icmp(n) Tnm Tcl Extension icmp(n)_________________________________________________________________NAMEicmp - Send ICMP messages to hosts on the Internet.
_________________________________________________________________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 sup-
ported 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 indicates 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 difference between
local time and the time on the hosts given in
hosts. The command returns a list of host / time
Tnm 1
icmp(n) Tnm Tcl Extension icmp(n)
offset pairs. The time offset is returned in mil-
liseconds. 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 neg-
ative 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 desti-
nation.
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 com-
mand 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 inter-
val. 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 pack-
ets in bytes with a default size of 64 bytes. Sizes
smaller than 64 bytes are silently rounded to 64
bytes.
Tnm 2
icmp(n) Tnm Tcl Extension icmp(n)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 ALSOscotty(1), ntping(8), Tnm(n), Tcl(n)AUTHORS
Juergen Schoenwaelder <schoenw@cs.utwente.nl>
Tnm 3
