1. Dr. John P. Abraham Professor UTPA
21-IP addressing
Dr. John P. Abraham
Professor
UTPA

2. Addressing
Physical –will discuss later
Logical

3. 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

4. Octets IP address is written in 4 octets with separating dots.
One of the UTPA CS address is:
What is this address in decimal notation?

5. 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

6. Size of Network Number Bit field
Class
Leading Bits
Size of Network Number Bit field
Size of Rest Bit field
Number of Networks
Addresses per Network
Start address
End address
Class A
    0
    8
    24
    128 (27)
    16,777,216 (224)
Class B
   10
    16
    16,384 (214)
    65,536 (216)
Class C
 110
    2,097,152 (221)
    256 (28)
Class D (multicast)
1110
    not defined
Class E (reserved)
1111

7. Finding the address class

8. Figure 4.5 Finding the class in decimal notation

9. Find the class of each address:
a b c d e
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.

10. LAN
The network portion of all IP addresses should be the same on all machines within a LAN
You can use VLAN to put machines from different networks together artificially.
All computers within a LAN can be made visible to others in the LAN

11. LAN One should be able to share files with others within the LAN
An user of the file should be able to MAP the directory and give a drive letter (in windows)
Anyone wanting to connect to machine that does not belong the LAN must go through a routing table (usually located within the Router)

12. 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.

13. 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: and
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.

14. 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.

15. Find the first and last IP
Given and mask of find the first and last addresses.
and
How many addresses are in the block? 16,777,216

16. Finding the network portion
Given the IP address and mask, AND
Default masks are:
For class A
For class B
For class C
However you can create any mask you want based on some rules.

17. 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

18. Example 12
Given the address , find the beginning address (network address).
Solution The default mask is , which means that only the first byte is preserved and the other 3 bytes are set to 0s. The network address is

19. Example 15
What is the subnetwork address if the destination address is and the subnet mask is ?
Solution We apply the AND operation on the address and the subnet mask.
Address ➡
Subnet Mask ➡
Subnetwork Address ➡

20. Figure 4.25 Comparison of a default mask and a subnet mask

21. Table 4.3 Special addresses
Private IPs

22. CIDR notation
Classless Inter-Domain routing (CIDR)

23. 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 /26

24. CIDR addressing
In the address /27 the network mask is (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.

25. CIDR Prefix length is given after the slash
/16 gives block of to
To find the first address AND the mask.
To find the last address, find the complement of the mask, then OR.

26. CIDR example
One of the address in a block is /24. Find the number of address, the first address, and the last address of the block.
AND
IS THE FIRST ADDRESS
--- OR
IS THE LAST ADDRESS

27. CIDR example 110.23.120.14/20. Find the first and last address
AND OR
LAST ADDRESS

28. 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.

29. 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 In this case we go 2 bits to the left, or
In superneting, the number of blocks to combine needs to be a power of 2.