N$5\mathrm{.}2.$ If an application needs to ensure the order of the packets, but UDP does not provide such a guarantee, does the

application have to use TCP$?$ Can it still use UDP?

N$5\mathrm{.}3.$ Why is UDP in general more suitable for real$-$time applications than TCP$?$

N$5\mathrm{.}4.$ In the following code snippet, what does the IP address $0\mathrm{.}0\mathrm{.}0\mathrm{.}0$ means?

udp $=$ socket.socket$(socket.A{F}_{\text{I}}$NET, socket.$SOC{K}_D$GRAM$)$

udp.bind$((0\mathrm{.}0\mathrm{.}0\mathrm{.}0,9090))$

N$5\mathrm{.}5.$ When spoofing a UDP packet using Scapy, why do we typically set the UDP checksum field to zero?

N$5\mathrm{.}7.$ An open$-$source program has the following behavior: after receiving a message on its

UDP port, it immediate sends a response to the client. Alice runs such a program on her

machine $(10\mathrm{.}8\mathrm{.}0\mathrm{.}8),$ using port $8000.$ Bob also runs the program on his machine

$(192\mathrm{.}168\mathrm{.}0\mathrm{.}7),$ using port $7000.(1)$ Please write a simple Python program to trigger a UDP

ping pong between these two machines. $(2)$ Please describe how you can help this open$-$source

program fix this problem $($just describing your solution would be sufficient$).$

N$5\mathrm{.}8.$ What type of services are good candidates for the UDP amplification attack?

N$6\mathrm{.}1.$ This problem is based on following TCP client program. $(1)$ To get responses from the server, the TCP client

program should register for a source port number, but in the program, this step seems to be missing. Without this port

number, how can the client program get responses? $(2)$ Which line of the code triggers the three$-$way handshake

protocol? $(3)$ There are two sendall $()$ calls in this client program, will each call trigger a separate TCP packet?

#$!/$bin$/$env python$3$

import socket

tcp $=$ socket.socket $($socket$.$AF$\_$INET, socket.SOCK$\_$STREAM$)$

tcp$.$connect $((\text{'}10\mathrm{.}0\mathrm{.}2\mathrm{.}69\text{'},9090))$

tcp$.$sendall $($b$"$Hello Server!

$")$

tcp$.$sendall $($b$"$Hello Again!

$")$

tcp$.$close $()$

N$6\mathrm{.}2.$ This problem is based on the following TCP server program. $(1)$ Does the program

get blocked when invoking listen$()$ until a connection comes? $(2)$ What is the

purpose of the accept $()?(3)$ Why does the accept $()$ call create a new socket?

Why cannot we use the same one that is used in the listen$()$ call?

#$!/$bin$/$env python$3$

import socket

tcp $=$ socket.socket $($socket$.$AF$\_$INET, socket.SOCK$\_$STREAM$)$

tcp$.$bind $(("0\mathrm{.}0\mathrm{.}0\mathrm{.}0",9090))$

tcp$.$listen$()$

print $($data$)$

conn. sendall $($b$"$Got the data!

$")$