3 TCPIP

1
3 TCP/IP

• Many Names
• Internet Protocols
• DOD Protocols
• TCP/IP Protocols

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Why TCP/IP?

• Universally Available
• Open Standards
• Public Domain
• Useful reference to understand other
  protocols
• De facto standard
• Router uses it as a configuration tool
• Telnet for remote configuration
• TFTP to transfer configuration files and OS
  images
• SNMP for network management

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TCP/IP Protocol Suite or Stack

• Not just Transmission Control Protocol and
  Internet Protocol, but contains many other
  protocols.
• Equally well suited for LAN and WAN

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OSI and TCP/IP Layer Correspondence

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Application Layer Overview

• File Transfer
• TFTP, FTP, NFS
• E-mail SMTP
• Remote Login Telnet, rlogin
• Network Management SNMP
• Name Management DNS

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Transport Layer

• Transport Layer
• Flow Control is provided by sliding windows
• Reliability provided by sequence numbers and
  acknowledgements
• TCP and UDP

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TCP

• Connection-oriented, reliable protocol
• Acknowledges receipt of segments
• Breaks messages into segments, and reassembles
  them at destination.
• Resends anything that is not received.
• Provides virtual circuits between end-user
  applications

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UDP

• Connectionless
• Unacknowledged
• Fast and efficient
• Does not breakup data like TCP.
• Reliability delegated to lower layer protocols
  or applications.
• Typically for small amount of data at one time.

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Port or Socket Numbers

• TCP and UDP use port numbers to pass
  information to upper layers.
• Port numbers are used to keep track of different
  conversations crossing the network at the same
  time.
• Port lt 256 for public applications
• 256 1023 assigned to saleable applications
• 1024 and above dynamically assigned by host
  applications

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Well Known Port Numbers

• FTP data
• FTP Control
• Telnet
• SMTP
• DNS
• TFTP
• 80 HTTP
• 161 SNMP
• Will meet them again in Access Lists for security

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TCP Services 3Way Handshake

• TCP Connection Establishment 3 Way Handshake
• Host A initiates connection by sending a packet
  with initial sequence X and SYN bit set to
  indicate a connection request. Host B receives
  the SYN, acknowledging SYN with ACKX1. It also
  sends its own initial sequence number Y.

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TCP Services 3Way Handshake
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TCP Services PAR

• Positive Acknowledgement and Retransmission
  Source sends one Packet, starts a timer, and
  waits for an acknowledgement before sending a new
  packet. If acknowledgement is not received before
  timer expires, the source retransmits the packet.
  
• It is inefficient! Why?

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TCP Services Sliding Window

• Windowing improves flow control and reliability.
  
• Receiving TCP reports a window to the sending
  TCP. The window specifies the number of bytes,
  starting with the acknowledgement number, that
  the receiving TCP is prepared to receive.
• Window sizes are variable during a connection.

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Windowing

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TCP and Segment Formats

• Page 108 Notice the amount of overhead.
• Data begins at byte 20 or at 24
• Page 111 UDP Segment format.
• Data begins at byte 8.
• TFTP, SNMP, NFS, DNS use UDP.

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Internet Layer Protocols

• Corresponds to Network layer of OSI
• Included here are
• IP, ICMP, ARP, RARP and Routing Protocols
• IP Connectionless, best-effort delivery of
  packets and fragmentation and reassembly of
• ICMP Provides messaging and control
  capabilities.

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IP Packet Format

• Page 108 Data begins at byte 20 or 24
• Note
• Fragment offset position of the fragments data
  relative to the beginning of the data in the
  original datagram.
• TTL Prevents endless loops. Counter is
  decremented. If reaches 0, the packet is dropped.

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ICMP Testing

• ICMP messages are carried in IP datagrams and use
  many types of messages.
• Destination unreachable
• Parameter Problem Faulty packets
• Source Quench Flow control
• Redirect Route change
• Echo Test reachability
• Echo Reply Test reachability

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Use of ICMP

• Ping uses ICMP protocol to verify the hardware
  connection and the logical address of the network
  layer. If ping is successful no problems upto
  network layer.
• Trace Uses TTL values to generate messages from
  each router used along the path. Can locate
  problems along the path from source to
  destination.

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• Telnet tests all 7 layers of OSI model. If
  successful, communication is ok.
• Need not memorize TCP, UDP, and IP header
  formats.

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IP Addressing

• Classful Addresses
• Class A
• Class B
• Class C

Network 1Byte
Host 3 Bytes
Network 2 bytes
Host 2 bytes
Network 3 bytes
Host 1 byte
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First Octet Rule

• Can find of the class of the network from the
  first byte.
• Class A 0XXXXXXX
• First bye range 1 to 126. 127 is reserved
• Class B 10XXXXXX
• First byte range 128 - 191
• Class C 110XXXXXX
• First byte range 192 - 223

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IP Address Classes

• Class A 1 to 126
• Class B 128-191
• Class C 192-223
• Class D 224-239 Reserved Multicast
• Class E 240-255 Reserved Experimental

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Special IP Addresses

• LoopBack 127.0.0.0 is reserved for the
  loopback. It is used by a device to address
  itself internally. This technique is used to test
  the local devices TCP/IP stack and identify
  possible stack corruption.
• Unsuccessful ping 127.0.0.1 indicates TCP/IP
  installation and configuration problems.
• 10.X.X.X are reserved for internal use.

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Addressing without Subnets

• Class A networks can have 256X256X256 hosts
  16.7 million hosts.
• Class B networks can have 256 X 256 65 thousand
  hosts.
• What if we arrange all the 1.677 million
  computers as one network?
• Good Small routing tables.
• Bad Broadcast Storms

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Broadcast Domain, Storms

• Broadcast domain is the set of all devices that
  will receive broadcast frames originating from
  any device within the set.
• Broadcast Storm many broadcasts are sent
  simultaneously across all network segments. A
  broadcast storm uses substantial network
  bandwidth and results in poor performance.

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A Solution

• Subnetting Network use is more efficient.
  Outside world sees the network as one network but
  inside there is more structure.
• If 172.16.0.0 (class B) is divided into
  172.16.1.0, 172.16.2.0, 172.16.3.0, and
  172.16.3.0, routers determine the destination
  network using the subnet address.

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Example

• 172.16.1.0
  172.16.2.0
• 172.16.4.0
  172.16.3.0
• Receives all 172.16.x.x traffic

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How data moves on the network

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• 1.2 attaches network header to data. DA 3.4, SA
  1.2.
• 1.2 sends packet over token ring to default
  router 1.5.
• Router accepts and ACKs the packet.
• Router examines destination network number (3),
  looks in routing tables for best path, drops
  token ring envelope and builds a WAN envelope,
  then sends packet over WAN.
• Packet is sent from router to router via best
  path according to routing tables, based on
  destination network number.
• Router 3.5 recognizes DA as its own, drops WAN
  envelope and builds Ethernet envelope, and places
  packet on LAN.
• 3.4 recognizes the DA as its own, drops the
  Ethernet frame, and forwards the data to upper
  layers.

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Subnet Mask

• By default, first 16 bits of the IP address of
  Class B network is network address.
• Subnet Mask modifies the number of network bits
  and host bits.
• By using subnet mask, a device finds out what
  part of IP address is used for network address,
  the subnet and and the host address.

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Subnetting

• Subnetting Stealing a part of the host
  addresses and using them for network address.
• 172.16.0.0 is a class B network.
• Can have 65K hosts. Suppose the company wants to
  make 6 subnets.

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of bits needed for subnets

• How many bits do we need to steal from host
  address.
• 1 bit 0 or 1 2 subnets
• 2 bits 00 01 10 11 4 subnets
• 3 bits 000 - 111 8 subnets
• Need 3 bits to create 6 subnets

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Subnet Mask

• Subnet Mask Tells how many bits are used for
  network address and how many for host addresses.
• 1 indicates used for network address
• 0 not used for host address
• Took 3 bits from host address.

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Subnetting

• 11111111.11111111.11100000.00000000
• 255.255.224.0 is the subnet mask.
• Max. hosts on any of these subnets
• 13 bits for indicating hosts.
• 213 8192 hosts.
• Rather than 65 k hosts on one network, 8 hosts on
  8 subnetworks.

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Subnet Mask

• Express subnet mask as
• 11111111.11111111.11100000.00000000 or
• 255.255.224.0 is a lot of numbers. Extended
  prefix notation /19
• 19 bits of subnet mask. Leading bits are 1s
  followed by 0s

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The Subnets

• 172.16.000xxxxx.xxxxxxxx
• 172.16.001xxxxx.xxxxxxxx
• 172.16.010xxxxx.xxxxxxxx
• 172.16.011xxxxx.xxxxxxxx
• 172.16.100xxxxx.xxxxxxxx
• 172.16.101xxxxx.xxxxxxxx
• 172.16.110xxxxx.xxxxxxxx
• 172.16.111xxxxx.xxxxxxxx

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Confusion

• In the old days, all 0s and all 1s subnets
  could not be used. That is, first and last
  subnets in previous slide cannot be used as
  subnets. But modern routing protocols allow the
  use of those subnets now.
• In Lammle you are asked to use middle six subnets
  only.
• In 3Com paper you are told to use all 8.

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Further Practice

• You may also want to look at
• http//www.learntosubnet.com
• For further examples of subnetting.
• There you will find excellent notes on how
  Internet works and how DNS works.

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Reserved Addresses

• Subnet Address To refer to the subnet itself,
  put 0s in host address field.
• Subnets 172.16.0.0, 172.16.32.0,
• 172.16.64.0, 172.16.96.0,
• 172.16.128.0, 172.16.160.0,
• 172.16.192.0, 172.16.224.0.
• Remember to count from 0!

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Broadcast Address

• Broadcast To send to every computer on the
  network.
• Broadcast address all 1s in host address bits.

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Broadcast Addresses

• Subnet Broadcast Address
• 172.16.0.0 172.16.31.255
• 172.16.32.0 172.16.63.255
• 172.16.64.0 172.16.95.255
• 172.16.96.0 172.16.127.255
• 172.16.128.0 172.16.159.255
• 172.16.160.0 172.16.191.255
• 172.16.192.0 172.16.223.255
• 172.16.224.0 172.16.255.255

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Problem

• Have 132.45.0.0/16 network
• 1 How many bits for 8 subnets?
• 2 Extended prefix to create 8
• subnets?
• 3 Express the subnets in binary
• and dotted decimal formats
• 4 Range of host addresses to
• assign to subnet 3
• 5 What is is broadcast address of
• subnet 3?