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There are 2 32 possible IPv4 addresses.

Background to Chapter 9 - Classless and Subnet Address Extensions (CIDR) and Chapter 31 – A Next-Generation IP. There are 2 32 possible IPv4 addresses. When the predecessor of the Internet started in the 1970s it did not seem possible that this address space would ever be exhausted.

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There are 2 32 possible IPv4 addresses.

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  1. Background to Chapter 9 - Classless and Subnet Address Extensions (CIDR) and Chapter 31 – A Next-Generation IP There are 232 possible IPv4 addresses. When the predecessor of the Internet started in the 1970s it did not seem possible that this address space would ever be exhausted. No effort was made to allocate IP addresses carefully. In particular: ● The classful addressing system was wasteful (224 addresses to MIT) ● Every physical network had to have a unique network prefix ● Network prefixes were not allocated geographically (example – 138.26.0.0 is UAB 138.25.0.0 is in Australia) 1

  2. Comer: “In the early 1980s, as Ethernet gained popularity, it became apparent that the classful addressing scheme would have insufficient network addresses, especially class B prefixes.” 1985: Subnetting allowed organizations to share a single network prefix over multiple physical networks, which helped conserve the IPv4 address space (Comer, Chapter 9A). 1993: Shortage of IPv4 network addresses threatens, especially class B. Some geographical allocation of class-C addresses Supernetting/CIDR comes to the rescue, superseding “classfull” addressing (Comer, Chapter 9B). Present situation: ● The IPv4 address space is exhausted – no new large blocks left ● Forwarding tables in the Internet backbone are very large (200,000 entries). 2012 Large-scale adoption of IPv6 (Comer chapter 31) 2

  3. Recall: Figure 4.1 Figure 9.3 Subnetting class B network 3

  4. 9.16 Classless Addressing and Supernetting Under the original “classful” addressing system IPv4 address space was becoming exhausted. The rigid class scheme made allocation of IP addresses inefficient. Subnet addressing (1987) helped, but problem remained. “Temporary” solution (1993) was to abandon classes completely and let the network prefix be any length. We already had the ability to do this, in the address mask! This is called classless IP addressing, or supernetting. 4

  5. 9.16 Classless Addressing and Supernetting - continued Example: Organization wants a class-B network address – none available. 256 class-C networks would have the same total number of addresses. Problem: Outsiders would need 256 entries in their routing tables, instead of one (contrast subnetting, which is invisible to outsiders). Solution: Classless Inter-Domain Routingaggregates 256 contiguous class-C networks together by carrying along a netmask of 255.255.0.0 (“treat these 256 contiguous class-C networks like a class-B network”) The network address is never mentioned without also stating the netmask. Problem with implementation of this: software on all external routers had to be modified. 5

  6. 9.17 CIDR Address Blocks and Bit Masks The netmask 255.255.0.0 is just one example. The division between the network part and the host part of the IP address can be placed (almost) anywhere by an appropriate address mask. CIDR notation: State number of bits in network part. e.g. address mask 255.255.255.0 is CIDR /24 6

  7. 9.17 CIDR Address Blocks and Bit Masks – continued The revised forwarding algorithm remains unchanged, but is now used both internally and externally. 7 Figure 9.7

  8. 9.17 CIDR Address Blocks and Bit Masks – continued CIDR allows allocation of different sizes of address blocks. It was introduced in the context of privatization of the Internet, which introduced Internet Service Providers (ISPs). Using CIDR, large ISPs are allocated large address blocks, which they can then divide (using CIDR) into smaller blocks to allocate to their customers. 8

  9. 9.17 CIDR Address Blocks and Bit Masks – continued Example: Organization is assigned a block of 2048 addresses, based on 128.211.168.0 (notice ambiguous class – under classful system 128.211 is class-B 64K addresses allocated as a single block) Block size is 211 addresses, which would have been 8 class C networks. Netmask for this block is 11111111 11111111 11111000 00000000 255 . 255 . 248 . 0 CIDR /21 Refer to this allocation as 128.211.168.0 /21 9

  10. 9.17 CIDR Address Blocks and Bit Masks - continued Figure 9.9 10

  11. 9.18 Address Blocks and CIDR Notation Possible address masks: Class C Class A Class B /31 and /32 useless! Figure 9.10 11

  12. 9.19 A Classless Addressing Example A large ISP has been allocated the entire class-B address 128.211.0.0 i.e. 128.211.0.0 /16 Large ISP has allocated the address block shown previously to a smaller ISP, i.e. 128.211.168.0 /21 128.211.10101000.00000000 So smaller ISP has available 128.211.168.0 128.211.169.0 128.211.170.0 128.211.171.0 128.211.172.0 128.211.173.0 128.211.174.0 128.211.175.0 12

  13. 9.19 A Classless Addressing Example - continued 128.211.168.0 /21 Expands to: 3rd octet 4th octet 128.211.168.0 10101 000 00000000 128.211.169.0 10101 001 128.211.170.0 10101 010 128.211.171.0 10101 011 128.211.172.0 10101 100 128.211.173.0 10101 101 128.211.174.0 10101 110 128.211.175.0 10101 111 128.211.168.0/22 128.211.172.0/23 /24 /24 13

  14. Smaller ISP has been allocated 128.211.168.0/21 Can allocate partitions to customers: 256 addresses 128.211.175.0/24 256 addresses 128.211.174.0/24 1024 addresses 128.211.168.0/22 512 addresses 128.211.172.0/23 The smaller ISP could further partition 128.211.175.0/24 14

  15. 9.19 A Classless Addressing Example - continued An ISP owning 128.211.0.0/16 might assign an individual needing only two IP addresses 128.211.176.212 /30 (note that this is not in the range of the previous example) Figure 9.11 The two IP usable addresses are: 128.211.176.213 and 128.211.176.214 15

  16. 9.19 A Classless Addressing Example - continued Classless addressing, which is now used throughout the Internet, treats IP addresses as arbitrary integers, and allows a network administrator to partition addresses into contiguous blocks, where the number of addresses in a block is a power of 2. 16

  17. 9.21 Longest-Match and Mixtures of Route Types Consider the smaller ISP’s routers – entry router is R0 From R0 assume that all networks except 128.211.175.0 /24 are reached through router R1 and 128.211.175.0 /24 is reached through R2 3rd octet4th octet 128.211.168.0 10101 000 00000000 128.211.169.0 10101 001 128.211.170.0 10101 010 128.211.171.0 10101 011 128.211.172.0 10101 100 128.211.173.0 10101 101 128.211.174.0 10101 110 128.211.175.0 10101 111 Fwd to R1 Fwd to R2 17

  18. 9.19 A Classless Addressing Example – continued Smaller ISP has been allocated 128.211.168.0/21 256 addresses 128.211.175.0/24 R2 256 addresses 128.211.174.0/24 1024 addresses 128.211.168.0/22 512 addresses 128.211.172.0/23 18

  19. 9.21 Longest-Match and Mixtures of Route Types – continued 3rd octetR0 table entry 128.211.168.0 10101 000 128.211.169.0 10101 001 128.211.170.0 10101 010 128.211.171.0 10101 011 128.211.172.0 10101 100 128.211.173.0 10101 101 128.211.174.0 10101 110 128.211.168.0/21 to R1 128.211.175.0/24 to R2 128.211.175.0 10101 111 Nothing gets forwarded to R2 19

  20. 9.21 Longest-Match and Mixtures of Route Types– continued Figure 9.14 All traffic will be sent to 10.0.0.2 20

  21. 9.21 Longest-Match and Mixtures of Route Types – continued Conclusion: We need another modification to the forwarding algorithm: Forward on basis of longest match in routing table Can help by putting the most specific routes first. 21

  22. 9.22 CIDR Blocks Reserved for Private Networks Figure 9.15 22

  23. IP Address Allocation: Internet Assigned Numbers Authority “owns” the entire IPv4 and IPv6 address space! Regional Internet Registries

  24. Allocation of IP addresses (IPv4 and IPv6) mentioned briefly in Comer’s chapter 4 ARIN Large ISP Large end-user or small ISP

  25. Exhaustion of IPv4 Address Space February 01, 2011 The Internet Assigned Numbers Authority (IANA) assigned two of the remaining blocks of IPv4 addresses - each containing 16.7 million addresses - to the Asia Pacific Network Information Centre (APNIC) on Tuesday. This action sparks an immediate distribution of the remaining five blocks of IPv4 address space, with one block going to each of the five Regional Internet Registries (RIR). The American Registry for Internet Numbers (ARIN), which doles out IPv4 addresses to carriers and other network operators in North America, is expected to receive its last allotment of IPv4 addresses today. Experts say it will take anywhere from three to seven months for the registries to distribute the remaining IPv4 addresses to carriers. 26 No more new blocks of IPv4 addresses!

  26. Advent of IPv6: World IPv6 Day, 2011 On 8 June, 2011, top websites and Internet service providers around the world, including Google, Facebook, Yahoo!, Akamai and Limelight Networks joined together with more than 1000 other participating websites in World IPv6 Day for a successful global-scale trial of the new Internet Protocol, IPv6. By providing a coordinated 24-hour “test flight”, the event helped demonstrate that major websites around the world are well-positioned for the move to a global IPv6-enabled Internet, enabling its continued exponential growth. World IPv6 Launch, 2012 Major ISPs, home networking equipment manufacturers, and web companies around the world are coming together to permanently enable IPv6 for their products and services by 6 June 2012.

  27. Chapter 31 - A Next Generation IP (IPv6) 31.6 Features of IPv6 Not backward compatible with IPv4!Operate Dual stacks ● Larger Addresses (128-bit) ● Extended Address Hierarchy ● Flexible Header Format ● Improved Options 28

  28. Recall IPv4 Datagram Header Format 29

  29. 31.7 General Form of an IPv6 Datagram 30

  30. 4 6 31

  31. 31.8 IPv6 Base Header Format Changes from IPv4 ● Alignment has been changed from 32-bit to 64-bit ● Header Length field has been replaced by Payload Length (base header fixed length of 40 bytes) ●Address fields now 16 octets (128-bits) ● Fragmentation information moved out of fixed header into extension ● TIME-TO-LIVE replaced by HOP LIMIT ● SERVICE TYPE field renamed TRAFFIC CLASS and extended with a FLOW LABEL field ● PROTOCOL field replaced by NEXT HEADER field ● No HEADER CHECKSUM field 32

  32. 31.10 Parsing an IPv6 Datagram Simple case: If source routing specified: If Payload Authentication also specified: Hop-by-hop headers precede end-to-end headers. 33

  33. 31.11 IPv6 Fragmentation and Reassembly – omit 31.12 Consequences of End-to-End Fragmentation - omit 31.13 IPv6 Source Routing - omit 31.14 IPv6 Options - omit 34

  34. 31.15 Size of the IPv6 Address Space 296 times bigger than IPv4 address space! Every person on the planet can have a private internet the size of the present global Internet. 1024 addresses per square meter of the earth’s surface! Assigning all possible addresses at a rate of one million million per sec would take 1020 years. 35

  35. 31.16 IPv6 Colon Hexadecimal Notation Consider 128-bit address in dotted-decimal form: 104.230.140.100.255.255.255.255.0.0.17.128.150.10.255.255 In binary starts with 0110 1000 . 1110 0110 . 1000 1100 . 0110 0100 . 1111 1111 . 1111 1111 .. . Same 128-bit address in colon-hexadecimal form: 8 groups of 16 bits 68E6:8C64:FFFF:FFFF:0:1180:96A:FFFF Compression: FF05:0:0:0:0:0:0:B3 written as FF05::B3 (left-align what is to left of :: right-align what is to right) CIDR-like: 12AB::CD30:0:0:0:0 /60 means high-order 60 bits of address are (hexadecimal) 12AB00000000CD3 36

  36. 31.17 Three Basic IPv6 Address Types ● Unicast ● Anycast “The destination is a set of computers, possibly at different locations, that all share a single address; the datagram should be routed along a shortest path and delivered to exactly one of the group (i.e. the closest member) (used to duplicate DNS root servers under single IP address) ● Multicast 31.18 Duality of Broadcast and Multicast – omit 31.19 Engineering Choice and Simulated Broadcast - omit 37

  37. 31.20 Proposed IPv6 Address Space Assignment 38

  38. 31.21 Embedded IPv4 Addresses and Transition The 16-bit field contains 0000 if the host also has a “conventional” IPv6 address, FFFF if it does not. Transition: expect to run dual IPv4 IPv6 stacks for many years 39

  39. 31.22 Unspecified and Loopback Addresses 0:0:0:0:0:0:0:0 is an unspecified address (used at startup of a machine that does not yet have an assigned IPv6 address – same in IPv4) 0:0:0:0:0:0:0:1 is the loopback address (like 127.0.0.0 in IPv4) 40

  40. 31.23 Unicast Address Structure This will be a replacement for Comer’s treatment The replacement is based on a document by the American Registry for Internet Numbers (ARIN), September 2010. As stated earlier, authority for allocation of IPv6 addresses flows down the same hierarchy as IPv4: Internet Assigned Numbers Authority ARIN Large ISP Large end-user or small ISP 41

  41. Repeat Figure 31.8 (upper) The left half (64 bits) of the 128-bit address will be the Global Routing address, the right half of the address will be the Interface Identifier (i.e. MAC address) We now consider the further assignment of the leftmost 64 bits. 42

  42. Assignment of IPv6 unicast addresses 3 bits 61 bits 0 0 1 managed by IANA /3 3 20 41 Allocated by IANA 0 0 1 to ARIN managed by ARIN /23 3 20 9 32 Allocated by IANA Allocated by 0 0 1 to ARIN ARIN to large ISP managed by large ISP /32 3 20 9 16 16 Allocated by IANA Allocated by Assigned by ISP managed by 0 0 1 to ARIN ARIN to large ISP to large end-site end-site /48 43

  43. 3 20 9 16 16 Allocated by IANA Allocated by Assigned by ISP managed by 0 0 1 to ARIN ARIN to large ISP to large end-site end-site /48 3 20 9 24 8 Allocated by IANA Allocated by Assigned by ISP mgd. by 0 0 1 to ARIN ARIN to large ISP to small end-site end-site /56 3 20 9 32 Allocated by IANA Allocated by Assigned by ISP 0 0 1 to ARIN ARIN to large ISP to end-user /64 44

  44. The A-root server provides an example of IPv6 unicast addressing. IANA allocated ARIN this block of unicast IPv6 addresses: 2001: 400: /23 0010 0000 0000 0001 0000 0100 0000 0000 ….. High-order 23 bits allocated TO ARIN, rest of address assigned BY ARIN A-root server IPv6 address: 2001: 503: ba3e: [ 0: 0: 0: 2: 30] 0010 0000 0000 0001 0000 0101 0000 0011 1011 1010 0011 1110 ….. The A-root server IPv6 address was assigned by ARIN. Similarly, the K-root server IPv6 address was assigned by RIPE. 45

  45. 31.24 Interface Identifiers The expanded address space allows the interface hardware (MAC) address to be embedded in the IPv6 address. 46

  46. 31.24 Interface Identifiers– contd. The EUI-64 standard specifies how a 48-bit Ethernet address can be expanded to 64 bits. Recall that the high-order 24 bits identify the manufacturer (“company”) Low order 24 bits are serial number (“manufacturer’s extension”) F F F E Fig 31.11 This is used in IPv6 Link-Local Addresses 47

  47. 31.25 Local Addresses “In addition to the global unicast addresses described above, IPv6 includes prefixes for unicast addresses that have local scope …” These are link-local addresses restricted to the local network (IPv6 datagrams so addressed cannot cross a router). The first 10 bits are (from fig. 31.8) 1111 1110 10 If the following 6 bits are zero, this would be hexadecimal FE80 The low-order 64 bits encode the interface’s hardware address No need for ARP in IPv6! Example from network lab machine F1: Ethernet address: 00:B0:D0:63:5B:92 Link-local address: FE80::2B0:D0FF:FE63:5B92 48

  48. Ethernet address: 00:B0:D0:63:5B:92 Link-local address: FE:80::2B0:D0FF:FE63:5B92 00000010 6 3 5 B 9 2 0 2 F F F E B 0 D 0 So the complete IPv6 address of eth1 on F1 is FE:80::2B0:D0FF:FE63:5B92 49

  49. 31.26 Autoconfiguration and Renumbering -omit END OF COURSE MATERIAL!!! 50

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