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TraceRoute is a tool that
traces the route (the specific gateway computers at each hop) from
a client machine to the remote host being contacted by reporting
all the router IP addresses in between. It also calculates and
displays the amount of time each hop took. TraceRoute is a handy
tool for both understanding where problems exist in the Internet
network and for getting a detailed sense of the Internet
itself.
TraceRoute works by causing
each router along a network path to return an Internet Control
Message Protocol (ICMP) error message. An IP packet contains a
Time-To-Live (TTL) value, which specifies how long it can go on its
search for a destination before being discarded. Each time a packet
passes through a router, its TTL value is decremented by one; when
it reaches zero, the packet is dropped, and an ICMP
TTL expired
in transit error message
is returned to the sender.
The TraceRoute program sends
its first group of packets with a TTL value of one. The first
router along the path will therefore discard the packet (its TTL is
decremented to zero) and return the TTL expired in
transit error. Thus, we
have found the first router on the path. Packets can then be sent
with a TTL of two, and then three, and so on, causing each router
along the path to return an error, identifying it to us. Some
routers silently drop packets with expired TTL; for such hops you
will get the Request timed
out error. Eventually,
either the final destination is reached, or the maximum value is
reached, and the TraceRoute ends. At the final destination,
TraceRoute sends an ICMP Echo Request packet (ping), and if the
destination computer is reachable, TraceRoute displays
Echo
reply in the Response
Message column.
To use this tool, enter an IP
address or hostname and click Start. The following options are
available:
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Start hop
– allows you to set the hop
from which to start tracing. It is often useful to set a value
higher than 1 if the first several hops of the route are always the
same; by setting a higher value you can save some time. |
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End hop
– allows you to limit the
number of hops to trace. |
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Pkt. size
– sets the size (in bytes) of
the data portion of the ICMP packet. |
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Timeout
– sets the maximum time (in
seconds) TraceRoute will wait for the response from a
router. |
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DNS resolving
– check this box if you want
TraceRoute to resolve IP addresses to hostnames. |
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Don't fragment
– sets the Don't fragment
flag in the packet. |
Right-clicking on the window
brings up a menu with the following commands:
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Send To
– sends the selected IP address
to other tools or to SmartWhois. |
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Copy Results
– copies the TraceRoute table
to the clipboard. |
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Save – saves the TraceRoute table to a
file. |
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