NETSELECT(1)						      General Commands Manual						      NETSELECT(1)

NAME

       netselect - choose the fastest server automatically

SYNOPSIS

       netselect [-v|-vv|-vvv|-vvvv] [-m HOPS] [-s SERVERS] [-t PACKETS [-I] [-D] host ...

DESCRIPTION

       netselect  determines  several  facts about all of the hosts given on the command line, much faster than you would if you manually tried to
       use ping and traceroute.

       For each host, netselect figures out the approximate ping time (though not as accurately as ping does), the number  of  network	"hops"	to
       reach  the  target, and the percentage of ping requests that got through successfully. Then netselect calculates the "score" of each opera-
       tional host based on these values.  A lower score is better, in the end it prints one line showing the server with the best score.

       If the DNS name has multiple IP addresses associated with IT netselect will test each of the IP addresses independently. In this case, net-
       select will report the IP address of the fastest server (unless the -D option is used).

       If  the	number	of  found hosts is not the same as the number requested (using -s), netselect will emit a warning message. If no hosts are
       found at all, the program will also end with an error return value.

EXAMPLES

       # netselect -vv ftp.fceia.unr.edu.ar ftp.kulnet.kuleuven.ac.be 
		  ftp.cdrom.com ftp.debian.org ftp.de.debian.org

       This is the output:

       ftp.fceia.unr.edu.ar	    2792 ms  23 hops  100% ok ( 1/ 1) [ 9213]
       ftp.kulnet.kuleuven.ac.be    9999 ms  30 hops	0% ok
       ftp.cdrom.com		      94 ms   8 hops  100% ok (10/10) [  169]
       ftp.debian.org		      46 ms  15 hops  100% ok (10/10) [  115]
       ftp.de.debian.org	    9999 ms  30 hops	0% ok
	 115 ftp.debian.org

       The value in brackets is the "score" of each operational host based on these values.  A lower score is better.  The  last  line	shows  the
       server with the best score.  If we had not used '-vv' on the command line, only this last line would have been printed.

       Note  that  for	ftp.kulnet.kuleuven.ac.be  and ftp.de.debian.org in this case, nothing got through at all.  That indicates that either the
       host doesn't exist, or it is down.

       # netselect -vv http.us.debian.org

       This is the output:

       204.152.191.39		    300 ms  17 hops   90% ok ( 9/10) [	899]
       35.9.37.225		    9999 ms  30 hops	0% ok
       64.50.233.100		    9999 ms  30 hops	0% ok
       128.30.2.36		    183 ms  15 hops   90% ok ( 9/10) [	510]
       149.20.20.135		    226 ms  18 hops   90% ok ( 9/10) [	702]
	 510 128.30.2.36

       In this case, since the single name has multiple DNS addresses all of the servers will be tested independently and the fastest server  will
       be provided.

       If you notice the above output you will see that the time for some hosts is 9999 ms. This is typically an indication of remote hosts block-
       ing the UDP probes netselect relies on. To prevent this issue you can use ICMP tests. For example, repeating the  above	test  using  ICMP,
       that is:

       # netselect -I -vv http.us.debian.org

       yields the following output:

       204.152.191.39		    291 ms  17 hops  100% ok (10/10) [	785]
       35.9.37.225		    180 ms  19 hops   66% ok ( 2/ 3) [	783]
       64.50.233.100		    140 ms  12 hops  100% ok (10/10) [	308]
       128.30.2.36		    182 ms  15 hops  100% ok (10/10) [	455]
       149.20.20.135		    227 ms  18 hops  100% ok (10/10) [	635]
	 308 64.50.233.100

       In this last example the selected server will change since, actually, the fastest server is one that also actively blocks UDP probes.

       You  can  also  use the tag feature based on postpending the server name with itself so the result includes both the fastest IP address and
       the original server name. For example, running a query with tags such as this one:

       # netselect -I -vv http.us.debian.org:http.us.debian.org

       will yield output similar to:

       35.9.37.225:http.us.debian.org	     9999 ms  30 hops	 0% ok
       64.50.233.100:http.us.debian.org      9999 ms  30 hops	 0% ok
       64.50.236.52:http.us.debian.org	     9999 ms  30 hops	 0% ok
       128.30.2.36:http.us.debian.org	      189 ms  14 hops	90% ok ( 9/10) [  504]
       199.6.12.70:http.us.debian.org	      286 ms  17 hops	90% ok ( 9/10) [  858]
	 504 128.30.2.36:http.us.debian.org

       Or you can use the -D option to force netselect to print out only DNS names. For example:

       # netselect -I -vv -D ftp.us.debian.org ftp.ru.debian.org

       will yield output similar to:

       128.30.2.36		    186 ms  14 hops  100% ok (10/10) [	446]
       199.6.12.70		    294 ms  17 hops   87% ok ( 7/ 8) [	907]
       35.9.37.225		    177 ms  19 hops   66% ok ( 2/ 3) [	768]
       64.50.233.100		    141 ms  12 hops  100% ok (10/10) [	310]
       64.50.236.52		    162 ms  13 hops  100% ok (10/10) [	372]
       ftp.ru.debian.org	    112 ms  18 hops  100% ok (10/10) [	313]
	 310 ftp.us.debian.org

       As you can see here, netselect will select a DNS name (in the example 'ftp.us.debian.org') which associated with multiple IP addresses over
       other  servers  as long as there is one server in the pool faster than others. However, using the DNS name for a server configuration might
       lead to actually  slower  throughput  if,  on  average,	the  different	IP  addresses  are  not  as  responsive.  In  the  above  example,
       'ftp.ru.debian.org' is second on the list and might be a better option (again, on average) than 'ftp.us.debian.org'.

OPTIONS

       -v     Verbose  mode.  Displays nameserver resolution messages to stderr.  You probably want this so that you don't get bored waiting for a
	      hundred name resolutions to finish.

       -vv    Very verbose mode.  Displays nameserver resolution and statistics (not just scores) to STDERR and STDOUT.

       -vvv   Very very verbose mode.  Everything -vv prints, plus it print every packet received as it happens.  Good for debugging or trying	to
	      figure out how it works.

       -vvvv  Very very very verbose mode.  Everything -vvv prints, plus a trace of all packets sent.

       -m HOPS
	      Maximum TTL (time to live).  Don't accept hosts that are further than HOPS away.

       -s SERVERS
	      Print this many "top-scoring" SERVERS at the end of the list.  If SERVERS is 0, then this disables printing of high scores.

       -t PACKETS
	      Make  sure  at  least  50%  of  the  hosts  get  tested with this many PACKETS.  The more packets you use, the more accurate are the
	      results... and the longer it takes to run.  The default is 10, which is usually okay.

       -I     Use ICMP instead of UDP probes. On some occasions (e.g. firewalled hosts) UDP probes like those used in traceroute will get filtered
	      out and hosts might be perceived as dead. Using this option will make netselect use ICMP probes instead.

       -D     netselect  provides the IP address of the servers that are tested if the name resolves to more than one address (i.e. the remote end
	      is using DNS round-robin). This makes it easier to spot which is the fastest server of a pool but might not be useful if you wish to
	      configure  a  system daemon with the DNS name or if the remote service does not accept calls to its IP address (as some HTTP servers
	      do). This option forces netselect to present the final server list using the original DNS name instead of the IP address if the  DNS
	      name resolves to more than one IP address.

SEE ALSO

       ping(8), traceroute(8), netselect-apt(1).

AUTHOR

       Avery Pennarun <apenwarr@gmail.com>

DEBIAN
								  March 14, 2004						      NETSELECT(1)