CS 779/879
Design of Network Protocols
Spring 2013
Second Exam
Time 2 & 1/2 hours
Open Book

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All questions are of equal weights.

Question 1:

A. In assignment #4 you were asked to write a general chat client with the following options:

{ m, t, s, q, x, l}. Show which of these options can be easily implemented using the sock program. Explain?

B. Two users, one at something and the other at somethingmore, have decided to use the sock program to chat with each other as follows:

something % sock –s 10555

somethingmore % sock something 10555

What is the property of sock that enabled them to chat?

C. Assume that DrWahab was logging into something and he wanted to start a tcp server using his favorite port “10555” but he gets the error message: “Address already in use”

Describe how DrWahab can discover the login name of the person using port 10555 so that he can send that person a message to release the port in exchange of a better grade in his cs779/879 course J

D. In simultaneous open, how may handshake TCP packets are exchanged to establish a tcp connection

between the two client programs?

E. In simultaneous close, how many handshake TCP packets are exchanged to close a tcp connection?

Question 2:

A. List all possible types of server sockets that can simultaneous use the same port number (e.g., 10555)

on the same host without getting the error message: “Address already in use”.

B. Give an example of a situation where we must use recv on a TCP socket.

C. Give an example of a situation where we must use recvmsg on a UDP socket.

Question 3:

A possible server design alternative is to combine pre-forking & forking-on-demand as follows:

· The main process creates a server socket S and forks N children processes.

· The N processes accept connections at S and one by one serve the incoming clients.

· If a client arrives while all the N children processes are busy serving clients,

the main process steps forward and accepts that client and creates a temporary child

to serve that client. The temporary child process exits upon serving the client.

Explain how the main process can monitor the N children and S to implement this combined approach?.

Question 4:

Implement the following program:

portscan <host>

The program connects to every tcp ports at <host> and prints out those ports it successfully connects to.

Your implementation should be very fast by not waiting for the default long time it may rake for the connect call to return; sometimes it can be time 2 minutes.

Question 5:

A. Consider the following set of SCTP Servers and Clients programs:

Each program is named: XYZ, where:

X {S: Server, C: Client}

Y {4: IP4, 6: IP6}

Z {S: Stream, Q: Sequence Packet}

S4S: Server IPv4 Stream

S6S: Server IPv6 Stream

C4S: Client IPv4 Stream

C6S: Client IPv6 Stream

S4Q: Server IPv4 Sequence Packet

S6Q: Server IPv6 Sequence Packet

C4Q: Client IPv4 Sequence Packet

C6Q: Client IPv6 Sequence Packet

Each client has to specify the IP address of the server. The IP address of the server may be specified using one or more of the following three format:

4: IPv4 address format, e.g: 128.82.4.210

6: IPv6 address format, e.g: fe80::203:baff:fe2a:67ff

f: IPv4-mapped IPv6 address, e.g., ::ffff:128.82.4.210

Use the above symbols i {4, 6, f} to fill in each entry in the following Table with all possible correct address formats that can be used by a client to interact with the corresponding server:

	C4S	C6S	C4Q	C6Q
S4S
S6S
S4Q
S6Q

B. Consider the following set of TCP/UDP Servers and Clients programs:

Program Name: XYZ, where:

X {S: Server, C: Client}

Y {4: IP4, 6: IP6}

Z {T: TCP, U: Unicast, M:Multicast}

S4T: Server IPv4 TCP

S6T: Server IPv6 TCP

S4U: Server IPv4 UDP

S6U: Server IPv6 UDP

S4M: Server IPv4 Multicast

S6M: Server IPv6 Multicast

ü The UDP Servers receives unicast messages and send unicast replies to senders

ü The Multicast Server receives unicast & multicast messages and sends unicast replies to senders

C4T: Client IPv4 TCP

C6T: Client IPv6 TCP

C4U: Client IPv4 UDP

C6U: Client IPv6 UDP

C4M: Client IPv4 Multicast

C6M: Client IPv6 Multicast

Each of these clients concurrently:

· Reads messages from 0 and send it to socket

· Reads messages from socket send send it 1.

ü The UDP Clients send and receives unicast messages.

ü The Multicast Clients send multicast messages and receives unicast & multicast messages.

The IP address may be specified using one or more of the following three formats:

4: IPv4 address format, e.g: unicast 128.82.4.210 & multicast 224.0.0.1

6: IPv6 address format, e.g unicast fe80::203:baff:fe2a:67ff & multicast ff80::203:baff:fe2a:6722

f: IPv4-mapped IPv6 address, e.g., unicast ::ffff:128.82.4.210 & multicast ::ffff:224.0.0.1

Use the above symbols (4, 6, f) to fill in each entry in the following Table with all possible correct address formats that can be used by a client to interact with the corresponding server:

	C4T	C6T	C4U	C6U	C4M	C6M
S4T
S6T
S4U
S6U
S4M
S6M