Objectives
Part 1: Determine Network
Connectivity to a Destination Host
Part 2: Trace a Route to a Remote
Server Using Tracert
Background / Scenario
Route tracing computer software lists the
networks that data traverses from the user’s originating end device to a
distant destination device.
This network tool is typically executed
at the command line as:
tracert
<destination network name or end device address>
(Microsoft Windows systems)
or
traceroute
<destination network name or end device address>
(UNIX, Linux systems, and Cisco devices,
such as switches and routers)
Both tracert
and traceroute determine the route
taken by packets across an IP network.
The tracert
(or traceroute) tool is often used
for network troubleshooting. By showing a list of routers traversed, the user can
identify the path taken to reach a particular destination on the network or
across internetworks. Each router
represents a point where one network connects to another network and through
which the data packet was forwarded. The number of routers is known as
the number of hops the data traveled from source to destination.
The displayed list can help identify data
flow problems when trying to access a service such as a website. It can also be
useful when performing tasks, such as downloading data. If there are multiple
websites (mirrors) available for the same data file, one can trace each mirror
to get a good idea of which mirror would be the fastest to use.
Command-line based route tracing tools
are usually embedded with the operating system of the end device. This activity
should be performed on a computer that has Internet access and access to a
command line.
Required Resources
PC with Internet access
Part 1:
Determine Network Connectivity
to a Destination Host
To trace the route to a distant network,
the PC used must have a working connection to the Internet. Use the ping command to test whether a host is
reachable. Packets of information are sent to the remote host with instructions
to reply. Your local PC measures whether a response is received to each packet,
and how long it takes for those packets to cross the network.
a.
At the command-line prompt,
type ping www.cisco.com to determine
if it is reachable.
b.
Now ping one of the Regional
Internet Registry (RIR) websites located in different parts of the world to
determine if it is reachable:
Africa: www.afrinic.net
Australia: www.apnic.net
South America: www.lacnic.net
North America: www.arin.net
Note: At the time of
writing, the European RIR www.ripe.net does
not reply to ICMP echo requests.
The website you selected will be used in
Part 2 for use with the tracert command.
Part 2:
Trace a Route to a Remote
Server Using Tracert
After you determine if your chosen
websites are reachable by using ping,
you will use tracert to determine
the path to reach the remote server. It is helpful to look more closely at each
network segment that is crossed.
Each hop in the tracert results displays the routes that the packets take when
traveling to the final destination. The PC sends three ICMP echo request
packets to the remote host. Each router in the path decrements the time to live
(TTL) value by 1 before passing it onto the next system. When the decremented
TTL value reaches 0, the router sends an ICMP Time Exceeded message back to the
source with its IP address and the current time. When the final destination is
reached, an ICMP echo reply is sent to the source host.
For example, the source host sends three
ICMP echo request packets to the first hop (192.168.1.1) with the TTL value of
1. When the router 192.168.1.1 receives the echo request packets, it decrements
the TTL value to 0. The router sends an ICMP Time Exceeded message back to the
source. This process continues until the source hosts sends the last three ICMP
echo request packets with TTL values of 8 (hop number 8 in the output below),
which is the final destination. After the ICMP echo request packets arrive at
the final destination, the router responds to the source with ICMP echo
replies.
For hops 2 and 3, these IP addresses are
private addresses. These routers are the typical setup for point-of-presence
(POP) of ISP. The POP devices connect users to an ISP network.
A web-based whois tool is found at http://whois.domaintools.com/. It is
used to determine the domains traveled from the source to destination.
a.
At the command-line prompt, trace
the route to www.cisco.com. Save the tracert output in a text file. Alternatively,
you can redirect the output to a text file by using > or >>.
C:\Users\User1> tracert www.cisco.com
or
C:\Users\User1> tracert www.cisco.com >
tracert-cisco.txt
Tracing
route to e144.dscb.akamaiedge.net [23.67.208.170]
over a
maximum of 30 hops:
1 1
ms <1 ms <1 ms
192.168.1.1
2 14
ms 7 ms 7 ms
10.39.0.1
3 10
ms 8 ms 7 ms
172.21.0.118
4 11
ms 11 ms 11 ms
70.169.73.196
5 10
ms 9 ms 11 ms
70.169.75.157
6 60
ms 49 ms *
68.1.2.109
7 43
ms 39 ms 38 ms
Equinix-DFW2.netarch.akamai.com [206.223.118.102]
8 33
ms 35 ms 33 ms
a23-67-208-170.deploy.akamaitechnologies.com [23.67.208.170]
Trace
complete.
b.
The web-based tool at http://whois.domaintools.com/ can be
used to determine the owners of both the resulting IP address and domain names shown
in the tracert tools output. Now perform a tracert
to one of RIR web sites from Part 1 and save the results.
Africa: www.afrinic.net
Australia: www.apnic.net
Europe: www.ripe.net
South America: www.lacnic.net
North America: www.arin.net
List the domains below from your tracert
results using the web-based whois tool.
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c.
Compare the lists of domains
crossed to reach the final destinations.
Reflection
What can affect tracert results?
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