CS4500CS4500 Dr. ClincyLecture1 Lecture #2 Chapter 5: Addressing (Part 2 of 3)

CS4500CS4500 Dr. ClincyLecture2 Multihomed devices As we mentioned, any device with one or more connections to the Internet will need an IP address for EACH connection – such devices are called “multihomed” devices. A Router could be a multihomed device

CS4500CS4500 Dr. ClincyLecture3 Example of direct broadcast address Example of limited broadcast address If the hostid is all 1’s, it’s called a “broadcast address” and the router use it to send a packet to all host in a specific network. In this case, hosts 20, 64, 126 and etc. will receive the packet from the router If the hostid and netid are all 1’s, it’s called a “limited broadcast address”. If the host wants to send a packet to all host in a specific network, it would use this address. The router would block this address so that data stays contained within a specific network. Router sending to all hosts on a network Host sending to all other hosts on a network

CS4500CS4500 Dr. ClincyLecture4 Example of this host on this address Example of specific host on this network An address of all 0’s is used during bootstrap time if the host doesn’t know it’s IP address. The un-named host sends an all 0 source address and limited broadcast (all 1’s) destination address to the bootstrap server. An address with a netid of all 0’s is used by a host or router to send another host with in the same network a message. Host sending to some other specific host on a network IP-less Host sending message to bootstrap server

CS4500CS4500 Dr. ClincyLecture5 Example of loopback address The IP address with the 1 st byte equal to 127 is used for the loop back address. Loopback address is used to test software on a machine – the packet never leaves the machine – it returns to the protocol software Example: a “ping” command can send a packet with a loopback address as the destination address to see if the IP software is capable of receiving and processing a packet.

CS4500CS4500 Dr. ClincyLecture6 Sample internet Token Ring ATM Ethernet

CS4500CS4500 Dr. ClincyLecture7 Chapter 5 Subnetting

CS4500CS4500 Dr. ClincyLecture8 SUBNETTING When we talked about CLASSFUL addressing – we realized the problem of wasted host addresses and depleting available network addresses. In subnetting, a network is divided into several smaller networks called subnetworks or subnets – each subnet will have it’s own address Typically, there are 2 steps in reaching a destination: first we must reach the network (netid) and then we reach the destination (hostid)

CS4500CS4500 Dr. ClincyLecture9 A network with two levels of hierarchy (not subnetted) The 2 level approach is not enough some times – you can only have 1 physical network – in example, all host are at the same level – no grouping

CS4500CS4500 Dr. ClincyLecture10 A network with three levels of hierarchy (subnetted) With subnetting, hosts can be grouped (0-63)(64-127) ( ) ( )

CS4500CS4500 Dr. ClincyLecture11 Addresses in a network with and without subnetting With subnetting, there are 3 levels (versus 2 levels). Partition the hostid space into subnetid and hostid. (1 st ) network, (2 nd ) subnetwork and (3 rd ) host

CS4500CS4500 Dr. ClincyLecture12 Similar to Hierarchy concept in a telephone number

CS4500CS4500 Dr. ClincyLecture13 Default mask and subnet mask

CS4500CS4500 Dr. ClincyLecture14 Finding the Subnet Address Given an IP address, we can find the subnet address the same way we found the network address in the previous chapter. We apply the mask to the address. We can do this in two ways: straight or short-cut. Straight Method In the straight method, we use binary notation for both the address and the mask and then apply the AND operation to find the subnet address. Short-Cut Method ** If the byte in the mask is 255, copy the byte in the address. ** If the byte in the mask is 0, replace the byte in the address with 0. ** If the byte in the mask is neither 255 nor 0, we write the mask and the address in binary and apply the AND operation.

CS4500CS4500 Dr. ClincyLecture15 Subnet Mask Form In the early days, non-contiguous 1’s masks were used (0’s and 1’s could alternate) Today, as a best practice, contiguous 1’s masks are used In either case, the black box can perform the “masking” process

CS4500CS4500 Dr. ClincyLecture16 Example 1 What is the subnetwork address if the destination address is and the subnet mask is ? Solution The subnetwork address is

CS4500CS4500 Dr. ClincyLecture17 1-bit Netid case (no subnets) 16 addresses/block Number of blocks: 2 Address range per block: 0 to 15 Netids: 0, 1 Network Addresses : 00000, Broadcast Addresses: 01111, Recall - 5-bit Address Space Illustration

CS4500CS4500 Dr. ClincyLecture18 1-bit Subnet case Number of blocks/networks: 2 Number subnets per block: 2 8 addresses/subnet Address range per subnet: 0 to 7 Subnet ids: 0, 1 Network Addresses : 00000, 01000, 10000, Broadcast Addresses: 00111, 01111, 10111, bit Address Space Illustration subnet

CS4500CS4500 Dr. ClincyLecture19 2-bit Subnet case Number of blocks/networks: 2 Number subnets per block: 4 4 addresses/subnet Address range per subnet: 0 to 3 Subnet ids: 00, 01, 10, 11 Network Addresses : 00000, 00100, 01000, , 10100, 11000, Broadcast Addresses: 00011, 00111, 01011, , 10111, 11011, bit Address Space Illustration subnet

CS4500CS4500 Dr. ClincyLecture20 What is the mask ? If address is masked, what is the result ? Illustrating the mask concept (1 of 3) netid address result

CS4500CS4500 Dr. ClincyLecture21 Illustrating the mask concept (2 of 3) subnet What is the mask (subnet mask) ? If address is masked, what is the result ? address result

CS4500CS4500 Dr. ClincyLecture22 Illustrating the mask concept (3 of 3) subnet What is the mask (subnet mask) ? If address is masked, what is the result ? address result

CS4500CS4500 Dr. ClincyLecture23 Example 2 What is the subnetwork address if the destination address is and the mask is ?

CS4500CS4500 Dr. ClincyLecture24 Comparison of a default mask and a subnet mask A portion of the hostid space is divided between some contiguous 1’s and 0’s

CS4500CS4500 Dr. ClincyLecture25 The number of subnets must be a power of 2. Determine the number of subnets added by looking at the number of 1s added to the default mask and performing 2 raised to that number For example, 2 3 = 8 subnets

CS4500CS4500 Dr. ClincyLecture26 Example 3 A company is granted the site address (class C). The company needs six subnets. Design the subnets. Solution The number of 1s in the default mask is 24 (class C). The company needs six subnets. This number 6 is not a power of 2. The next number that is a power of 2 is 8 (2 3 ). We need 3 more 1s in the subnet mask. The total number of 1s in the subnet mask is 27 (24  3). The total number of 0s is 5 (32  27). The mask would be

CS4500CS4500 Dr. ClincyLecture27 Solution (Continued) or The number of subnets is 8. The number of addresses in each subnet is 2 5 (5 is the number of 0s) or 32.

CS4500CS4500 Dr. ClincyLecture28 Example 3

CS4500CS4500 Dr. ClincyLecture29 Example 4 A company is granted the site address (class B). The company needs 1000 subnets. Design the subnets. Solution The number of 1s in the default mask is 16 (class B). The company needs 1000 subnets. This number is not a power of 2. The next number that is a power of 2 is 1024 (2 10 ). We need 10 more 1s in the subnet mask. The total number of 1s in the subnet mask is 26 (16  10). The total number of 0s is 6 (32  26). The mask is or The number of subnets is The number of addresses in each subnet is 2 6 (6 is the number of 0s) or 64.

CS4500CS4500 Dr. ClincyLecture30 Example 4 Subtract 63 from 255 to get 192