N$1\mathrm{.}1.$ What is the network prefix for each of the following hosts: $(1)10\mathrm{.}1\mathrm{.}2\mathrm{.}200/24$ and

$(2)10\mathrm{.}1.\frac{2\mathrm{.}200}{26}?$

N$1\mathrm{.}3.$ We write the following program to send a packet. $(1)$ How is the source port number of

the packet decided? $(2)$ How is the source IP of the packet decided?

data $=$ b$"$Hello$,$ Server $\frac{?}{?}$

udp $=$ socket.socket $($socket$.$AF$\_$INET, socket.sOCK$\_$DGRAM$)$

udp.sendto $($data$,("10\mathrm{.}9\mathrm{.}0\mathrm{.}5",-9090))$

N$1\mathrm{.}4.$ When we construct a packet, we need to set the address at each layer. What are the

addresses called at he following layers: $(1)$ transport layer, $(2)$ network layer, and $(3)$

data link layer?

N$1\mathrm{.}5.$ When we run $"$nc $-$lnu $9090",$ what does the options "lnu" mean?

N$1\mathrm{.}6.$ What does the bind do in the following code snippet? What is the meaning of

$0\mathrm{.}0\mathrm{.}0\mathrm{.}0?$

If we are only interested in the packets coming from the localhost, what should be do$?$

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$1\mathrm{.}7.$ In a server program, we bind the program to a port number, so when a packet comes to

that port, the OS knows which program is the recipient of the packet. However, for the

client program, we typically do not do the binding. When a reply from the server

comes, how does the OS know that this client program is the recipient?

N$1\mathrm{.}8.$ Why does the sniffing use the superuser privilege?

N$1\mathrm{.}9.(1)$ Write down the tcpdump command to print out all the packets to UDP destination

port $53$ on the interface xyz$.(2)$ Write down the tcpdump command to print out all

the packets from port $1000$ to port $53$ on the interface $xyz.$

N$1\mathrm{.}10.$ Please explain the purpose of each of the arguments in the following Scapy code snippet.

$pkt=$ sniff$(iface=\text{'}$ etho', filter$=$'icmp', $prn=prin{t}_{p}kt)$

N$1\mathrm{.}11.$ The following result of the $"$ip address" command shows all the network inter$-$

faces on a host. Please write a Scapy program to sniff the packets transmitted over the

$192\mathrm{.}168\mathrm{.}5\mathrm{.}0/24$ network. You are only interested in the UDP packets to $8\mathrm{.}8\mathrm{.}8\mathrm{.}8\text{'}$s

port $53.$