Troubleshooting Network V

Using traceroute


The traceroute utility is really cool. Remember that if you try to
send information to an IP host that doesn’t reside on your local
network segment, the packets will be sent to your default gateway
router. This router will then use a variety of routing protocols to
figure out how to get the packets to the destination system. In the
process, the packets may have to be transferred from router to router
to router to get them there. This is shown in Figure 15-16.



This is one of the beauties of an IP-based network. You can connect
multiple networks together using routers and transfer data between
them. It’s this functionality that allows the Internet to exist. You
can use a web browser to send http request packets to a web server
located somewhere in the world and have it respond with the web page
you want to view. The routing protocols used by routers dynamically
determine the best route for packets to take based on system load. The
route taken can change as network conditions change.



The traceroute utility can be used to trace the route a packet must
traverse through these routers to arrive at its destination. It does
this using the same ICMP echo request and ICMP echo response packets
used by the ping utility, but it manipulates the TTL parameter of
those packets. As a result, an ICMP echo response packet is sent back
to the source system from each router your packets cross as they work
their way through the network to the destination host, providing you
with a list that shows the route between the source and destination
systems.




This utility can be a very useful tool if you’re experiencing
communication problems between networks. The traceroute utility can
help you track down which router in the route isn’t working correctly.


The syntax for using this utility is



traceroute destination_hostname_or_IP_address



When you run it, traceroute creates one line for each router your packets cross as they
make their way to the destination system. This is shown in Figure 15-17.




As you can see in Figure 15-17, the IP address of the router is
displayed along with round-trip time statistics. As with the ping
command, you can also use the traceroute command with the IPv6
protocol. To do this, you run


  traceroute6


instead of traceroute.




NOTE

You can also use the


tracepath 


command to trace the route to a remote network host. The syntax, functionality, and
output are almost identical to traceroute. As with traceroute, you can run


tracepath6 


to use the IPv6 protocol with this command.









LX0-104 Exam Objectives (T)