A fast and recursive DNS name resolver for log files
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   Application: jdresolve 0.6.2
   Author: [1]John D. Rowell
   Homepage: [2]https://github.com/jdrowell/jdresolve


   make install

   Try: jdresolve <log file> > <resolved file>
   i.e. jdresolve access_log > resolved.log

   To use recursion, just use the "-r" command line option.


   jdresolve resolves IP addresses to hostnames. Any file format is
   supported, including those where the line does not begin with the IP
   address. One of the strongest features of the program is the support
   for recursion, which can drastically reduce the number of unresolved
   hosts by faking a hostname based on the network that the IP belongs to.
   DNS queries are sent in parallel, which means that you can decrease run
   time by increasing the number of simultaneous sockets used (given a
   fast enough machine and available bandwidth). By using the database
   support, performance can be increased even further, by using cached
   data from previous runs.


   jdresolve used the algorithms describe below up to version 0.2.

   The initial version of jdresolve tried to only speed up the name
   resolution by implementing numerous concurrent requests. I The first
   problem was: how to resolve the maximum possible number of IPs
   concurrently without reading the whole log file into memory (they can
   get quite _huge_)? I figured I'd need a 2 pass approach, collecting all
   distinct host IPs that needing resolving in the first step, then
   resolving them efficiently inside a loop, and finally just replacing
   the resolved IPs on the second pass through the log file.

   This way we can garantee that the resolve queue will always be full
   with no need to weight that against how many lines of buffered log
   entries we would need to cache. The number of distinct IP addresses
   tend to be quite lower than the number of lines in the log file, and
   the IP part takes about only 1/20th of the log line, so we can't be
   using too much memory just by putting a few hundred or thousand small
   strings into a hash.

   After looking thru [3]CPAN, I came across the excellent Net::DNS module
   and was more than happy to note that it already provide a subroutine
   and examples for background queries. Just add IO::Select to that and
   you have a full non-blocking aproach to multiple concurrent queries.
   You can even specify the timeouts to make the name resolving even more

   Having this much done, I was quite happy to have the fastest log
   resolving routine I have come accross. By setting the numbers of
   concurrent sockets and timeouts you could fine tune the beast to
   resolve names _very_ rapidly. But still there where about 25% of the
   IPs left unresolved...

   "This is not much help", I thought. I need to know _at least_ from what
   country these people are accessing from. After a few not very
   scientifical aproaches, I realized that by recurring thru the DNS
   classes (C, B and finally A) and checking for the host listed in the
   SOA record I could be pretty sure this was a father domain to the IP.
   The implementation goes like this: find out all distinct IP addresses,
   then determine which C, B and A classes contain these addresses. Make
   up a list from these queries and send them thru a resolver in chuncks
   of 32 (configurable via the command line). If a socket times out, leave
   that request unresolved.

   After running a big log file against the recursive aproach, I
   determined it didn't take much longer to resolve it at all. Full class
   domains tend to have decently configured DNS servers, and you get a lot
   of repeated classes when resolving your logs. The best was still to
   come: 0 unresolved IPs :) And since that I haven't found an IP that
   can't be determined at least to it's A class.


   The above algorithm works extremely well except for the case of very
   large logs (>100Mb). The hashes containing IPs and their parent A/B/C
   classes gets pretty huge doesn't fit in memory any more.

   So as of v0.3, we have a new 1 pass approach. We have a line cache that
   holds 10000 lines (configurable with -l, don't set it much lower).
   Using my test base it looks like each 10000 lines take about 4Mb of RAM
   during processing (that's the log lines themselves plus the hashes and
   arrays used for caching/processing). Each IP and class to be resolved
   has a count value, which is increased every time a line with that
   number is read, and decreased after we print out a resolved line with
   that reference value.

   Think of it as a "moving window" method, and that we do our own garbage
   collection. The process pauses if the first line in our line cache is
   still unresolved, we don't have any more sockets, or we're waiting for
   socket data. We can't control the last two items, but to minimize the
   pauses do to yet unresolved lines, increase the -l value if you notice
   pauses during resolving. There should be enough lines cached so that
   even if we have timeouts on sockets we are still waiting for other
   socket data to come in, not just for 1 single socket to time out.

   Using this method the memory usage during executing is almost constant.
   So you can determine how much RAM you wish to use for resolving names
   and set your -l value and forget about it. There's really no
   performance loss when compared to the <=v0.2 algorithm if you have a
   big enough line cache.


   Example: jdresolve access_log > resolved.log

   If you simply run the script as you would with the Apache logresolve
   program, you get the same results, only much faster. But if you want
   really take advantage of jdresolve, you should at least turn on the -r
   option for recursive resolves. As of version 0.2, the -m option takes a
   mask as an argument. The valid substitutions are %i for the IP address
   and %c for the resolved class. So an IP like with a mask of
   "%i.%c" (the default) would become something like
   "". A mask of "somewhere.in.%c" would turn it into

   The -h switch shows you basic help information. The -v switch will
   display version information. Use -d 1 or -d 2 (more verbose) to debug
   the resolving process and get extra statistics. If you don't care for
   the default statistics, use -n to disable them.

   After some runs you may want to change your timeout value. The -t
   option accepts a new value in seconds. For even better performance, use
   the -s switch with a value greater then 32, but remember that many
   operating systems have a hard coded default for open files of 256 or
   1024. Check your system's limit with "ulimit -a".

   New in v0.3 is the -l switch, which specified how many lines we will
   cache for resolving. The default is 10000, but can be vastly
   incremented without using too much RAM, as explained in "HOW IT WORKS".

   After you used jdresolve on the log file, you can check which ips where
   left unresolved by using the --unresolved option on the file that was


   'rhost' is a quick script to take advantage of the new STDIN
   functionality of jdresolve. Many times you use the 'host' command to
   resolve a single IP (like 'host'). As with standard log
   resolvers, 'host' doesn't do recursion. So 'rhost' just calls jdresolve
   with the apropriate parameters to resolve that single IP number. The
   syntax is 'rhost <ip>'.


   As of version 0.5, jdresolve provides simple database support thru db
   (dbm, gdbm, sdbm, etc) files. You can use the --database switch to
   specify the db file and that will allow for fallback in case some DNS
   servers are down and also performance improvements since you can lower
   your timeout value without sacrificing resolved percentage.

   To use the database support, just supply a database name (i.e.
   'hosts.db') using the --database option. If it does not yet exist, a
   new database with that name will be created. All resolved hosts and
   classes during a jdresolve run will be cached to the database.

   After you have some data in a db, you can use --dumpdb to look at it.
   With --mergedb to add new information to it (the format of the input
   file is the same as the one from a dump using --dumpdb, e.g. an
   ip/class followed by the hostname/classname, separated by white space)

   Ex: echo " testip" | jdresolve --database hosts.db --mergedb -
   ...adds and IP entry to the db
   Ex: echo "0.0.0 classname" | jdresolve --database hosts.db --mergedb -
   ...adds a class entry to the db

   Note: Since when recursing the resolved hostnames are stored to the
   database (even when resolved by recursion), you _may_ not want to use
   the same database for normal and recursed runs. That is because a
   cached host from a resolved run will show up as a "real" IP if you
   don't recurse and use the --dbfirst or --dbonly options, or just use
   the database and the lookup times out. Nothing too serious, but this
   detail may be important to some people.


   It seems that Net::DNS can perform suboptimally on non-Linux machines,
   even on *BSD (this is based on some bug reports I got from people using
   jdresolve in those environments). Also, on Windows NT (yes, some people
   still use that), you should make sure there is a 'resolv.conf' file
   somewhere (I'm no NT expert, read the docs). Since we use so little of
   the functionality of Net::DNS, I may replace it with standard sockets
   some time in the future. It is still a very very nice module though :)


   If you have dificulties using this program or would like to request a
   new feature, feel free to reach me at me@jdrowell.com.


   jdresolve is licensed under the GPL. See the COPYING file for details.


   1. mailto:me@jdrowell.com
   2. https://github.com/jdrowell/jdresolve
   3. http://www.cpan.org/