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

2. Addressing
Physical
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. 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

5. 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

6. Finding the address class

7. Figure 4.5 Finding the class in decimal notation

8. 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.

9. 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.

10. Subnets Makes smaller networks for better security and easy management
Mask is used by routers to find the network portion of the address. AND operation.

11. Creating subnet masks Determine how many subnets you need
How many bits would be required to create that many subnets?
For example you need 8 subnets, need 3 bits set aside. Certain addresses are reserved, so all subnets can’t be used.
Turn those bits (msb) to 1.
For example class C, default subnet is , if you decided to subnet it to 8 subnets, then you would use the subnet I will explain in class.

12. 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

13. 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 ➡

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

15. Table 4.3 Special addresses
Private IPs

16. CIDR notation Classless Inter-Domain routing (CIDR)
Ddd.ddd.ddd.ddd/m /26
Used for subnetting and supernetting
An ISP can now subdivide a larger blocks and hand out 1, 2, 4, 8,.. (power of 2) to the customers. These are called variable length bocks and we use a slash notation.

17. Slash notation
In classless addressing we need to include the prefix length to each address if we need to find the block of the address.
Given the address /27 the netmask is (27 ones).

18. Calculations
Given the address /20 find the number of address, the first and last address in the block
There are 20 1s. So ? is The mask is
Number of addresses is 32-20, so 212 or 4096
To find the first address AND the given address with the mask AND = (third octet (120) AND (240)
To find the last address: OR the address with the complement of the mask (also we can keep all the left most bits of the IP and change the 12 rightmost to 1s.

19. /22
Mask is
First IP AND = =
Number of IP is = =1024
Last

20. Block Assignment
The number of IP addresses requested should be power of 2
The requested block needs to be allocated where there are a contiguous number of unallocated addresses in the address space.
Suppose a block of 1000 IP requested.
Power of 2 is 210 which is 1024.
Prefix length is which is 22.
From the available address space, say /22 (which is divisible by 1024) is given. Last address is

21. Special addresses
All zeros – When a device does not know its on IP address, it requests one using this address as the source and sends a limited broadcast asking for an IP. Therefore, all zeros means, me.
All ones. Limited broadcast address in the current network.
Loopback address is localhost. Used to test a software on a machine.