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Manpages Net::PingSection: Perl Programmers Reference Guide (3perl)Updated: 2001-02-22 Index Return to Main Contents NAMENet::Ping - check a remote host for reachabilitySYNOPSISuse Net::Ping; $p = Net::Ping->new(); print "$host is alive.\n" if $p->ping($host); $p->close(); $p = Net::Ping->new("icmp"); foreach $host (@host_array) { print "$host is "; print "NOT " unless $p->ping($host, 2); print "reachable.\n"; sleep(1); } $p->close(); $p = Net::Ping->new("tcp", 2); while ($stop_time > time()) { print "$host not reachable ", scalar(localtime()), "\n" unless $p->ping($host); sleep(300); } undef($p); # For backward compatibility print "$host is alive.\n" if pingecho($host); DESCRIPTIONThis module contains methods to test the reachability of remote hosts on a network. A ping object is first created with optional parameters, a variable number of hosts may be pinged multiple times and then the connection is closed.You may choose one of three different protocols to use for the ping. The ``udp'' protocol is the default. Note that a live remote host may still fail to be pingable by one or more of these protocols. For example, www.microsoft.com is generally alive but not pingable. With the ``tcp'' protocol the ping() method attempts to establish a connection to the remote host's echo port. If the connection is successfully established, the remote host is considered reachable. No data is actually echoed. This protocol does not require any special privileges but has higher overhead than the other two protocols. Specifying the ``udp'' protocol causes the ping() method to send a udp packet to the remote host's echo port. If the echoed packet is received from the remote host and the received packet contains the same data as the packet that was sent, the remote host is considered reachable. This protocol does not require any special privileges. It should be borne in mind that, for both tcp and udp ping, a host will be reported as unreachable if it is not running the appropriate echo service. For Unix-like systems see inetd(8) for more information. If the ``icmp'' protocol is specified, the ping() method sends an icmp echo message to the remote host, which is what the UNIX ping program does. If the echoed message is received from the remote host and the echoed information is correct, the remote host is considered reachable. Specifying the ``icmp'' protocol requires that the program be run as root or that the program be setuid to root. Functions
WARNINGpingecho() or a ping object with the tcp protocol use alarm() to implement the timeout. So, don't use alarm() in your program while you are using pingecho() or a ping object with the tcp protocol. The udp and icmp protocols do not use alarm() to implement the timeout.NOTESThere will be less network overhead (and some efficiency in your program) if you specify either the udp or the icmp protocol. The tcp protocol will generate 2.5 times or more traffic for each ping than either udp or icmp. If many hosts are pinged frequently, you may wish to implement a small wait (e.g. 25ms or more) between each ping to avoid flooding your network with packets.The icmp protocol requires that the program be run as root or that it be setuid to root. The tcp and udp protocols do not require special privileges, but not all network devices implement the echo protocol for tcp or udp. Local hosts should normally respond to pings within milliseconds. However, on a very congested network it may take up to 3 seconds or longer to receive an echo packet from the remote host. If the timeout is set too low under these conditions, it will appear that the remote host is not reachable (which is almost the truth). Reachability doesn't necessarily mean that the remote host is actually functioning beyond its ability to echo packets. Because of a lack of anything better, this module uses its own routines to pack and unpack ICMP packets. It would be better for a separate module to be written which understands all of the different kinds of ICMP packets.
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