Internet Protocol (IP)

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Internet Protocol (IP)

• Basic Functions
• Connectionless Protocol
• Packet Encapsulation

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Basic Functions of IP

• Provide for
• data transfer
• packet addressing
• packet routing
• fragmentation
• detection of packet errors

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Packet encapsulation
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IP Packet

• Version This field contains the IP version
  number, IPv4 or IPv6
• IP header length (IHL) The IP header has a
  minimum size of 20 bytes, but the size can vary
  depending on the size of the Options field.
• Type of service (TOS) This field indicates the
  precedence or priority given to the packet
  contents. It enables routing protocols to
  determine the type of path along which to send a
  packet.
• Length The entire IP packet size, which can be
  up to 65,535 bytes, is provided in this field

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IP Packet

• Identification IP can convert packets from one
  size to another for dissimilar networks
• For example, an Ethernet packet may be 64 to 1518
  bytes in length, while a Fiber Distributed Data
  Interface (FDDI) packet can be up to 4472 bytes,
  and a 16-Mbps token ring packet can be as long as
  17,800 bytes
• IP is able to transfer packets to different types
  of networks by fragmenting the packets
• divide one FDDI packet into fragments to match
  the 1518-byte maximum on an Ethernet network
• When IP fragments a packet, it assigns a single
  group number for all of the fragments and places
  that number in the identification field to ensure
  that fragments are not reconstructed from the
  wrong pieces.
• Flags Flags are used with fragmentation (1) to
  convey information and (2) to show when the last
  fragment in a sequence has been sent (when a
  packet is fragmented).

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IP Packet

• Fragment offset The fragment offset provides
  information about how to reconnect fragments
  within a single fragment group.
• Time to live (TTL) This field contains
  information that prevents a packet from
  continuously circulating around a network.
• Each time an IP packet goes through a router,
  that router reduces the TTL value by a default
  amount determined by the router or set by a
  network administrator
• It is checked by each router through which it
  passes, so that the packet is discarded when TTL
  equals 0.
• Protocol This field is used to show which
  protocol-TCP or UDP-is encapsulated in IP
• Checksum The checksum is a 16-bit cyclic
  redundancy check that is the sum of all values
  contained in every field in the IP header.

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IP Packet

• Source address This is the network address and
  the address of the device that sent the packet
• Destination address This field contains the
  network address and the address of the receiving
  device
• Options There are several options that can be
  used with IP For example, the time when the
  packet is created can be entered, and specialized
  security can be implemented for military and
  government implementations
• Padding Padding fills the options area when
  there is not enough data to complete the
  allocated area, because the total size (in bits)
  of the IP header must be divisible by 32.