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

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 (2 7 ) 16,777, 216 (2 24 ) Class B ,384 (2 14 ) 65,536 (2 16 ) Class C ,097,1 52 (2 21 ) 256 (2 8 ) Class D (multicast)multicast 1110 not defined Class E (reserved) 1111 not defined

Finding the address class

Figure 4.5 Finding the class in decimal notation

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.

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.

Given the address , find the beginning address (network address). Example 12 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

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

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 /26

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.

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

CIDR example Find the first and last address AND OR LAST ADDRESS