Ping and traceroute

Lab/Homework exercise Assigned 9/12/2006

Due 9/19/2006CSIT 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

Can use IP instead of domain name

Timed out

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 commandSelect the option run and type command.comYou 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 (end-point).

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