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 • User’s 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. DSAP Record DSAP Record 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 LAN’s • 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 Router 4 3 3 3 2 2 2 2 • A router operates at layer 3 of OSI model 1 1 1 1 Subnetwork Subnetwork

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

18. 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 • Good way to accommodate OSI and non OSI protocols • Gateways use all seven layers of the OSI stack 1 1 Subnetwork Subnetwork

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 Network access Datalink Physical TCP/IP protocol suite OSI

24. Communication Using the TCP/IP End system End system App App TCP TCP IP IP Router NAP2 NAP1 IP Subnet2 Subnet 1 NAP 2 NAP 1

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

26. 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.

27. 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)

28. 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

34. 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

41. 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.