Internetworking

1
Internetworking
Organizational Communications and
Technologies Prithvi Rao
H. John Heinz III School of Public
Policy and Management Carnegie Mellon
University
2
Objectives

• To investigate use of bridges and routers
• Define an internetwork
• Recognize the importance of internetworking
• List examples of relevant internetworking
  equiopment
• Relate equipment back to protocols they use and
  the OSI layer in which they reside

3
Readings
Chapters 14 and 15 Business Data Communications
William Stallings and Richard Van Slyke
4
Internetworking

• Distributed organizations
• distributed set of networks
• LAN islands
• cross functional work
• teams across traditional org. boundaries
• Any interconnected set of diverse or homogeneous
  networks is called an INTERNET.
• Each constituent network referred to as a
  Subnetwork or Subnet.

5
The Role of Architectures

• Users perception is that there is a single
  network
• Devices that make this possible are repeaters,
  bridges, routers, and gateways
• Internetworking requires an understanding of
  architectures and their associated protocols

6
Architectures Some Examples

• OSI
• TCP/IP
• SNA
• DNA

7
Recall the OSI Architecture
Application
Users of transport service
Presentation
Session
Users liaison
Transport
Network
Network service
Data link
Physical
8
A Simplified Architecture for File Transfer
Computer 2
Files and file transfer commands
File transfer application
File transfer application
Communications-related messages
Communications service module
Communications service module
Network interface logic
Network access module
Network access module
Communications network
Computer 1
9
Communications Architectures and Networks
Processes 1 2 ( ) ( ) Transport
Service access point address
Processes 1 2 3 ( )-( )-( ) Transport
Communication network
Network access
Network access
Host C
Host B
10
Peer to Peer CommunicationsArchitecture
Application
Application
Record
Record
A-send (Dest. host Dest. SAP Record)
TPDU
TPDU
Transport
Transport
T-Send(DESt. Add, PDU)
Packet
Network access
Network access
DHost
DSAP
Record
Computer X
Computer Y
11
Internetworking devices

• Repeaters
• at the physical layer
• Bridges
• at the MAC layer
• Routers
• at the network layer
• Gateways
• at the network or higher layer

12
Repeater

• Allows multiple LAN segments to be interconnected
  at the physical layer. Extends physical coverage.

7
7
6
6
5
5
4
4
End system
End system
Repeater
3
3
2
2
1
1
1
Subnetwork
Subnetwork
13
Bridges

• A device that operates at Layer 2 of the OSI
  stack used to segment LANs
• Acts as an address filter
• maps MAC layer addresses to segments
• picks up packets on one LAN addressed to a
  destination on another LAN and passes those
  packets on.
• Variants on this theme exist in the marketplace
  (e.g., brouters)

14
Bridge
End system
End system
7
7
6
6
5
5
4
4
Bridge
3
3
2
2
2
1
1
1
1
Subnetwork
Subnetwork
15
Routers

• Devices that operate at Layer 3 of OSI Stack
• Used to connect networks that may or may not be
  similar
• Routers are a key component of enterprise
  networks and the Internet

16
Router
End system
End system
7
7
6
6
5
5
4
4
Router
3
3
3
2
2
2
2
1
1
1
1
Subnetwork
Subnetwork

• A router operates at layer 3 of OSI model

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Router Operation
Host X
Host Y
Router 1
Router 2
TCP
TCP
IP
IP
IP
IP
LLC
LLC
X.25-3
LLC
LLC
X.25-3
MAC
X.25-2
MAC
MAC
MAC
X.25-2
Physical
Physical
X.25-1
Physical
Physical
X.25-1
LAN B Token Ring
LAN A Ethernet
WAN C X.25 Subnet
a
a
b
c
d
d
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Router Capabilities

• Addressing schemes
• differences between LAN addressing schemes and
  X.25 schemes
• Maximum packet sizes
• Ethernet maximum is 1500 bytes while X.25 maximum
  is 1000 bytes
• Interfaces
• implement interfaces to the networks over which
  data is routed

19
Gateways
End system
End system
Gateway application
7
7
6
6
5
5
4
4
3
3
2
2
1
1
Subnetwork
Subnetwork

• Good way to accommodate OSI and non OSI protocols
• Gateways use all seven layers of the OSI stack

20
Interconnecting diverse networks

• Suppose there are N protocols to interconnect
• Option 1 Have N(N-1) mappings
• Option 2 Have one common protocol. Now we
  require 2N mappings
• IP uses this approach.

21
TCP/IP

• Core of the Internet DOD developed
• Popular, mature protocol stack with large, market
  share
• The DoD approach stems from extensive
  experimentation with the ARPANET.
• ARPANET started in the late 1960s', and has grown
  to hundreds of nodes today.

22
TCP/IP

• Fundamental Principle of the DoD architecture
• Communication between local and remote processes
  is achieved by first identifying the remote host
  and then locating the remote process within the
  remote host.
• The network now needs to route data between
  hosts, without bothering about the remote
  process.
• Hierarchical layering, with four layers
  Application, Transport, Internet, and Network.
• Higher layers may bypass adjacent layers and
  directly access a lower layer (Efficient!)

23
A Comparison of the OSI and TCP/IP Communications
Architectures
Application
Process
Presentation
Session
Host-to-host
Transport
Internet
Network
Data link
Network access
Physical
TCP/IP protocol suite
OSI
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Communication Using the TCP/IP
End system
End system
App
App
TCP
TCP
IP
IP
Router
NAP2
NAP1
IP
Subnet2
Subnet 1
NAP 1
NAP 2
25
Protocol Data Units in TCP/IP
Application byte stream
User data
TCP segment
TCP header
IP datagram
IP header
Network-level packet
Network header
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IP Basics

• Connectionless Datagram Network Protocol.
• Designed with Internetworking in mind.
• Core IP Functions
• Support Fragmentation and Reassembly
• Routing
• Error Reporting
• Error checking covers only the IP header.

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IP Helper Protocols

• Internet Control Management Protocol (ICMP)
• Address Resolution Protocol (ARP)
• Domain Name Service (DNS)
• Routing Protocols
• Interior R(outing)IP, OSPF (Open Shortest Path
  First)
• Exterior BGP (Border Gateway Protocol)

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IP Addressing

• Hierarchical addressing scheme for scalability.
• Logic for addressing scheme
• Class based addressing
• There would be a few very large networks (class
  A).
• There would be a large number of small networks
  (class C).
• 32-bit addresses
• Network and host parts
• Length of network and host parts depends on the
  class of network.

29
IP Addressing

• Dotted decimal notation
• 128.102.16.10 (NS.NSAS.GOV)
• Class B addresses. Start with 10
• NS.NASA.GOV has a globally unique address
  128.102.16.10
• netid is 128.102, assigned by Network Information
  Center (NIC)
• subnetid is 16, assigned by NASA (in this case)
• hostid is 10, assigned by NASA Lab(I n this case)
• Broadcast Address Hostid is all 1's.

30
IP Routing

• Classless Inter-Domain Routing (CIDR)
• introduced in the early 90s
• to improve address space usage
• IPv6 Changes
• 128-bit address length
• class less routing
• hooks for QoS

31
Location of hosts on the Internet

• How do hosts find each other on the internet?
• Need Physical Address.
• Relationship between Physical Addresses and IP
  Addresses.
• Ethernet addresses are 48-bits.
• IP addresses are 32-bits. Address Mapping is done
  by the network.
• Each machine has an associated (IP,NPA) address
  pair.
• Broadcast Address Resolution Packet using the
  Address Resolution Protocol (ARP)

32
Controlling the Internet

• Internet Control Message Protocol (ICMP)
• ICMP Functions
• Communicate errors back to host destination
  unreachable, datagram errors, excessively long
  routes detected, other failures.
• Testing destination reachability and status.
• Datagram flow control.
• Route change requests (redirect).
• Obtain information such as NPA and subnet mask.

33
Transport Layer Functions

• Provides an interface between higher layers and
  the underlying network.
• End-to-End Reliable Connectivity between hosts.
• Connectivity is between ports on hosts.
• The port addresses are only locally unique.
• In TCP, some standard ports are defined for
  telnet, ftp, mail.
• End-to-end error checking may be provided.
• Common transport protocols
• User Datagram Protocol (UDP)
• Transmission Control Protocol (TCP)
• ISO Transport Protocol

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User Datagram Protocol

• Connectionless datagram protocol with low
  overhead
• Limited error checking or recovery. Assumes a
  reliable network layer.
• UDP checksum is optional and need not be used.
• Used commonly on LANs. UDP is used with SUN's
  network file system (NFS).
• Port Number Transport Service Access Point
  (TSAP) in OSI

35
Transport Control Protocol

• Reliable Transport Protocol
• Assumes very little about the underlying network,
  and can be used with a variety of networks.
• Dial-up telephone lines
• Internet IP datagram service
• LANs
• High speed fiber optics network
• Low speed long haul network
• Wireless links

36
TCP Features

• TCP is Connection-oriented.
• TCP provides end-to-end error checking.
• TCP provides end-to-end flow control (sliding
  window flow control).
• Full duplex connection.
• Higher overhead.

37
Internet Administrative Bodies

• Internet Society (ISOC)
• non-governmental international society
• Technology management
• standards, RFC process
• Internet Architecture Board (IAB www.iab.org)
• Internet Engineering Steering Group (IESG)
• Internet Engineering Task Force (IETF
  www.ietf.org)
• Internet Assigned Number Authority (IANA
  www.iana.org)
• RFC Editor
• InterNIC
• domain name registry and IP network number
  assignment

38
Internet Administrative Bodies

• Internet Corporation for Assigned Names and
  Numbers (ICANN)
• non-govermental group
• Responsible for assigning names and numbers for
  the Domain Name System (DNS)
• Arose in an environment of controversy

39
Internet Services

• TCP/IP based application layer protocols
• SMTP (email)
• HTTP (WWW)
• SNMP (network management)
• FTP (file transfer)
• telnet (terminal emulation)
• Ubiquity of this standards compliant platform has
  profound implications
• intra-organizational systems
• intranets
• inter-organizational systems
• business to business commerce, business to
  consumer

40
Internet-enabled Applications

• Pull technology
• www, ftp
• Push Technology
• Pointcast

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Using the WWW to increase reach

• Customer access to internal systems
• tracking of packages
• fedex, ups,...
• Mutual fund information
• vanguard, fidelity
• Frequent flier miles
• American, Delta

42
Electronic Marketplaces

• Amazon
• bookstore on the web
• over 1 million titles
• low prices
• Export Administration Regulations
• developed and administered by NTIS
• 21/month for access to regulation database

43
Push technologies

• Pointcast
• information bundled with advertising
• brings newspapers, CNN etc. as per user interests
  to the desktop
• can be used as a screen saver
• updates itself on predetermined schedule or on
  demand
• available at www.pointcast.com

44
Summary

• Internetwork is a network of networks which must
  be capable of connecting networks together.
• Internetwork consists of a number of computer
  platforms, operating systems and network
  interfaces. Goal of open internetworking is to
  overcome these differences.
• Repeaters, bridges, routers and gateways required
  for accomplishing communication outside single
  LAN.