# IPv4 Addresses. Internet Protocol: Which version? There are currently two versions of the Internet Protocol in use for the Internet IPv4 (IP Version 4)

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• Internet Protocol: Which version? There are currently two versions of the Internet Protocol in use for the Internet IPv4 (IP Version 4) Specified in 1980/81 (RFC 760, 791) Four byte addresses Universally deployed Problem: Address space almost exhausted IPv6 (IP Version 6) Specification from 1998 (RFC 2460) Significant differences to IPv4, but not fundamental changes 16-byte addresses Problem: Not widely used (yet?)
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• Slow adoption of IPv6 IPv6 is available since 15 years, and almost all operating systems now support it But IPv6 is not yet widely adopted Measurements at Internet Exchange Point in Amsterdam: linearsemi-log
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• Slow adoption of IPv6 IPv6 is available since 15 years, and almost all operating systems now support it But IPv6 is not yet widely adopted Measurements at Internet Exchange Point in Amsterdam: linear
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• ECE 461: IPv4 based We use IPv4 throughout in lecture, labs, and assignment IPv6 concepts are discussed in the lecture
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• IP Addresses An IPv4 address is an address of the Internet Protocol Version 4. When the version is understood from the context we only say IP address On the public Internet, an IP address is unique global address of a network interface The IP address is used by hosts and routers for delivery of IP datagrams
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• Dotted Decimal Notation IPv4 addresses are written using dotted decimal notation: Each byte is identified by a decimal number in the range [0..255], separated by periods (`dots). Example: 1100100100000000000101100111100 1 st Byte = 128 2 nd Byte = 100 3 rd Byte = 11 4 th Byte = 60 128.100.11.60
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• IP address consists of a network prefix and a host number Network prefix identifies a particular network Host number identifies an interface on the network The delivery of a packet from a sender to the destination proceeds in 2 steps: 1.Use network prefix to deliver packet to the right network 2.Once the network is found, use the host number to deliver packet to the right interface How can you determine the length of the network prefix? Structure of an IP address network prefixhost number
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• The length of the network prefix must be provided in addition to the numerical value of the address There are two conventions for indicating the length: 1.Add length of the network prefix to address (prefix notation, slash notation, CIDR notation) 2.Add bitmask of the network prefix in dotted decimal notation (netmask) Length of network prefix network prefixhost number 32 bits Length of network prefix
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• Example: Suppose the network prefix is 16 bits long Prefix notation: 128.100.11.60/16 Netmask notation: 128.100.11.60 255.255.0.0 Notation of IP address
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• Special IP Addresses IP address of a network Host number is set to all zeros, e.g., 128.100.0.0 Broadcast address Host number is set to all ones, e.g., 128.100.255.255 Broadcast goes to all hosts on the network The address 255.255.255.255 is a broadcast on the local network Convention for default gateway (but not a reserved address): Default gateway has host number set to 1, e.g., 128.100.0.1
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• Network Prefix and Address Block The IP address of a network has the host number set to 0: 128.100.0.0 Network address with prefix length is called network prefix: 128.100.0.0/16 or 128.100/16 A network prefix is interpreted as a range of IP addresses: 128.100.0.0/16 128.100.0.0128.100.255.255 A network prefix is also called address block It provides the range of addresses allowed on the network The shorter the network prefix, the larger the address block
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• Network prefix length and address block size Network Prefix # of IP Addresses /321 /312 /304 /24256 /23512 /221,024 /212,048 /204,096 /1665,536 /816,777,216 /21,073,741,824 /12,147,483,648 To set up a network of a given size, one needs to acquire a address block with a sufficient number of addresses
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• How does one get an IP network address? Internet Assigned Number Authorities (IANA) manages the global IP address space. IANA allocates addresses to Regional Internet Registries (RIR) IANA allocates addresses in /8 address blocks All available blocks have been allocated. The last available address block was assigned in 2011 IANA End user allocates assigns End user assigns RIR LIR (ISP)
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• How does one get an IP network address? RIR allocates addresses to Local Internet Registries (LIR) LIRs are generally Internet Service Providers Block sizes are /20 or larger End users obtain addresses from an RIR or LIR Some countries have National Internet Registries (NIR), which are between the RIR and LIR levels IANA End user allocates assigns End user assigns RIR LIR (ISP)
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• Regional Internet Registries There are five Regional Internet Registries, each responsible for managing the address space of a large geographic area Address blocks managed by the RIRs are listed at: http://www.iana.org/assignments/ipv4-address-space/ipv4-address-space.xml
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• Available IPv4 addresses (9/2012) RIRs are running low on IP addresses: (one /8 address block 16.8 million IP addresses) Current status of remaining IP addresses: Source: http://www.potaroo.net/tools/ipv4/index.html (2012)Addresses in RIR Pool (/8s) Approximate number of Addresses APNIC0.9138 15 million RIPENCC1.1984 20 million ARIN3.3656 56 million LACNIC3.2246 54 million AFRINIC4.1441 70 million (2013)Addresses in RIR Pool (/8s) Approximate number of Addresses APNIC0.8363 14 million RIPENCC0.8681 14.5 million ARIN1.8219 30 million LACNIC1.9690 33 million AFRINIC3.6389 61 million
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• IPv4 exhaustion and Migration to IPv6 The vast majority of IPv4 addresses are used up IPv4 exhaustion Adoption of IPv6 is driven by IPv4 exhaustion: There have been numerous predictions of imminent IPv4 exhaustion People have been creative with slowing down IPv4 exhaustion through policies and protocols IPv4 exhaustion will occur gradually, but is increasingly urgent As IPv4 addresses become less available, the use of IPv6 is expected to increase substantially The migration from IPv4 to IPv6 is expected to be a slow transition, lasting a decade or more Until then, IPv4 and IPv6 will co-exist
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• Classful IP Addresses When Internet addresses were standardized (early 1980s), the Internet address space was divided up into classes Three classes available for interfaces: Class A: Network prefix is 8 bits long Class B: Network prefix is 16 bits long Class C: Network prefix is 24 bits long Two additional classes: Class D: Used (multicast) group addresses Class E: Reserved for future use
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• Classful IP Addresses The classes were identified by the bit values of the IP address Class A: IP address starts with 0 Class B: IP address starts with 10 Class C: IP address starts with 110 Class D: IP address starts with 1110 Class E: IP address starts with 11110 The length of the network prefix is implied by the address There is no need to provide the length of the network prefix
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• We will learn about multicast addresses later in this course Class E addresses have never been released for use
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• IP Allocation with Classful IP Addresses Limited flexibility for obtaining a network address: Class C: 2 24 - 2 = 254 IP addresses: Class B: 2 16 - 2 = 65534 IP addresses Class A: 2 24 - 2 = 16,772,214 IP addresses Too few network addresses for large networks 2 7 = 128 Class A networks 2 14 = 16,384 Class B networks Flat address space. Routing tables in the backbone Internet need one entry for each network address. Class C networks: up to 2 21 = 2,097,152 entries By 1993, the lookup time of routing tables had become a bottleneck for Internet performance
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• From Classful to Classless In 1993, there was a major shift for interpreting and allocating IP addresses: until 1993: Classful Addresses until 1993: Classful Addresses after 1993: Classless Interdomain Routing (CIDR) after 1993: Classless Interdomain Routing (CIDR)
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• CIDR - Classless Interdomain Routing CIDR abandons the notion of classes Key Concept: The length of the network prefix of IP addresses can be

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