Department of Computer Science and Engineering
Southern Methodist University
Dallas, Texas 75205
Internetworking Protocols
and Programming
CSE 5348/7348
Fall 2004
This is a closed book, closed-notes
exam. You may use a cheat sheet not
bigger than 8.5”x11”. This exam
should be completed in an hour and a
half
Name:_________________
Grade:__________________
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Department of Computer Science and Engineering
Southern Methodist University
Dallas, Texas 75205
Midterm Examination
CSE 5348/7348
Fall 2004
Name: ________________________________
Student ID: ________________________________
1. Choose the most appropriate answer to the
following questions by circling the letter
corresponding to your choice. You may choose
only one of the options.
1. The Algorithm used by CSMA/CD for collision avoidance is
a. Random Early Detection
b. Binary Exponential Back-off
c. Message Tossing
d. IP shedding
2. 100 BaseT involves data transmission at
a. rates of 1 Gigabits/sec over multimode fiber
b. a rate faster than 155 Kbps
c. a rate that is 1002 Kbps
d. 100 Mbps using unshielded Twisted pair
3. Changing the Ethernet card on an interface means that
a. the interface IP address will change
b. all hubs will have to be reconfigured
c. the routers will have to be reconfigured
d. the interface MAC address will change
4. The address 0.0.0.0 indicates
a. a host that does not exist on the network
b. the logical local loopback device
c. all hosts on the network
d. “this” host
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Department of Computer Science and Engineering
Southern Methodist University
Dallas, Texas 75205
5. The Address Resolution Protocol
a. is used for acquiring the IP address of a machine given
its MAC address
b. is a Layer three networking protocol
c. is used to find the MAC address of a machine given its
IP address
d. is used for acquiring the IP address of a machine given
its domain name
6. Well Known Ports (WKP) are those in the range
a. 0-1023
b. 3000-65535
c. 4096-65535
d. 1024-2014
7. The Reverse Address Resolution Protocol
a. is used for mapping ATM identifiers to an IP address
b. is used to find the IP address of a machine given its
MAC address
c. requires the deployment of ARP Servers on the physical
network
d. has been replaced by such protocols as DNS and SNMP
8. The destination IP address of a packet moving from a private
address space to a public address space through a NAT
a. is mapped to a public address by the NAT
b. is left untouched by the NAT
c. is mapped to its own address by the NAT
d. none of the above
9. The true statement is
a. The world will run out of IP addresses soon since IP
addresses are a lot shorter than MAC addresses
b. IP version 6 was introduced primarily to allow more
unique domain names to be deployed globally
c. A Network interface card by default picks up only
Ethernet frames whose destination MAC address
matches its own
d. A network address translator acts as a Transparent
Router
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Department of Computer Science and Engineering
Southern Methodist University
Dallas, Texas 75205
10. The Internet Protocol uses the “DF” flag in a datagram to
indicate that
a. a packet should not be fragmented by intermediate
routers
b. the packet should be direct-forwarded
c. the packet is delay sensitive
d. the sender should be notified if the destination address
fails to exist
11. The Checksum field in the IP header
a. applies only to the data in the packet
b. applies to both header and data
c. applies to only the IP header and not to data
d. is recomputed by all routers over the entire IP datagram
12. The User Datagram Protocol is
a. used by Layer 5 protocols such as FTP
b. connection oriented but not reliable
c. a connectionless, unreliable protocol
d. a connectionless protocol that is reliable
13. The checksum field in the UDP header
a. applies only to the UDP data in the packet and not to
the header
b. is mandatory by IETF standards
c. is never used
d. applies to the entire UDP datagram
14. Port numbers in the UDP header of a datagram
a. uniquely identify the end-point machines
b. uniquely identify the end-point applications
c. identify the end-point machines and the applications
involved in the UDP transaction
d. can never be the same
15. The ICMP protocol
a. is a Layer 2 protocol co-existing with ARP/RARP
b. is used only for error detection and correction
c. has no associated port numbers and is therefore a Layer
3 protocol
d. is encapsulated in IP and is therefore a Layer 4 protocol
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Department of Computer Science and Engineering
Southern Methodist University
Dallas, Texas 75205
16. A UDP client
a. can talk only to a UDP server
b. can talk either to a UDP server or a TCP server
c. cannot invoke the connect function call
d. should never be several hops away from the server due
to the lack of a mandatory checksum field
17. The local loopback device
a. supports only ICMP sockets
b. cannot be used for inter-process communications on the
same machine
c. is always assigned the address 127.0.0.1
d. supports only UDP sockets
18. A Class D IP address
a. should never be seen in the destination field of an IP
datagram on the network
b. is reserved for use by routers alone
c. is an experimental block of IP addresses
d. is used for multicasting packets to several hosts
19. Raw sockets are
a. sockets that haven’t yet been bound to an IP address
b. standardized and portable across a variety of platforms
c. malicious and should never be used on the internet
d. sockets that allow you to construct ICMP packets
20. When the TTL field of the IP header in a packet becomes zero,
the router handling the packet
a. bounces the packet back to the sender
b. drops the packet and generates an ICMP “TTL expired
in transit” message to the intended receiver
c. silently drops the packet
d. drops the packet and generates an ICMP “TTL expired
in transit” message to the sender
_________________________________________________________
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Department of Computer Science and Engineering
Southern Methodist University
Dallas, Texas 75205
2. Reasoning Exercises
You will be given credit for using proper
terminology and for being concise. Give your
answer in the space provided.
1. A dual-homed host machine has two Ethernet interfaces
connected to the same physical network. One is assigned the IP
address 129.0.0.4 and the other 129.0.0.5. A UDP server
application offers database services at address 129.0.0.4 port
3305. A client application running on port 3010 of 129.0.0.5
requests services by sending a request message to the server.
The request datagram is 900 bytes long and is carried in a UDP
packet. Frames on the LAN can be observed with the help of a
Sniffer.
a. Assuming the Ethernet MTU is set to 512 bytes, how
many frames will be seen on the Ethernet LAN during
the exchange?
b. How many frames would you observe on the LAN if
the “Don’t Fragment” Flag were set in the IP datagram
that the client sends?
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Department of Computer Science and Engineering
Southern Methodist University
Dallas, Texas 75205
2. A Physical network has a network ID of 47.104.56.0 and a
subnet mask of 255.255.248.0 written as 47.104.56.0/21. The
network consists of three machines A, B, C and a gateway R
(default router). The static IP address assignments and default
router configuration for the network is as shown in the table
below. The person who configured machine C erroneously set
its subnet mask to 255.255.255.0, or a prefix of 24 instead of
21. All other parameters are properly and statically assigned.
Machine
Router
A
B
C
IP address
47.104.56.1
47.104.56.3
47.104.59.115
47.104.59.117
Subnet mask
255.255.248.0
255.255.248.0
255.255.248.0
255.255.248.0
Assigned mask
255.255.248.0
255.255.248.0
255.255.248.0
255.255.255.0
Indicate what happens for each of the following use cases.
Explain the request/response messaging in each case:
a. Host A sends out ARP request for Host B.
b. Host C sends out ARP request for Host B
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Department of Computer Science and Engineering
Southern Methodist University
Dallas, Texas 75205
c. Host B sends an ICMP echo request to Host C
d. Host A sends an ICMP echo request to Host C
3. The traceroute application was run on a machine named
“Cycloid” [192.168.0.7/24] to get the following output. Answer
the following questions based on the screen shot:
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Department of Computer Science and Engineering
Southern Methodist University
Dallas, Texas 75205
a. How many routers exist between the machines Cycloid
and Rapid? Does this correspond to the shortest
geographical distance between Cycloid and Rapid?
b. Do you notice any private networks with non-routable
IP addresses being traversed? If so, what functional
device might have been used to implement this?
4. The Record Route Option in an IP datagram holds a length
field and a pointer field. A router forwarding a packet with this
option inspects the pointer field and the length field in the IP
optional header.
8
0
Code (7)
24
16
Length
31
Pointer
First IP address
Second IP address
...
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Department of Computer Science and Engineering
Southern Methodist University
Dallas, Texas 75205
Answer the following questions:
a. Explain router action if the length field holds the
number 0000 10112 and the pointer field holds the
number 0000 01002.
b. Explain router action if the length field holds the
number 0000 10112 and the pointer field holds the
number 0000 11002
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Department of Computer Science and Engineering
Southern Methodist University
Dallas, Texas 75205
3. Design Problems
You will be given credit for using proper terminology
and for being concise. Give your answer in the space
provided.
1. A router has learned of all reachable networks from neighboring routers.
The list of networks is shown in the table below:
Classless
Addresses
53.0.0.0
70.0.0.0
86.0.0.0
97.0.0.0
170.240.0.0
Identify the unique prefixes and construct a binary trie for the above
information.
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Department of Computer Science and Engineering
Southern Methodist University
Dallas, Texas 75205
2. An address block 47.104.56.0/21 is made available to you for
deployment. The network you have to implement consists of
three subnets interconnected by two routers. Each subnet will
hold no more than 254 host machines. Fill in the blanks in the
topology diagram. Supply IP addresses for all Router
Interfaces. Identify each cloud with its Network ID and subnet
mask. Fill in the information for the Client and Server
machines. You are free to choose addresses as long as they fall
within the allocated block.
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