**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)

Background to Chapter 9 - Classless and Subnet Address Extensions (CIDR) and Chapter 31 A Next-Generation IP 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)

**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 addressesPresent situation:

The IPv4 address space is exhausted no new large blocks left

Forwarding tables in the Internet backbone are very large (200,000 entries).Supernetting/CIDR comes to the rescue, superseding classfull addressing (Comer, Chapter 9B). 2012 Large-scale adoption of IPv6 (Comer chapter 31)

**Figure 4.1Figure 9.3Subnetting class B networkRecall:

**9.16 Classless Addressing and SupernettingUnder 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.This is called classless IP addressing, or supernetting.We already had the ability to do this, in the address mask!

**9.16 Classless Addressing and Supernetting - continuedExample:Organization wants a class-B network address none available.256 class-C networks would have the same total number of addresses.Problem with implementation of this: software on all external routers had to be modified.Problem:

Outsiders would need 256 entries in their routing tables, instead of one (contrast subnetting, which is invisible to outsiders).Solution:

Classless Inter-Domain Routing aggregates 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.

**9.17 CIDR Address Blocks and Bit MasksThe 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

**9.17 CIDR Address Blocks and Bit Masks continuedThe revised forwarding algorithm remains unchanged, but is now used both internally and externally.Figure 9.7

**9.17 CIDR Address Blocks and Bit Masks continuedCIDR 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.

**9.17 CIDR Address Blocks and Bit Masks continuedExample:Organization is assigned a block of 2048 addresses, based on 128.211.168.0(notice ambiguous class under classful system 128.211 is class-B64K addresses allocated as a single block)Block size is 211 addresses, which would have been 8 class C networks.Netmask for this block is11111111 11111111 11111000 00000000 255 . 255 . 248 . 0CIDR /21Refer to this allocation as 128.211.168.0 /21

**9.17 CIDR Address Blocks and Bit Masks - continuedFigure 9.9

**9.18 Address Blocks and CIDR NotationFigure 9.10Possible address masks:Class AClass BClass C/31 and /32 useless!

**9.19 A Classless Addressing ExampleA large ISP has been allocated the entire class-B address 128.211.0.0i.e. 128.211.0.0/16Large ISP has allocated the address block shown previously to a smaller ISP,i.e. 128.211.168.0/21So smaller ISP has available

128.211.168.0128.211.169.0128.211.170.0128.211.171.0128.211.172.0128.211.173.0128.211.174.0128.211.175.0128.211.10101000.00000000

**9.19 A Classless Addressing Example - continued128.211.168.0/21

Expands to:3rd octet 4th octet 128.211.168.01010100000000000128.211.169.010101 001128.211.170.010101 010128.211.171.010101011128.211.172.010101100128.211.173.010101101128.211.174.010101110128.211.175.010101111

128.211.168.0/22

128.211.172.0/23/24/24

**1024 addresses128.211.168.0/22512 addresses128.211.172.0/23256 addresses128.211.174.0/24256 addresses128.211.175.0/24The smaller ISP could further partition 128.211.175.0/24Smaller ISP has been allocated 128.211.168.0/21 Can allocate partitions to customers:

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

**9.19 A Classless Addressing Example - continuedClassless 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.

**9.21 Longest-Match and Mixtures of Route TypesConsider the smaller ISPs routers entry router is R0From 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 R2Fwd to R1Fwd to R2 3rd octet4th octet

128.211.168.01010100000000000 128.211.169.010101 001 128.211.170.010101 010 128.211.171.010101011 128.211.172.010101100 128.211.173.010101101 128.211.174.010101110

128.211.175.010101111

**1024 addresses128.211.168.0/22512 addresses128.211.172.0/23256 addresses128.211.174.0/24256 addresses128.211.175.0/249.19 A Classless Addressing Example continued Smaller ISP has been allocated 128.211.168.0/21R2

** 3rd octet R0 table entry

128.211.168.010101000128.211.169.010101 001128.211.170.010101 010128.211.171.010101011128.211.172.010101100128.211.173.010101101128.211.174.0101011109.21 Longest-Match and Mixtures of Route Types continued128.211.175.010101111128.211.168.0/21 to R1128.211.175.0/24 to R2Nothing gets forwarded to R2

**9.21 Longest-Match and Mixtures of Route Types continuedFigure 9.14All traffic will be sent to 10.0.0.2

**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 tableCan help by putting the most specific routes first.

**9.22 CIDR Blocks Reserved for Private NetworksFigure 9.15

*

*Regional Internet RegistriesIP Address Allocation: Internet Assigned Numbers Authorityowns the entire IPv4 and IPv6 address space!

*Allocation of IP addresses (IPv4 and IPv6)mentioned briefly in Comers chapter 4ARINLarge ISPLarge end-user or small ISP

**Exhaustion of IPv4 Address SpaceFebruary 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. No more new blocks of IPv4 addresses!

*Advent of IPv6: World IPv6 Day, 2011On 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.

**31.6 Features of IPv6 Larger Addresses (128-bit)

Extended Address Hierarchy Flexible Header Format Improved Options Not backward compatible with IPv4! Operate Dual stacksChapter 31 - A Next Generation IP (IPv6)

**Recall IPv4 Datagram Header Format

**31.7 General Form of an IPv6 Datagram

**46

**31.8 IPv6 Base Header FormatChanges 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

**31.10 Parsing an IPv6 Datagram Simple case:Hop-by-hop headers precede end-to-end headers.

If source routing specified:If Payload Authentication also specified:

**31.11 IPv6 Fragmentation and Reassembly omit31.12 Consequences of End-to-End Fragmentation - omit31.13 IPv6 Source Routing - omit

31.14 IPv6 Options - omit

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

**31.16 IPv6 Colon Hexadecimal NotationConsider 128-bit address in dotted-decimal form: 104.230.140.100.255.255.255.255.0.0.17.128.150.10.255.255Same 128-bit address in colon-hexadecimal form: 8 groups of 16 bits68E6:8C64:FFFF:FFFF:0:1180:96A:FFFFCompression:FF05:0:0:0:0:0:0:B3written as FF05::B3(left-align what is to left of :: right-align what is to right)CIDR-like:12AB::CD30:0:0:0:0 /60means high-order 60 bits of address are (hexadecimal) 12AB00000000CD3In binary starts with 0110 1000 . 1110 0110 . 1000 1100 . 0110 0100 . 1111 1111 . 1111 1111 . . .

**31.17 Three Basic IPv6 Address Types 31.18 Duality of Broadcast and Multicast omit

31.19 Engineering Choice and Simulated Broadcast - omit 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 Unicast

**31.20 Proposed IPv6 Address Space Assignment

**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

**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)0:0:0:0:0:0:0:1is the loopback address (like 127.0.0.0 in IPv4)

**31.23 Unicast Address StructureThis will be a replacement for Comers treatmentThe 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:ARINLarge ISPLarge end-user or small ISP Internet Assigned Numbers Authority

**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.

**3 bits61 bits 0 0 1 managed by IANA 3 20 41 Allocated by IANA0 0 1 to ARIN managed by ARIN 3 20 9 32 Allocated by IANA Allocated by0 0 1 to ARINARIN to large ISP managed by large ISP 3 20 916 16 Allocated by IANA Allocated by Assigned by ISP managed by0 0 1 to ARINARIN to large ISP to large end-site end-siteAssignment of IPv6 unicast addresses/3/23/32/48

** 3 20 916 16 Allocated by IANA Allocated by Assigned by ISP managed by0 0 1 to ARINARIN to large ISP to large end-site end-site 3 20 9 24 8 Allocated by IANA Allocated by Assigned by ISP mgd. by0 0 1 to ARINARIN to large ISP to small end-site end-site 3 20 9 32 Allocated by IANA Allocated by Assigned by ISP 0 0 1 to ARINARIN to large ISP to end-user /48/56/64

**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 ARINA-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.

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

**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 (manufacturers extension)Fig 31.11This is used in IPv6 Link-Local AddressesF F F E

**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 10If the following 6 bits are zero, this would be hexadecimal FE80The low-order 64 bits encode the interfaces hardware addressExample from network lab machine F1:Ethernet address: 00:B0:D0:63:5B:92Link-local address: FE80::2B0:D0FF:FE63:5B92No need for ARP in IPv6!

**Ethernet address: 00:B0:D0:63:5B:92Link-local address: FE:80::2B0:D0FF:FE63:5B9200000010 F F F E 6 3 5 B 9 2B 0 D 0 0 2So the complete IPv6 address of eth1 on F1 is FE:80::2B0:D0FF:FE63:5B92

**31.26 Autoconfiguration and Renumbering -omitEND OF COURSEMATERIAL!!!

**Exam #3Will be held on Tuesday, May 8 From 9:30 to 10:30amCS 534 term papers due then