Answer to Question #244440 in Computer Networks for Ahsan wains

Question

UDP

Open the “udp_packet_capture” trace file and select the first DNS query packet from the trace. Hint: To limit yourself to DNS packets, enter the string DNS in the filter field and then apply the filter.

a. By consulting the displayed information in Wireshark’s packet content field for this packet, determine the length in bytes of each of the UDP header fields.

b. By examining the UDP header explain whether or not UDP can provide reliability.

c. What is the maximum number of bytes that can be included in a UDP payload?

d. What is the protocol number (in hex) for UDP?

e. What is the source port number for the query?

f. What is the destination port number for the response? 

Answer 1

a) From the given data packets, we can identify the UDP packet -

Length is : 1345

b)

UDP provides the unreliable server. UDP protocol does not support the reassembly of fragmented data-grams. UDP data-gram payloads are very limited in general. Payloads above 512bytes are fragmented by routers so effectively lost.

c) Maximum number of byte that can be included in UDP payload $(2^{16}-1)$ +header bytes=65527-8=65527 bytes

d)

The IP protocol number for UDP is 0x11 hex, which is 17 in decimal value.

e)

From the attached diagram we can see that the source port is 61209.

f)Destination port : 443