The IP Addressing Scheme

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The IP Addressing Scheme
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Addressing

• We examine the addressing scheme specified in the
  Internet Protocol layer of the TCP/IP model
• Critical to internets
• Each device must have unique address
• Give appearance of unified system
• Physical addresses cant be used
• Not necessarily unique
• Not just one kind of hardware
• IP address independent of hardware

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Addressing Continued

• Illusion of single, large network
• Hides various physical details
• IP has unique 32-bit addresses for each host
• Divided into two parts
• Prefix Network number
• Suffix Host number, on a particular network

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IP Addresses

• No two networks have same number (prefix)
• No two hosts on a network have same number
  (suffix)
• IP has two-level hierarchical routing
• Network numbers must be coordinated globally
• Host numbers do not need that

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Classes

• As IP addresses divided in to, prefix and suffix
  affect each other
• Small prefix ? few networks with many hosts
• Large prefix ? many networks with few hosts
• IP has classes to create well-sized networks

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Classes Continued

• First bits denote which class an address belongs
  to
• A, B, C are the primary classes
• D is used for multicasting
• Hosts interested in multicast share IP address
• Network numbers given out by Internet Assigned
  Number Authority (IANA)

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Dotted Decimal

• Each octet treated as unsigned binary number

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Prefix Ranges
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Host Counts
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Subnetting

• Originally, IP addressing had only the addressing
  scheme thus far Classful Addressing but it
  has limits and is inflexible
• Prefix/suffix separation only on octet boundaries
• Practice introduced since late 80s to divide
  network address scheme into sub-network address
  scheme
• Instead of having three classes, can further
  subdivide classes and have many (done especially
  with B)
• More granularity for number of hosts
• Network/host boundary no longer on octet boundary
  now on bit boundary
• Nine hosts need only 4 bits

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Subnet Masks

• Classless addressing must specify where
  prefix/suffix division occurs along with address
• Have subnet mask that specifies how many bits are
  in network portion
• 147.153.170.17/255.255.255.0
• 147.153.170.17/24

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Subnet Masks Continued

• Each network must have unique prefix
• Network prefix now not only of 3 types
• Among class C addresses can break the prefix
  195.120.18 into several prefixes and assign
  these
• 195.120.18.16/28
• 195.120.18.32/28
• 195.120.18.64/28
• Etc.
• Effectively breaking down a class C network into
  sub-networks (Can do same for A and B)
• ISP can give out subnets or I can break my big
  network into subnets this way (can map to LAN
  segments this way)

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CIDR (Cider)

• In 1993 IETF began using Classless Inter-domain
  Routing scheme to assign new IP network addresses
• Network assignments not given on A/B/C basis
  rather assign class plus mask, as in
• 190.100.100.0/22
• Network address is actually (in binary 22 bits)
• 10111110 01100100 011001
• Leaves 10 bits for hosts
• Allows 1024 possible network addresses on class B
  network
• Can assign network address 190.100.64.0/22 to
  someone else (some other network) getting
  multiple use out of the prefix 190.100!

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CIDR Masking
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Special Addresses

• Network addresses
• All 0s in host part fill in proper bits for
  network part (based on mask)
• Used for routing
• Directed broadcast
• All 1s in host part
• All machines on a network

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Special Addresses Continued

• Limited broadcast to a given LAN
• All 1s
• All hosts on this network
• This computer
• All 0s
• Sometimes used during boot

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Special Addresses Continued

• Loopback
• 127/8
• Packets dont leave computer, all done in
  software
• Berkeley broadcast different way of doing
  direct broadcast
• All 0s in host
• Really should be network address

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Special Addresses Continued
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Routers and Multi-home Hosts

• Have more than one NIC ? have more than one IP
  address
• Used to route packets
• Typically used as gateway off a LAN
• Typically the .1 address
• Multi-homed for reliability or performance

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Questions

• 18.11
• See homework 6, problems 4, 5.