Transcript assignment2 - La Salle University

Ping and traceroute
Lab/Homework exercise
Assigned 9/12/2006
Due 9/19/2006
CSIT 220 Fall, 2006
Based on T. Blum Exercises
Exercise/Assignment
• Assigned 9/12/2006
• We will be doing parts of this exercise in class.
• Some parts will require outside research and
reference.
• You need to submit the results of this exercise in a
hardcopy format.
• The lab exercise is due 9/19/2006. It will count as
a homework grade.
Pinging
• Ping is short for Packet Internet Groper
• It is a utility that sends a message to a computer
and waits for a response
– A utility is part of system software that is used to help
manage the computer’s resources, as opposed to
application software
• If the response is received, information about the
times required and so on are reported
• If the response is not received in a certain amount
of time, the request is said to have “timed out”
Pinging (Cont.)
• It works by sending special packets [ICMP
(Internet Control Message Protocol) echo request
and echo reply packets] to a destination, an IP
address or domain name
• If the destination responds, you have a good
TCP/IP connection (working route).
• There are many freeware and shareware PING
utilities available for personal computers (see for
example http://www.shareware.com)
Breaking it down
• Pinging consists of the command “ping”
followed by an IP address or domain name
– ping 139.84.10.250
– ping www.lasalle.edu
• It sends out special packets which request a
response (echo reply) if the destination host
is reached
host
• A computer that is connected to a TCP/IP
network, including the Internet.
• Each host has a unique IP address.
– A computer may always have the same address
or may have a different address each time it
connects to the networks
– Two computers on the same network or internet
at the same time should not have the same
address
Usual form
• Instead of writing out a string of thirty-two
1’s and 0’s, IP addresses are usually written
as four numbers between 0 and 255
separated by periods (the dotted decimal
notation)
• For example
139.84.10.250
How many?
• With 32 bits, 232 devices could be
distinguished
• Actually the number of valid IP addresses is
less than 232 because certain addresses are
reserved for special purposes (127.0.0.1 is
one example we’ll see later)
– Another problem is that addresses are “owned”
by people not using them
IP Address (cont.)
• In an isolated network, any set of IP
addresses can be assigned.
• On the other hand, connecting a network to
the Internet requires using registered IP
addresses to avoid duplications.
• The InterNIC Registration Service assigns
Internet addresses.
Domain name
• A domain name is a string of characters standing
in for an IP address
• Can have
– One Name  Multiple Addresses
– One Address  Multiple Names
• Domain names are used in URLs to identify
particular Web pages. For example, in the URL
http://www.pcwebopedia.com/index.html, the
domain name is pcwebopedia.com.
Packet
• A packet is a message (protocol + “some”
data) or a piece of a message transmitted
over a packet-switching network.
• A packet must also contain an address
(identifier) so that it can be routed to its
destination.
Packet switching
• A set of protocols (rules for communication) in
which messages are broken into pieces called
packets before being sent.
• The packets are transmitted individually
(connectionless).
– They may follow different routes
– They can arrive out of order
– Share the medium with other packets from other
transmissions
• When the packets arrive, they are reassembled into
the original message.
Pinging: Start/Run
Pinging: Type command in Run
dialog box
Actually cmd is preferred
Pinging: type ping followed by
domain name
Pinging a host which was off at
the time
Timed out
Can use IP instead of domain name
Pinging webopedia, also timed
out
Webopedia ping timed out, even
though site was up
Denial of service
• One possibility is that some companies
block pings because their systems could
become clogged with ping requests.
• Rejecting pings could make a site less
vulnerable to a Denial of Service (DoS)
attack, in which a site is flooded with so
many requests that it cannot answer them
all.
Ping Exercise Part 1 (30 points)
•Pick the address of a site you visit.
You are going to use it to test some
network diagnostics. What happened
when you ping your site?
•Try it with a few more examples.
What is happening?
•How can ping be useful?
Type ping /? To find the various
options there are
Using the count request option to
send 5 instead of 4
Useful or not?
• Simply pinging a remote host (a computer
that is on one’s internet but not on one’s
network) usually has an all or nothing
outcome and as such can provide somewhat
limited information
• A sequence of pinging can provide more
information (see MCSE TCP/IP for
Dummies)
Pinging yourself using localhost or
127.0.0.1: verifies that TCP/IP has
been installed and started correctly
Reserved IP address
Pinging yourself using your IP,
checks that the IP is valid
You can use another utility
ipconfig to find your IP if you
don’t know it
Go to the start command
Select the option run and type
command.com
You now have the black window and we are
going to use this to check our connection.
Run ipconfig—what is your address? What
can you tell from your about your
connection?
Pinging the Gateway – timing out
here may indicate a problem with
the router
Gateway
• Recall that one gets an internet by
connecting more networks
• The point at which data leaves one
(local) network and enters another is
known as a gateway
• A node (a device on the Internet) can be
either a gateway, router, or a host (endpoint).
Host/Gateway
• When you are looking at some site on
the net, your computer and the one
containing the site are hosts
• On the other hand, the computers that
direct the traffic, for example your
Internet service provider (ISP) are
gateway/router nodes.
Traceroute
• A utility that traces (determines the route taken by)
a packet from your computer (the local host) to
some other host on the network
– It doesn’t actually follow a single packet but sends out a
series of packets
– The packets are restricted in the number of “hops” they
can take
• It is limited by the time-to-live (TTL) field
– When the limit is reached, information about the node
is (should be) returned
– Each consecutive packet is allowed one more hop
hop
• A hop is when a packet is transmitted from
one node to the next.
• “Some Internet Service Providers (ISPs)
advertise how many hops away from
Internet backbone they are. Theoretically,
the fewer hops it takes to get your data onto
the backbone, the faster your access will
be.” (webopedia)
Traceroute (Cont.)
• Traceroute shows how many hops were
required to reach the destination as well as
the length of time for each hop.
• When the web is sluggish, you can use
traceroute to determine where the
congestion lies.
Traceroute (Cont.)
• The original traceroute was for UNIX utility
• Windows has a traceroute utility called
tracert.
• Go to Start/Run, type cmd, and then type
“tracert” followed by the domain name of
the host.
• For example:
tracert www.webopedia.com
tracert www.whatis.com
Tracert Exercise Part 2 (40 points)
• Using the command.com and tracert
command, find the command to
• www.whatis.com
• 139.84.19.200
• Ask your neighbor for their ip address—
trace the route to them.
Other TCP/IP diagnostic
commands
•
•
•
•
•
•
•
Nbtstat
Netstat
Ipconfig
Arp
Hostname
Route
Look up these commands and see what they mean.
Prepare a table with the list and the job of each
command….site your sources.
Another Exercise part 3 (30 points)
• Find the ipconfig for your machine.
• Open the command window
• Look at the options for the NBTSTAT
command.
• Run the NBTSTAT command using your ip
address for your machine. Use the –A
option. What did you find out?
Other sources
• http://www.webopedia.com
• http://www.whatis.com