Internet Protocol

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Internet Protocol
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Layered Network

• Why layered network architectures?
• To help manage complexity
• To facilitate the building block approach to
  implementation management

• How many layers are enough?
• Depends on who's counting.
• ISO/OSI model said 7 (or so)
• Internet model says 5 (or so)
• There is no correct answer.

International Organization for Standardization
(ISO) Open System Interconnect (OSI)
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OSI Model

• Application
• Presentation
• Session
• Transport
• Network
• Data link
• Physical

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Internet Model

• Application
• Transport
• Network
• Link
• Physical

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Simplified OSI and TCP/IP Models
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Five Layer Software Schematic
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Protocol Encapsulation
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The Internet Network layer

• Three major components IP protocol, Routing
  protocols, ICMP protocol

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IP Addressing

• Internet addresses specify a host's connection(s)
  to a network.
• A host may have more than one IP address - to the
  same or to multiple networks.
• Internet addresses are 32 bits long and have four
  different forms classes A, B, C and D.
• Addresses include both a network ID and a host
  address.
• IP addresses are written with dotted decimal
  notation (for example, 140.114.63.1)
• Internet routing is based on network ID.
• Internet addresses must be mapped to physical
  network addresses (for example, by the Address
  Resolution Protocol on LANs).

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IP Address, Structure

• Two levels network ID and host ID
• Network Classes
• Class A 7-bit net ID, 24-bit host ID
• Class B 14-bit net ID, 16-bit host ID
• Class C 21 bit net ID, 8-bit host ID
• Class D 28-bit group ID for multicast services
• Class E reserved

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IP Addresses - Class A

• Start with binary 0
• All 0 reserved
• 01111111 (127) reserved for loopback
• Range 1.x.x.x to 126.x.x.x
• 27 -2 126 class A network addresses

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IP Addresses - Class B

• Start with binary 10
• Range 128.x.x.x to 191.x.x.x
• Second Octet also included in network address
• 214 16,384 class B network addresses

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IP Addresses - Class C

• Start with binary 110
• Range 192.x.x.x to 223.x.x.x
• Second and third octet also part of network
  address
• 221 2,097,152 network addresses

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IP Addresses - Class D and E

• Class D 28-bit group ID for multicast services
• Class E reserved

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Special IP Addresses

• 0.0.0.0 this host on this net
• 0.0.0.hostid specified host on this net
• 127.0.0.1 loopback address
• 255.255.255.255 limited broadcast, this subnet
• ...255 net directed broadcast
• The value 0 typically means this host or this
  net.

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Subnet Addressing

• Original IP address space not optimized for large
  numbers of small networks
• Subnetting allows a single network to be split
  into multiple networks for internal use but
  appear as a single network to the outside world
• Subnets require subnet masks to separate
  networks from hosts

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Subnet mask

• Indication of (net ID subnet ID) with binary
  1s
• The portion of host ID contains all 0s
• Example - 11111111 11111111 11111111 00000000
  (255.255.255.0)
• Notation of IP address (IP address/subnet mask)
• 140.114.79.132/255.255.255.0

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Operations of subnet mask

• Network_address (net ID subnet ID)
  (IP_address AND MASK)
• For example
• 140.114.79.132 AND 255.255.255.0
  140.114.79.0
• Host_ID IP_address AND (NOT MASK)
• For example
• 140.114.79.132 AND (NOT 255.255.255.0)
  0.0.0.132

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CIDR -- Classless InterDomain Routing

• CIDR was invented to keep the internet from
  running out of IP addresses
• documented in RFC1519 (1993)
• CIDR uses variable length subnet masks (VLSM) to
  allocate IP addresses to subnets according to
  individual need
• subnet portion of address of arbitrary length
• address format a.b.c.d/x, where x is bits in
  subnet portion of address (Example,
  140.114.79.132/24)

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IP addresses how to get one?
Q How does network get network part of IP
address? A gets allocated portion of its
provider ISPs address space
ISP's block 11001000 00010111 00010000
00000000 200.23.16.0/20 Organization 0
11001000 00010111 00010000 00000000
200.23.16.0/23 Organization 1 11001000
00010111 00010010 00000000 200.23.18.0/23
Organization 2 11001000 00010111 00010100
00000000 200.23.20.0/23 ...
..
. . Organization 7
11001000 00010111 00011110 00000000
200.23.30.0/23
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IP addresses how to get one? (Cont.)

• Q How does an ISP get block of addresses?
• A ICANN Internet Corporation for Assigned
• Names and Numbers
• allocates addresses
• manages DNS
• assigns domain names, resolves domain name
  disputes

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IP addresses how to get one? (Cont.)

• Q How does host get IP address?
• Manual configuration
• hard-coded by system administrator in a file
• Win control-panel-gtnetwork-gtconfiguration-gttcp/ip
  -gtproperties
• UNIX /etc/rc.config
• DHCP Dynamic Host Configuration Protocol
  dynamically get address from a server
• plug-and-play

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The format of the IP header
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Version Number

• The version number of IP V4 (Version 4)

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Internet Header Length (IHL)

• IHL is the header length in 32-bit words (4
  bytes)
• Minimum header length is 5 (i.e., 5 ? 32 bits)
• All the IP header fields except options and
  padding are mandatory
• IHL is NOT packet size (only header)

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Type of Service

• Specify
• (1) Desired reliability
• (2) Desired priority
• (3) Desired end-to-end delay
• (4) Desired throughput
• Usually set to 0 (not used)

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Total Length (16 bits)

• Total packet length in bytes
• The packet length, including IP header and user
  data field

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IP Fragmentation Reassembly

• network links have MTU (max.transfer size) -
  largest possible link-level frame.
• The links on a route can use different link
  types, different link-layer protocols, and
  different MTUs
• large IP datagram are divided (fragmented)
  within network
• one packet becomes several packets
• reassembled only at final destination
• IP header bits used to identify, order related
  fragments

fragmentation in one large packet out 3
smaller packets
reassembly
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Identification (16bits)

• This field is needed in case fragmentation is
  needed.
• Created by sender, all smaller packets have the
  same identification number as the original packet

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Flags (3 bits)
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Fragment Offset (13 bits)

• Offset of the 1st byte of the fragment from the
  beginning of the original data
• Specified in units of 8-byte chunks

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Example of Flag bits and Fragmentation Offset
field

• 4000 bytes packet, MTU 1500 bytes, IHL5 (20
  bytes of header)

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Time-To-Live (TTL) (8 bits)

• Number of hops /links that the packet may be
  routed
• The hop counter will be decreased by one at every
  intermediate router
• If TTL 0, a router drops the IP packet

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Time-To-Live (TTL) (continued)

• traceroute utility
• Source sends series of UDP segments to
  destination
• First has TTL 1
• Second has TTL2, etc.
• Unlikely port number

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High Level Protocol (8 bits)

• To which higher protocol
• should IP deliver this packet
• Examples 1 ICMP 2 IGMP
• 6 TCP 17 UDP

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Header Checksum (16 bits)

• CRC Check Sum code only for the IP header

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Source/Destination IP addresses (32 bits each)

• To identify who is the sender and the destination