails to return a hostname, the field is not
       modified.  The fields to	convert	are specified via the
       --ip-fields=FIELDS option.  The --delimiter option can be used to
       specify an alternate delimiter.

       Since hostnames are generally wider than	IP addresses, the use of the
       --column-width field is advised to increase the width of	the IP
       columns.	 If this switch	is not specified, no justification of
       hostnames is attempted.

       By default, rwresolve will use the c-ares library if available, then it
       will use	the ADNS library if available.	To choose a different IP look
       up option, use the --resolver switch.

       The maximum number of parallel DNS queries to attempt with c-ares or
       ADNS can	be specified with the --max-requests switch.

OPTIONS
       Option names may	be abbreviated if the abbreviation is unique or	is an
       exact match for an option.  A parameter to an option may	be specified
       as --arg=param or --arg param, though the first form is required	for
       options that take optional parameters.

       --ip-fields=FIELDS
	   Specify the column number(s)	of the input that should be considered
	   IP addresses.  Column numbers start from 1.	If not specified, the
	   default is 1,2.

       --delimiter=C
	   Specify the character that separates	the columns of the input.  The
	   default is '|'.

       --column-width=WIDTH
	   Set the width of the	columns	specified in --ip-fields to WIDTH.
	   When	specified, the FIELDS columns always have the specified	WIDTH
	   regardless of whether the IP	to hostname mapping was	successful.
	   If this switch is not specified, fields containing IP addresses
	   that	could not be resolved will maintain their input	length,	and
	   fields where	the lookup was successful will be printed with no
	   padding.

       --resolver=c-ares
	   Use the c-ares library to convert the IP addresses to hostnames.
	   Requires that the c-ares library was	found when SiLK	was
	   configured.	This library supports IPv6 look-ups when SiLK is
	   compiled to support IPv6.

       --resolver=adns
	   Use the ADNS	library	to convert the IP addresses to hostnames.
	   Requires that the ADNS library was found when SiLK was configured.
	   This	library	only supports IPv4 look-ups.

       --resolver=getnameinfo
	   Use the getnameinfo(3) C library function to	convert	IP addresses
	   to hostnames.  This function	supports IPv6 look-ups when SiLK is
	   compiled to support IPv6.

       --resolver=gethostbyaddr
	   Use the gethostbyaddr(3) C library function to convert IP addresses
	   to hostnames.  This function	only supports IPv4.

       --max-requests=MAX
	   When	the c-ares or ADNS library is used, limit the number of
	   outstanding DNS queries active at any one time to MAX.  The default
	   is 128.  This switch	is not available if neither c-ares nor ADNS
	   were	found when SiLK	was compiled.

       --help
	   Print the available options and exit.

       --version
	   Print the version number and	information about how SiLK was
	   configured, then exit the application.

EXAMPLE
       In the following	examples, the dollar sign ("$")	represents the shell
       prompt.	The text after the dollar sign represents the command line.
       Lines have been wrapped for improved readability, and the back slash
       ("\") is	used to	indicate a wrapped line.

       Suppose you have	found some interesting data in the file
       interesting.rw, and you want to view the	data using rwcut(1), but you
       also want to determine the hostname of each the source IPs and append
       that hostname to	the rwcut output.  In the example command below, note
       how the source IP field (rwcut field 1) was specified twice in the
       rwcut invocation, and rwresolve is told to resolve the second
       occurrence, which is field in column 13.	 This allows you to see	the
       source IP (in the first column) and the host name it mapped to (in the
       final column).

	$ rwcut	--fields=1-12,1	interesting.rw		   \
	  | rwresolve --ip-field=13

ENVIRONMENT
       When ADNS is used, the following	environment variables affect it.  The
       ADNS_ form of each variable takes precedence.

       RES_CONF
       ADNS_RES_CONF
	   A filename, whose contents are in the format	of resolv.conf.

       RES_CONF_TEXT
       ADNS_RES_CONF_TEXT
	   A string in the format of resolv.conf.

       RES_OPTIONS
       ADNS_RES_OPTIONS
	   These are parsed as if they appeared	in the options line of a
	   resolv.conf.	 In addition to	being parsed at	this point in the
	   sequence, they are also parsed at the very beginning	before
	   resolv.conf or any other environment	variables are read, so that
	   any debug option can	affect the processing of the configuration.

       LOCALDOMAIN
       ADNS_LOCALDOMAIN
	   These are interpreted as if their contents appeared in a search
	   line	in resolv.conf.

SEE ALSO
       rwcut(1), silk(7), gethostbyaddr(3), getnameinfo(3)

BUGS
       Because rwresolve must do a DNS query for every IP address, it is
       extremely slow.

       The output from rwresolve is rarely columnar because hostnames can be
       very long.  You may want	to consider putting the	resolved hostnames in
       the final column	of output.

SiLK 3.15.0			  2017-07-02			  rwresolve(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXAMPLE | ENVIRONMENT | SEE ALSO | BUGS

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