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Addressing Multihomed Devices

Learn about addressing for multihomed devices and the different types of addresses used, such as direct broadcast, limited broadcast, IP-less, and loopback addresses.

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Addressing Multihomed Devices

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  1. Lecture #2 Chapter 5: Addressing (Part 2 of 3) Lecture

  2. 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 Lecture

  3. Example of direct broadcast address Router sending to all hosts on a network 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 Example of limited broadcast address Host sending to all other hosts on a network 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. Lecture

  4. Example of this host on this address IP-less Host sending message to bootstrap server 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. Example of specific host on this network Host sending to some other specific host on a network 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. Lecture

  5. Example of loopback address • The IP address with the 1st 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. Lecture

  6. Sample internet Ethernet ATM Token Ring Ethernet Lecture

  7. Chapter 5 Subnetting Lecture

  8. 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) Lecture

  9. A network with two levels ofhierarchy (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 Lecture

  10. A network with three levels of hierarchy (subnetted) (0-63) (64-127) With subnetting, hosts can be grouped (128-191) (192-255) Lecture

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

  12. Similar to Hierarchy concept in a telephone number Lecture

  13. Default mask and subnet mask Lecture

  14. 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. Lecture

  15. 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 Lecture

  16. Example 1 What is the subnetwork address if the destination address is 200.45.34.56 and the subnet mask is 255.255.240.0? Solution 11001000 00101101 00100010 00111000 11111111 11111111 1111000000000000 11001000 00101101 0010000000000000 The subnetwork address is 200.45.32.0. Lecture

  17. Recall - 5-bit Address Space Illustration 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, 10000 Broadcast Addresses: 01111, 11111 Lecture

  18. 5-bit Address Space Illustration subnet 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, 11000 Broadcast Addresses: 00111, 01111, 10111, 11111 Lecture

  19. 5-bit Address Space Illustration subnet 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, 01100 10000, 10100, 11000, 11100 Broadcast Addresses: 00011, 00111, 01011, 01111 10011, 10111, 11011, 11111 Lecture

  20. Illustrating the mask concept (1 of 3) netid What is the mask ? 10000 If address 11101 is masked, what is the result ? result address 1 0 0 0 0 Lecture

  21. Illustrating the mask concept (2 of 3) subnet What is the mask (subnet mask) ? 11000 If address 11101 is masked, what is the result ? result address 1 1 0 0 0 Lecture

  22. Illustrating the mask concept (3 of 3) subnet What is the mask (subnet mask) ? 11100 If address 11101 is masked, what is the result ? result address 1 1 1 0 0 Lecture

  23. Example 2 What is the subnetwork address if the destination address is 19.30.84.5 and the mask is 255.255.192.0? Lecture

  24. 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 Lecture

  25. 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, 23 = 8 subnets Lecture

  26. Example 3 A company is granted the site address 201.70.64.0 (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 (23). 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 Lecture

  27. Solution (Continued) • 11111111 11111111 1111111111100000 • or • 255.255.255.224 • The number of subnets is 8. • The number of addresses in each subnet is 25 (5 is the number of 0s) or 32. Lecture

  28. Example 3 Lecture

  29. Example 4 A company is granted the site address 181.56.0.0 (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 (210). 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 11111111 11111111 1111111111000000 or 255.255.255.192. The number of subnets is 1024. The number of addresses in each subnet is 26 (6 is the number of 0s) or 64. Lecture

  30. Example 4 Subtract 63 from 255 to get 192 Lecture

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