Chapters 4 & 5 Addressing

1. Chapters 4 & 5 Addressing Lecture

2. Recall, what info is used by router to make next hop decision ? What ACTUAL info does the router use to make a next hop decision ? Lecture

3. Mask • Given the network address, we can easily determine the block and range of addresses • Suppose given the IP address, can we determine the network address (beginning of the block) ? • To route packets to the correct network, a router must extract the network address from the destination IP address • For example, given 134.45.78.2, we know this is a class B, therefore 134.45 is the netid and 134.45.0.0 is the network address (starting address of the block) • How would we EXTRACT the network address from the IP address? We would use a MASK. A mask is a 32-bit binary number that gives the first address in the block (the network address) when bitwise ANDed with an address in the block. Lecture

4. AND operation • If bit is ANDed with 1, it’s preserved • If bit is ANDed with 0, it’s changed to a 0. • There are 3 default masks: one for each class. The default masks preserve the netid when ANDed with the addresses • Class A Default Mask: 255.0.0.0 • Class B Default Mask: 255.255.0.0 • Class C Default Mask: 255.255.255.0 • A simple way to determine the netid for un-subnetted cases: (1) if mask byte is 255, retain corresponding byte of the address, (2) if mask byte is 0, set corresponding address byte to 0. Lecture

5. Examples Given the address 23.56.7.91 and the default class A mask, find the beginning address (network address). The default mask is 255.0.0.0, which means that only the first byte is preserved and the other 3 bytes are set to 0s. The network address is 23.0.0.0. Solution Given the address 132.6.17.85 and the default class B mask, find the beginning address (network address). The default mask is 255.255.0.0, which means that the first 2 bytes are preserved and the other 2 bytes are set to 0s. The network address is 132.6.0.0. Solution Given the address 201.180.56.5 and the class C default mask, find the beginning address (network address). The default mask is 255.255.255.0, which means that the first 3 bytes are preserved and the last byte is set to 0. The network address is 201.180.56.0. Solution Lecture

6. 5-bit Address Space Illustration No Netid case 32 addresses/block Number of blocks: 1 Address range per block: 0 to 31 Netids: N/A Network Addresses : 00000 Broadcast Addresses: 11111 Lecture

7. 5-bit Address Space Illustration 1-bit Netid case 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 What is the mask ? Lecture

8. 5-bit Address Space Illustration 2-bit Netid Case 8 addresses/block Number of blocks: 4 Address range per block: 0 to 7 Netids: 00, 01, 10, 11 Network Addresses : 00000, 01000, 10000, 11000 Broadcast Addresses: 00111, 01111, 10111, 11111 What is the mask ? Lecture

9. 5-bit Address Space Illustration 3-bit Netid Case 4 addresses/block Number of blocks: 8 Address range per block: 0 to 3 Netids: 000, 001, 010, 011, 100, 101, 110, 111 Network Addresses : 00000, 00100, 01000, 01100 10000, 10100, 11000, 11100 Broadcast Addresses: 00011, 00111, 01011, 01111 10011, 10111, 11011, 11111 What is the mask ? Lecture

10. Mixing 3-bit & 2-bit Cases (think of the 32-bit case) 4 addresses/block and 8 addresses/block Number of blocks: 6 Address range per block: 0 to 3 and 0 to 7 Netids: 000, 001, 010, 011, 10, 11 Network Addresses : 00000, 00100, 01000, 01100 10000, 11000 Broadcast Addresses: 00011, 00111, 01011, 01111 10111, 11111 Lecture

11. Multihomed devices • As we mentioned that, 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

12. 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

13. Example of this host on this address IPless 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

14. 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

15. Sample internet Ethernet ATM Token Ring Ethernet With your new found knowledge, think about Project 2 Lecture

16. Subnetting Lecture

17. 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

18. 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

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

20. 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

21. Similar to Hierarchy concept in a telephone number Lecture

22. Default mask and subnet mask Lecture

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. Example 3 Lecture