TCP/IPTCP/IP Dr. ClincyLecture1 Chapter 5: Addressing (Part 2 of 3) Agenda Special Addresses Classful - Subnetting Classful - Supernetting

TCP/IPTCP/IP 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

TCP/IPTCP/IP 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

TCP/IPTCP/IP 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

TCP/IPTCP/IP 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 – it checks your NIC and TCP/IP 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.

TCP/IPTCP/IP Dr. ClincyLecture6 Chapter 5 Subnetting

TCP/IPTCP/IP Dr. ClincyLecture7 SUBNETTING When we talked about CLASSFUL addressing – we realized the problem of wasted host addresses and depleting available network addresses. Why wasted addresses ? Because there is a single “owner” of the entire block – block can’t be shared with other “owners” In subnetting, a network is divided into several smaller “autonomous or self-contained” networks called subnetworks or subnets – each subnet will have it’s own set of addresses Typically, there are 2 steps in reaching a destination: first we must reach the network (netid) and then we reach the destination (hostid) With subnets, there could be atleast 3 steps, (1) netid, (2) subnet id, and (3) hostid

TCP/IPTCP/IP Dr. ClincyLecture8 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

TCP/IPTCP/IP Dr. ClincyLecture9 A network with three levels of hierarchy (subnetted) With subnetting, hosts can be grouped (0-63)(64-127) ( ) ( )

TCP/IPTCP/IP Dr. ClincyLecture10 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

TCP/IPTCP/IP Dr. ClincyLecture11 Similar to Hierarchy concept in a telephone number

TCP/IPTCP/IP Dr. ClincyLecture12 Default mask and subnet mask

TCP/IPTCP/IP Dr. ClincyLecture13 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.

TCP/IPTCP/IP Dr. ClincyLecture14 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

TCP/IPTCP/IP Dr. ClincyLecture15 Example 1 What is the subnetwork address if the destination address is and the subnet mask is ? Solution The subnetwork address is

TCP/IPTCP/IP Dr. ClincyLecture16 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

TCP/IPTCP/IP Dr. ClincyLecture17 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

TCP/IPTCP/IP Dr. ClincyLecture18 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

TCP/IPTCP/IP Dr. ClincyLecture19 What is the mask ? If address is masked, what is the result ? Illustrating the mask concept (1 of 3) netid address result

TCP/IPTCP/IP Dr. ClincyLecture20 Illustrating the mask concept (2 of 3) subnet What is the mask (subnet mask) ? If address is masked, what is the result ? address result

TCP/IPTCP/IP Dr. ClincyLecture21 Illustrating the mask concept (3 of 3) subnet What is the mask (subnet mask) ? If address is masked, what is the result ? address result

TCP/IPTCP/IP Dr. ClincyLecture22 Example 2 What is the subnetwork address if the destination address is and the mask is ?

TCP/IPTCP/IP Dr. ClincyLecture23 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

TCP/IPTCP/IP Dr. ClincyLecture24 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

TCP/IPTCP/IP Dr. ClincyLecture25 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

TCP/IPTCP/IP Dr. ClincyLecture26 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.

TCP/IPTCP/IP Dr. ClincyLecture27 Example 3

TCP/IPTCP/IP Dr. ClincyLecture28 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.

TCP/IPTCP/IP Dr. ClincyLecture29 Example 4 Subtract 63 from 255 to get 192

TCP/IPTCP/IP Dr. ClincyLecture30 SUPERNETTING Although class A and B addresses are dwindling – there are plenty of class C addresses The problem with C addresses is, they only have 256 hostids – not enough for any midsize to large size organization – especially if you plan to give every computer, printer, scanner, etc. multiple IP addresses Supernetting allows an organization the ability to combine several class C blocks in creating a larger range of addresses Note: breaking up a network = subnetting Note: combining Class-C networks = supernetting

TCP/IPTCP/IP Dr. ClincyLecture31 Assigning or Choosing Class C Blocks When assigning class C blocks, there are two approaches: (1) random and (2) superblock Random Approach: the routers will see each block as a separate network and therefore, for each block there would be an entry in the routing table – a router contains an entry for each destination network Superblock Approach: instead of multiple routing table entries, there would be a single entry. However, the choices of blocks need to follow a set of rules: #1 – the # of blocks must be a power of 2 (ie. 1, 2, 4, 8 …) #2 – blocks must be contiguous (no gaps between blocks) #3 – the 3 rd byte of the first address in the superblock must be evenly divisible by the number of blocks – ie. if the # of blocks is N, the 3 rd byte must be divisible by N

TCP/IPTCP/IP Dr. ClincyLecture32 Example 5 A company needs 600 addresses. Which of the following set of class C blocks can be used to form a supernet for this company? Solution 1: No, there are only three blocks. Must be a power of 2 2: No, the blocks are not contiguous. 3: No, 31 in the first block is not divisible by 4. 4: Yes, all three requirements are fulfilled. (1. Power of 2, 2. Contiguous and 3. 3 rd byte of 1 st address is divisible by 4: 32/4=8)

TCP/IPTCP/IP Dr. ClincyLecture33 Example 8 A supernet has a first address of and a supernet mask of How many blocks are in this supernet and what is the range of addresses? Solution The default mask has 24 1s because is a class C. Because the supernet mask is , the supernet has 21 1s. Since the difference between the default and supernet masks is 3, there are 2 3 or 8 blocks in this supernet. Because the blocks start with and must be contiguous, the blocks are , , ……… The first address is The last address is The total number of addresses is 8 x 256 = 2048

TCP/IPTCP/IP Dr. ClincyLecture34 Explain Supernetting Conceptually Back out this bit from netid into host id Causes these 2 blocks to combine as a single block