Transcript 21 - UTRGV Faculty Web

21-IP addressing
Dr. John P. Abraham
Professor
UTPA
Chapters 19, 20
• I have already covered these concepts
elsewhere.
Addressing
• Physical
• Logical
IP address
• 32 bits
– Hierarchy – prefix and suffix
– Prefix identifies the network – given by IANA
In classful addressing, the network address (the
first address in the block) is the one that is
assigned to the organization. The range of
addresses can automatically be inferred from the
network address.
– Suffix identifies the computer –given locally
– No two computers can have the same public IP
Octets
• IP address is written in 4 octets with
separating dots.
• 10000000.00001011.00000011.00011111
• 128.11.3.31
• One of the UTPA CS address is:
• 10000001.01110001.10000010.01101110
• What is this address in decimal notation?
Classful IP addressing
• Divided IP address space into three
primary classes A, B, C and also there
exist class D (multicasting) and E.
• First four (MSB) bits will determine its
class
Class
Lea
ding
Bits
Size of
Network
Number
Bit field
Size of
Rest
Bit
field
Number
of
Networks
Addresse
s
per
Network
Start
addres
s
End
address
Class A
0
8
24
128
(2 )
16,777,
24
216 (2 )
0.0.0.0
Class B
10
16
16
16,384
(2 )
65,536
(2 )
128.0.0. 191.255.
0
255.255
Class C
110
24
8
2,097,1
21
52 (2 )
Class D
(multicast)
1110
not
defined
not
defined
not
defined
not
defined
224.0.0. 239.255.
0
255.255
Class E
(reserved)
1111
not
defined
not
defined
not
defined
not
defined
240.0.0. 255.255.
0
255.255
7
14
16
8
256 (2 )
127.255.
255.255
192.0.0. 223.255.
0
255.255
Finding the address class
Figure 4.5
Finding the class in decimal notation
Find the class of each address:
a. 227.12.14.87
d. 252.5.15.111
b.193.14.56.22
e.134.11.78.56
c.14.23.120.8
Solution
a. The first byte is 227 (between 224 and 239); the class is D.
b. The first byte is 193 (between 192 and 223); the class is C.
c. The first byte is 14 (between 0 and 127); the class is A.
d. The first byte is 252 (between 240 and 255); the class is E.
e. The first byte is 134 (between 128 and 191); the class is B.
Subnet Addressing
• The network address is the beginning
address of each block. It can be found by
applying the default mask to any of the
addresses in the block (including itself). It
retains the netid of the block and sets the
hostid to zero.
Range of Addresses
• We often need to find the range of address
given to an organization.
– Find the number of addresses if first and last
are given: 146.102.29.0 and 146.102.32.255
– There are 256 addresses in the last octet. For
the third octet 32. There are 256 addresses
in 29, 30, 31 (and 32) for a total of 256*4 =
1024 addresses.
Finding the first and last address given
one IP address and the mask
• To find the first IP address
– Keep the net portion the same, and turn all
host portions to 0.
• To find the last address:
– Keep the net portion the same, and turn all
host portion to 1s.
Find the first and last IP
• Given 73.22.17.25 and mask of 255.0.0.0.
find the first and last addresses.
– 73.0.0.0 and 73.255.255.255
– How many addresses are in the block?
16,777,216
Finding the network portion
• Given the IP address and mask, AND
• Default masks are:
– For class A 255.0.0.0
– For class B 255.255.0.0
– For class C 255.255.255.0
• However you can create any mask you
want based on some rules.
Finding first and last address
revisited
• Find the First address in the block
– IP address AND network mask
• Find the last address in the block
– IP address OR complement of network mask
Example 12
Given the address 23.56.7.91, find the beginning address
(network address).
Solution
The default mask is 255.0.0.0, which means that only the first
byte is preserved and the other 3 bytes are set to 0s. The
network address is 23.0.0.0.
Example 15
What is the subnetwork address if the destination address is
200.45.34.56 and the subnet mask is 255.255.240.0?
Solution
We apply the AND operation on the address and the subnet
mask.
Address
➡ 11001000 00101101 00100010 00111000
Subnet Mask
➡ 11111111 11111111 11110000 00000000
Subnetwork Address ➡ 11001000 00101101 00100000 00000000.
Figure 4.25
Comparison of a default mask and a subnet mask
Table 4.3 Special addresses
Private IPs
CIDR notation
• Classless Inter-Domain routing (CIDR)
CIDR
• CIDR is an alternative to traditional IP
subnetting that organizes IP addresses
into subnetworks independent of the value
of the addresses themselves. CIDR is also
known as supernetting as it effectively
allows multiple subnets to be grouped
together for network routing.
• Ddd.ddd.ddd.ddd/m 192.5.48.69/26
CIDR addressing
• In the address 167.199.170.82/27 the
network mask is 255.255.255.224 (27
ones and five zeros).
• The suffix length of 5, meaning there can
be 32 host addresses.
• We can find the first address by ANDING
the IP with mask. We can find the last
address by ORing the address with the
complement of the mask.
CIDR
• Prefix length is given after the slash
• 230.8.24.56/16 gives block of 230.8.0.0 to 230.8.255.255
• To find the first address AND the mask.
• To find the last address, find the complement of the mask, then OR.
CIDR example
• One of the address in a block is 17.63.110.114/24. Find the number
of address, the first address, and the last address of the block.
17
63 110 114
255 255 255
0 AND
17
63 110
0 IS THE FIRST ADDRESS
--17
63 110 114
0
0
0 255 OR
17 63 110 255 IS THE LAST ADDRESS
CIDR example
• 110.23.120.14/20. Find the first and last
address
110
23 120 14
255
255 240 0 AND
110
23 112 0
110
0
110
23
0
23
120 14
15 255 OR
127 255 LAST ADDRESS
Supernetting
• Class C network addresses are still
available, but one may not be enough for
an organization.
• In supernetting we can combine several
class C blocks to create a larger range of
addresses.
• If an organization needs 1000 addresses,
we can join 4 class C blocks.
Supernet masks
• For Supernetting we go backwards with
the subnet mask. In this case we have 2
less 1s than the default subnet mask.
• The default subnet mask for class C is
255.255.255.0. In this case we go 2 bits
to the left, or 255.255.252.0.
• In superneting, the number of blocks to
combine needs to be a power of 2.