icmp(n) 							 Tnm Tcl Extension							   icmp(n)

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NAME

       icmp - Send ICMP messages to hosts on the Internet.
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DESCRIPTION

       The  icmp command allows to send Internet Control Messages (ICMP) (RFC 792, RFC 1122) to a list of hosts on the Internet. ICMP messages can
       be used to check whether hosts are reachable. The icmp command can also be used to trace routes to Internet hosts by sending UDP  datagrams
       to unused UDP ports and interpreting the ICMP responses (Van Jacobsen and Steve Deering algorithm).

ICMP COMMAND

       The  icmp  command  always  accepts  a list of target hosts. ICMP messages are send to the targets in a round-robin fashion which allows to
       check entire IP address ranges or a list of core routers efficiently. The user of the icmp command should be careful not to flood a network
       with ICMP requests.

       icmp [options]
	      Invoking	the  icmp command with options but without any command arguments allows to retrieve and change the default values. See the
	      description of supported options below. Default values are bound to a Tcl interpreter which allows to have multiple Tcl  interpreter
	      with different defaults.

       icmp [options] echo hosts
	      The  icmp  echo  command can be used to test the reachability of IP devices by sending ICMP echo requests to the hosts.  The command
	      returns a list of host / round trip time pairs. The round trip time is returned in milliseconds. A negative round  trip  time  indi-
	      cates that a host did not respond in the timeout interval.

       icmp [options] mask hosts
	      The icmp mask command sends ICMP mask requests and returns a list of host / netmask pairs. The mask will be set to 0.0.0.0 if a host
	      does not respond to ICMP mask requests.

       icmp [options] timestamp hosts
	      The icmp timestamp command retrieves timestamps using the ICMP timestamp request. This command returns an estimate of the time  dif-
	      ference  between	local  time  and the time on the hosts given in hosts. The command returns a list of host / time offset pairs. The
	      time offset is returned in milliseconds. An empty time offset indicates that a host did not respond in the timeout interval.

       icmp [options] ttl num hosts
	      The icmp ttl command, which may not be supported on every operating system, sends a UDP packet to an unused  port  number  with  the
	      time  to	live field of the IP header set to num. This command returns a list of host / round trip time pairs, where the host is the
	      IP device being num hops away. The round trip time is returned in milliseconds. A negative round trip time indicates that a host did
	      not respond in the timeout interval.

       icmp [options] trace num hosts
	      The  icmp trace command works similar to the icmp ttl command but it always returns the destination address even when the responding
	      host chooses another interface with a different IP address to send the reply. This can be used to trace a route to a host since  the
	      command returns the host that discards the packet if it does not reach the destination.

ICMP OPTIONS

       The following options control how ICMP requests are send and how the icmp command deals with lost ICMP packets.

       -timeout time
	      The  -timeout  option defines the time the icmp command will wait for a response. The time is defined in seconds with a default of 5
	      seconds.

       -retries number
	      The -retries option defines how many times a request is retransmitted during the timeout interval. The default number of retries	is
	      2.

       -delay time
	      The  -delay  option  defines  the  minimum delay between two outgoing ICMP packets. The delay time is defined in milliseconds with a
	      default delay of 0 milliseconds. Delays are useful to reduce the load on intermediate devices like gateways or bridges.

       -size number
	      The -size option allows to control the size of ICMP packets. The number defines the size of ICMP packets in  bytes  with	a  default
	      size of 64 bytes. Sizes smaller than 64 bytes are silently rounded to 64 bytes.

BUGS

       The  icmp  command requires the setuid root program ntping(8) because sending icmp packets requires access to raw sockets on most operating
       systems.

SEE ALSO

       scotty(1), ntping(8), Tnm(n), Tcl(n)

AUTHORS

       Juergen Schoenwaelder <schoenw@cs.utwente.nl>

Tnm																	   icmp(n)