computer network(Wireshark ) due after 12 hours

Lab Assignments for Chapter 3

We have created two lab assignments for this chapter: Lab3-1 and Lab3-2. We have

also included two lab-report sheets, which means that each assignment should be

reported in a separate sheet.

Lab3-1: UDP

In this lab, we use Wireshark to capture and study UDP packets. We find the values of

different fields of a UDP user datagram header. Using the values in these fields, we also

find all the information about a user datagram and verify that the value in total length

field matches with the total number of bytes in the user datagram (header and data). We

also check to see whether a checksum has been calculated for the packet.

UDP is a connectionless protocol; no connection-establishment and connectiontermination

packets are issued by UDP. This means that UDP cannot be a source or

sink protocol in a captured frame. To analyze UDP headers, we need to use a source or

sink protocol at the application layer that uses the services of UDP. DNS is a good candidate.

However, as we learned in Chapter 2, DNS packets can be encapsulated in

either UDP or TCP packets (depending on the size). We need to be careful to select

only those DNS packets that use the service of UDP.

Since any client-server application program (except DNS itself) uses DNS as the

first step, we can open any application to capture DNS packets. We recommend to

access your favorite website for this purpose.

Assignment

■ Start your web browser and clear the browser's cache memory, but do not access

any website yet.

■ Open Wireshark and start capturing.

■ Go back to your web browser and retrieve any file from a website. Wireshark

starts capturing packets.

■ After enough packets have been captured, stop Wireshark and save the captured

file.

■ Using the captured file, select only those DNS packets that use the service of UDP.

Type udp (lowercase) in the filter field and click Apply. The packet list pane of the

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Wireshark window should now display a bunch of DNS messages. Each DNS message

is carried in a UDP packet.