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.

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.

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.

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) 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.

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).

Calculations Given the address /20 find the number of address, the first and last address in the block –There are 20 1s. So ? is 240. The mask is –Number of addresses is 32-20, so 2 12 or 4096 –To find the first address AND the given address with the mask AND = (third octet AND –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.

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

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 2 10 which is –Prefix length is which is 22. –From the available address space, say /22 (which is divisible by 1024) is given. Last address is

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.