Chapter 9

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Copyright © 2011 Pearson Education, Inc. Publishing as Prentice
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HOMEWORK

CHAPTER
9

TCP/IP Internetworking

Last Name: _____________________________

First Name: _____________________________

DIRECTIONS:

To answer a question, place your cursor at the end of the question and hit Enter.

This will put you into the Answer sty
le, which is indented.

If that doesn’t work, click in an answer paragraph and type
Alt
-
Control
-
A.

TEST YOUR UNDERSTAND
ING

QUESTIONS

1.

a) Compare TCP

and IP al ong the di mensi ons i n Fi gure 9
-
2.


b) Compare TCP and UDP al ong the di mensi ons i n Fi gure 9
-
2.

2.

a) What i s
routi ng?

b
) What are the three parts of an IP address?

c) How long is each part
?

d) What i s the total l ength of an IP address?


e)

In the IP address, 10.11.13.13, what is the network part
?

3.

a) Connecti ng di fferent networks i s the mai n job of w
hat type of router?

b) What type of router onl y connects di fferent subnets?

4
.

a) How many bits are there in a mask
?

b)

What do the 1s i n a network mask correspond to i n IP addresses?

c)

What do the 1s in a subnet mask correspond to in IP addresses
?

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d)

Whe
n a network mask is applied to any IP address on the network, what is the result
?

5
.

a) Li st the bi ts
(1s and 0s)
i n the mask

255.255.255.0.

b) What are the bits (1s and 0s) in the mask /14
?

c) If /14 i s the network mask, how many bi ts are there i n the net
work part?

d) If /14 i s the network mask, how many bi ts are there i n the subnet part?

e) If /14 i s the network mask, how many bi ts are there i n the host part?

f) If /14 is the subnet mask, how many bits are there in the network part
?

g) If /14 is the subne
t mask, how many bits are there in the subnet part
?

h)
If /14 is the subnet mask, how many bits are there in the host part
?

6
.

Why are routing tables more complex than Ethernet switching tables? Be articulate
.

7
.

a)

In a routing table, what does a row repr
esent
?

b)

Do switches have a row for each individual Ethernet address
?

c)

Do routers have a row for each individual IP address
?

d)

What is the advantage of the answer to the previous subpart of this question
?

8
.

a)

In Row 3 of Figure 9
-
8, how will a router

test if the row matches the IP address 60.168.6.7? Show the
calculations. Is the row a match
?

b)

Why is the last row called the default row
?

c)

Why must a router look at all rows in a routing table
?

d)

What rows match 172.30.17.6
?

e)

Which rows match 60.1
68.7.32? Show your calculations for rows that match
.


f)

Which rows in Figure 9
-
8 match 128.171.17.13? (Don’t forget the default row.) Show your calculations
for rows that match
.

9.

a)

Distinguish between Step 1 and Step 2 in the routing process
.

b)

If any

row other than the default row matches an IP address, why will the router never choose the
default row
?

c)

Which rows in Figure 9
-
8 match 128.171.17.13? (Don’t forget the default row.) Show your
calculations
.

d)

Which of these is the best
-
match row? Justi
fy your answer
.

e)

What rows match 172.40.17.6
?

f)

Which of these is the best
-
match row? Justify your answer
.

g)

Which rows match 172.30.12.47? Show your work
.

h)

Which of these is the best
-
match row? Justify your answer
.


i)

How would your previous answer

change if the metric had been reliability
?

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10
.

a)

Distinguish between Step 2 and Step 3 in routing
.

b)

What are router ports called
?

c)

If the router selects Row 13 as the best match row, what interface will the router send the interface
out
?

d)

To what d
evice
?

e)

Why is this router called the default router? (The answer is not in the text
.)

f
)

If the router selects Row

2 as the best
-
match row for packet 172.30.33.6, what interface will the
router send the interface out
?

g)

To what device? (Don’t say, “the

local device
.”)

11.

a)

What should a router do if it receives several packets going to the same destination IP address
?

b)

How woul d deci si on caching speed the routi ng deci si on for packets after the fi rst one?

c)

Why i s deci si on caching dangerous?

12
.

a)

An arriving packet has the destination IP address 128.171.180.13. Row 86 has the destination value
128.171.160.0. The mask is 255.255.224.0. Does this row match the destination IP address? Show your
work. You can use Windows Calculator if you have a Window
s PC. In Windows Vista and earlier versions
of Windows, choose scientific when you open the calculator. In the Windows 7 calculator, choose
programmer mode
.

13
.

A router wi shes to send

an IP packet to a host on i ts subnet. It knows the host’s IP address.

a
) What el se
must i t know?

b) Why must it know it
?

c) What message wi l l i t broadcast?

d) What devi ce wi l l respond to thi s broadcast message?

e) Does a router have to go through the ARP process each time it needs to send a packet to a
destination host or to
a next
-
hop router? Explain
.

f) Is ARP used to find the destination data link layer destination addresses of destination hosts, routers,
or both
?

g) At what l ayer does the ARP protocol operate?

h
)
Why must cl i ent PCs use ARP to transmi t packets? The answer
i s not i n the text.

14
.

a)

What i s the mai n versi on of the Internet Protocol i n

use today?

b)
What does a router do if it receives a packet with a TTL value of 1
?

c)
What does the protocol fi el d val ue tel l the desti nati on host?

d)
Under what ci rcumstances

woul d the i denti fi cati on, fl ags, and fragment offset fi el ds be used i n IP?

e)
Why i s IP fragmentati on suspi ci ous?

f)
Why are IP opti ons suspi cious?

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g) What i s the purpose of the Di ff
-
Serv fi el d?

15
.

a)

How is IPv6 better than IPv4
?

b)

Why
has IPv6 adopti
on been so sl ow?

c)

What forces may drive IPv6’s adoption in the future
?

d)

Must

IPv6 repl ace IPv4 al l at once? Expl ai n.

16
.

a) Why i s TCP compl ex
?

b)
Why i s i t i mportant for networki ng professi onal s to understand TCP?

c)
What are TCP messages called
?

17
.

a) Why are sequence numbers good
?

b)
What are 1
-
bi t fi el ds cal led?

c)
f someone says that a flag field is set, what does this mean
?

d)
f the ACK bi t i s set, what other fi el d must have a val ue?

e)
What is a FIN segment
?

f) Distinguish between four
-
way c
loses and abrupt resets
.


g)

Why is a reset segment not acknowledged
?

18
.

a) What type of port number do servers use?


b)

What type of port number do cl i ents use?


c)

What is the port range for well
-
known port numbers
?


d)

What is the range of Microsoft ep
hemeral port numbers
?

19
.

A Windows host sends a TCP segment with source port number 25 and destination port number 2404.
a)
Is the source host a server or a client? Explain
.


b)

If the host is a server, what kind of server is it
?

c)

Is the destination h
ost a server or a client? Explain
.

20.

a) What is a socket
?

b)

What specifies a particular application on a particular host in TCP/IP
?

c)

How is it written
?

d)

When the SMTP server in Figure 9
-
13 transmits to the client PC, what will the source socket be
?

e)

The destination socket
?

21
.

a) What i s the purpose of dynami c

routi ng protocol s?

b) In what two ways does TCP/IP use the term
routing
?

22
.

a) What i s an autonomous

system?

b)

Wi thi n an autonomous system, can the organi zati on choose i ts i nteri or routi ng
protocol?

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Copyright © 2011 Pearson Education, Inc. Publishing as Prentice
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c) What are the two TCP/IP interior dynamic routing protocols
?

d) Whi ch IETF dynami c routi ng protocol i s good for smal l i nternets that do not have hi gh securi ty
requi rements?

e) Whi ch IETF dynami c routi ng protocol i s good for l arge i nternal i nter
nets that have hi gh securi ty
requi rements?

f) What i s the mai n benefi t of EIGRP compared to OSPF as an i nternal dynami c routi ng protocol?

g) When might you use EIGRP as your interior dynamic routing protocol
?

h) May a company sel ect the routi ng protocol i t
s border router uses to communi cate wi th the outsi de
worl d?

i )

What i s the al most uni versal exteri or dynami c routi ng protocol?

23
.

a)

For what general class of messages is ICMP used
?

b
)

Expl ai n error advi sement

i n ICMP.

c
)

Expl ai n the purpose

of ICMP echo
messages.

d)

Sending an ICMP echo message is called __________ the target host
.

24
.

a) In MPLS, is selecting the best interface for each packet done when the packet arrives or before the
packet arrives
?


b)

What is the name of the path selected for a parti
cular conversation
?


c)

When a source host first transmits to a destination host, what will happen
?


d)

Do label
-
switching routers along the MPLS path look at the packet’s IP address? Explain your
reasoning
.


e)

Why is MPLS decision making fast compared to

traditional routing
?


f)

On what does each label
-
switched router base routing decisions
?


g)

Why is MPLS transparent to the source and destination hosts
?


h) What i s MPLS’s mai n attracti on?


i )

What are i ts other attracti ons?


j)

What i s traffi c engi neeri
ng?


k) Can MPLS provi de traffi c l oad bal ancing?


l)

Why is it impossible to implement MPLS on the entire Internet
?

END
-
OF
-
CHAPTER QUESTIONS

Thought Questions

1.

How does the postal service use hierarchical sorting? How does this simplify delivery
decision
s?

2
.

Gi ve a non
-
network exampl e of hi erarchi cal addressing, and di scuss how i t reduces the amount of work
needed i n physi cal del i very. Do not use any exampl e i n the book, the postal servi ce, or the tel ephone
network.

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3
.

A cl i ent PC has two si mul taneous co
nnecti ons to the same webserver appl i cati on program on a
webserver. (Yes, thi s i s possi ble, and i n fact
,

i t i s rather common.) What wi l l be di fferent between the TCP
segments that the cl i ent sends on the two connecti ons?

4.

A router that has the routi ng ta
bl e i n Fi gure 9
-
8 recei ves an i ncomi ng packet. The source IP address i s
10.55.72.234. The desti nati on host i s 10.4.6.7. The TTL val ue i s 1. The Protocol fi el d val ue i s 6. What wi l l
the router do wi th thi s packet?

Harder Thought Questions

1
.

For securi ty re
asons, many organi zati ons do not al l ow error repl y messages to l eave thei r i nternal
i nternets. How, speci fi cal ly, coul d hackers use i nformati on i n echo repl y messages to l earn about the
fi rm’s i nternal hosts?

Troubleshooting Question

1.

You suspect that

th
e fai l ure of a router or of a transmi ssion l i ne connecti ng routers has l eft some of your
i mportant servers unavai l able to cl i ents at your si te. How coul d you narrow down the l ocati on of the
probl em usi ng what you l earned i n thi s chapter?

Perspective Questi
ons

1
.

What was the most surpri sing thi ng you l earned i n thi s chapter?

2
.

What was the most

di ffi cul t materi al for you i n thi s chapter?