Chapter 19: Logical Addressing

19.1
Chapter 19
Network Layer:
Logical Addressing
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

19.2
19-1 IPv4 ADDRESSES19-1 IPv4 ADDRESSES
AnAn IPv4 addressIPv4 address is ais a 32-bit32-bit address that uniquely andaddress that uniquely and
universally defines the connection of a device (foruniversally defines the connection of a device (for
example, a computer or a router) to the Internet.example, a computer or a router) to the Internet.
Address Space
Notations
Classful Addressing
Classless Addressing
Network Address Translation (NAT)
Topics discussed in this section:Topics discussed in this section:

19.3
An IPv4 address is 32 bits long.
Note

19.4
The IPv4 addresses are unique
and universal.
Note

19.5
The address space of IPv4 is
232
or 4,294,967,296.
Note

19.6
Figure 19.1 Dotted-decimal notation and binary notation for an IPv4 address

19.7
Numbering systems are reviewed in
Appendix B.
Note

19.8
Change the following IPv4 addresses from binary
notation to dotted-decimal notation.
Example 19.1
Solution
We replace each group of 8 bits with its equivalent
decimal number (see Appendix B) and add dots for
separation.

19.9
Change the following IPv4 addresses from dotted-decimal
notation to binary notation.
Example 19.2
Solution
We replace each decimal number with its binary
equivalent (see Appendix B).

19.10
Find the error, if any, in the following IPv4 addresses.
Example 19.3
Solution
a. There must be no leading zero (045).
b. There can be no more than four numbers.
c. Each number needs to be less than or equal to 255.
d. A mixture of binary notation and dotted-decimal
notation is not allowed.

19.11
In classful addressing, the address
space is divided into five classes:
A, B, C, D, and E.
Note

19.12
Figure 19.2 Finding the classes in binary and dotted-decimal notation

19.13
Find the class of each address.
a. 00000001 00001011 00001011 11101111
b. 11000001 10000011 00011011 11111111
c. 14.23.120.8
d. 252.5.15.111
Example 19.4
Solution
a. The first bit is 0. This is a class A address.
b. The first 2 bits are 1; the third bit is 0. This is a class C
address.
c. The first byte is 14; the class is A.
d. The first byte is 252; the class is E.

19.14
Table 19.1 Number of blocks and block size in classful IPv4 addressing

19.15
In classful addressing, a large part of
the available addresses were wasted.
Note

19.16
Table 19.2 Default masks for classful addressing

19.17
Classful addressing, which is almost
obsolete, is replaced with classless
addressing.
Note

19.18
Figure 19.3 shows a block of addresses, in both binary
and dotted-decimal notation, granted to a small business
that needs 16 addresses.
We can see that the restrictions are applied to this block.
The addresses are contiguous. The number of addresses
is a power of 2 (16 = 24
), and the first address is divisible
by 16. The first address, when converted to a decimal
number, is 3,440,387,360, which when divided by 16
results in 215,024,210.
Example 19.5

19.19
Figure 19.3 A block of 16 addresses granted to a small organization

19.20
In IPv4 addressing, a block of
addresses can be defined as
x.y.z.t /n
in which x.y.z.t defines one of the
addresses and the /n defines the mask.
Note

19.21
The first address in the block can be
found by setting the rightmost
32 − n bits to 0s.
Note

19.22
A block of addresses is granted to a small organization.
We know that one of the addresses is 205.16.37.39/28.
What is the first address in the block?
Solution
The binary representation of the given address is
11001101 00010000 00100101 00100111
If we set 32−28 rightmost bits to 0, we get
11001101 00010000 00100101 0010000
or
205.16.37.32.
This is actually the block shown in Figure 19.3.
Example 19.6

19.23
The last address in the block can be
found by setting the rightmost
32 − n bits to 1s.
Note

19.24
Find the last address for the block in Example 19.6.
Solution
The binary representation of the given address is
11001101 00010000 00100101 00100111
If we set 32 − 28 rightmost bits to 1, we get
11001101 00010000 00100101 00101111
or
205.16.37.47
This is actually the block shown in Figure 19.3.
Example 19.7

19.25
The number of addresses in the block
can be found by using the formula
232−n
.
Note

19.26
Find the number of addresses in Example 19.6.
Example 19.8
Solution
The value of n is 28, which means that number
of addresses is 2 32−28
or 16.

19.27
Another way to find the first address, the last address, and
the number of addresses is to represent the mask as a 32-
bit binary (or 8-digit hexadecimal) number. This is
particularly useful when we are writing a program to find
these pieces of information. In Example 19.5 the /28 can
be represented as
11111111 11111111 11111111 11110000
(twenty-eight 1s and four 0s).
Find
a. The first address
b. The last address
c. The number of addresses.
Example 19.9

19.28
Solution
a. The first address can be found by ANDing the given
addresses with the mask. ANDing here is done bit by
bit. The result of ANDing 2 bits is 1 if both bits are 1s;
the result is 0 otherwise.
Example 19.9 (continued)

19.29
b. The last address can be found by ORing the given
addresses with the complement of the mask. ORing
here is done bit by bit. The result of ORing 2 bits is 0 if
both bits are 0s; the result is 1 otherwise. The
complement of a number is found by changing each 1
to 0 and each 0 to 1.

19.30
c. The number of addresses can be found by
complementing the mask, interpreting it as a decimal
number, and adding 1 to it.

19.31
Figure 19.4 A network configuration for the block 205.16.37.32/28

19.32
The first address in a block is
normally not assigned to any device;
it is used as the network address that
represents the organization
to the rest of the world.
Note

19.33
Figure 19.5 Two levels of hierarchy in an IPv4 address

19.34
Figure 19.6 A frame in a character-oriented protocol

19.35
Each address in the block can be
considered as a two-level
hierarchical structure:
the leftmost n bits (prefix) define
the network;
the rightmost 32 − n bits define
the host.
Note

19.36
Figure 19.7 Configuration and addresses in a subnetted network

19.37
Figure 19.8 Three-level hierarchy in an IPv4 address

19.38
An ISP is granted a block of addresses starting with
190.100.0.0/16 (65,536 addresses). The ISP needs to
distribute these addresses to three groups of customers as
follows:
a. The first group has 64 customers; each needs 256
addresses.
b. The second group has 128 customers; each needs 128
addresses.
c. The third group has 128 customers; each needs 64
addresses.
Design the subblocks and find out how many addresses
are still available after these allocations.
Example 19.10

19.39
Solution
Figure 19.9 shows the situation.
Group 1
For this group, each customer needs 256 addresses. This
means that 8 (log2 256) bits are needed to define each
host. The prefix length is then 32 − 8 = 24. The addresses
are

19.40
Group 2
means that 7 (log2 128) bits are needed to define each
host. The prefix length is then 32 − 7 = 25. The addresses
are

19.41
Group 3
means that 6 (log264) bits are needed to each host. The
prefix length is then 32 − 6 = 26. The addresses are
Number of granted addresses to the ISP: 65,536
Number of allocated addresses by the ISP: 40,960
Number of available addresses: 24,576

19.42
Figure 19.9 An example of address allocation and distribution by an ISP

19.43
Table 19.3 Addresses for private networks

19.44
Figure 19.10 A NAT implementation

19.45
Figure 19.11 Addresses in a NAT

19.46
Figure 19.12 NAT address translation

19.47
Table 19.4 Five-column translation table

19.48
Figure 19.13 An ISP and NAT

19.49
19-2 IPv6 ADDRESSES19-2 IPv6 ADDRESSES
Despite all short-term solutions, address depletion isDespite all short-term solutions, address depletion is
still a long-term problem for the Internet. This andstill a long-term problem for the Internet. This and
other problems in the IP protocol itself have been theother problems in the IP protocol itself have been the
motivation for IPv6.motivation for IPv6.
Structure
Address Space
Topics discussed in this section:Topics discussed in this section:

19.50
An IPv6 address is 128 bits long.
Note

19.51
Figure 19.14 IPv6 address in binary and hexadecimal colon notation

19.52
Figure 19.15 Abbreviated IPv6 addresses

19.53
Expand the address 0:15::1:12:1213 to its original.
Example 19.11
Solution
We first need to align the left side of the double colon to
the left of the original pattern and the right side of the
double colon to the right of the original pattern to find
how many 0s we need to replace the double colon.
This means that the original address is.

19.54
Table 19.5 Type prefixes for IPv6 addresses

19.55
Table 19.5 Type prefixes for IPv6 addresses (continued)

19.56
Figure 19.16 Prefixes for provider-based unicast address

19.57
Figure 19.17 Multicast address in IPv6

19.58
Figure 19.18 Reserved addresses in IPv6

19.59
Figure 19.19 Local addresses in IPv6

Chapter 19: Logical Addressing

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Chapter 19: Logical Addressing