Internet protocols

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  • Have different groups take different questions
  • Movie from 1:22-11:28 is a reasonable lead up to this.
  • Hand out subnet.ID address index cards
  • Dynamic or static IPs on home computers?
  • Hand out index cards with address. (1.0 on stage left 1.6 on stage right) Circulate message inside envelop.
  • Start at 1.2 and send to 5.5; Start at 3.3 and send to 1.5, but have 1.3 send the wrong way (bad update); start at 6.1 to 4.2 HopLimit 10
  • Internet protocols

    1. 1. Internet Protocols Midterm is two weeks away  Break is Saturday 
    2. 2. Review <ul><li>Given a video file with a message latency of 2 minutes, how much faster will a streamed version of the video start to play if each video segment has a message latency of 4 seconds? </li></ul><ul><li>Suppose that a video is divided into 2-second segments for a streaming broadcast </li></ul><ul><ul><li>Does streaming work if each segment has a 1 second transmission time and a 3 second delay? </li></ul></ul><ul><ul><li>Does streaming work if each segment has a 3 second transmission time and a 1 second delay? </li></ul></ul>
    3. 3. Fetching a Web Page www.si.umich.edu Home computer The Internet
    4. 4. Fetching a Web Page www.si.umich.edu Home computer The Internet MichNet Modem
    5. 5. Overview Of Internet Topics <ul><li>Understand and explain general principles… </li></ul><ul><ul><li>Layered protocols </li></ul></ul><ul><ul><li>Indirection in naming </li></ul></ul><ul><ul><li>Packet routing </li></ul></ul><ul><ul><li>Local and hierarchical namespaces </li></ul></ul><ul><ul><li>End-to-end principle </li></ul></ul><ul><li>… As applied to Internet </li></ul><ul><ul><li>IP/TCP/HTTP </li></ul></ul><ul><ul><li>DNS and IP addresses </li></ul></ul><ul><ul><li>Pressures for Internet evolution </li></ul></ul><ul><li>Understand structure of ISP industry </li></ul><ul><li>Diagnose connection troubles </li></ul>
    6. 6. Learning Objectives <ul><li>Understand the Internet protocol stack </li></ul><ul><li>Understand what IP provides and how it provides it </li></ul><ul><ul><li>Understand IP addresses & packet routing </li></ul></ul><ul><li>TCP </li></ul><ul><li>More advanced topics </li></ul><ul><ul><li>The end-to-end principle </li></ul></ul><ul><ul><li>Quality of service </li></ul></ul><ul><ul><li>Pricing </li></ul></ul><ul><li>HTTP </li></ul><ul><li>Web server administration </li></ul>Future sessions
    7. 7. Simplified Internet Topology Hosts Routers/Switches Access links Backbone links
    8. 8. Terminology <ul><li>A network is the collection of routers, communication lines and hosts controlled by a network operator (or an organization or a homeowner) </li></ul><ul><ul><li>In the diagram, these are the matching yellow ovals and white lines that connect them </li></ul></ul><ul><li>An internet is a network of networks </li></ul><ul><li>The Internet is the public network of networks we use all the time </li></ul>
    9. 9. Conceptual Layering of Internet Protocols/Services Internet Protocol (IP) Subnets User Datagram Protocol (UDP) Transmission Control Protocol (TCP) HyperText Transport Protocol (HTTP) Application Real-time Transport Protocol (RTP) Application Layer Transport Layer Network Layer Data Link and Physical Layer Internet Protocol (IP) Last week’s topic Today’s topic Each layer provides services to the layer above, and utilizes service provided by the layer below
    10. 10. Comparing the OSI and TCP/IP Reference Models Data Link Physical Network Transport Presentation Session Application Host-to- Network Transport Application Internet
    11. 11. Questions
    12. 12. Network/Internet Layer <ul><li>Responsible for routing packets from source to destination </li></ul><ul><ul><li>Not responsible for the packet’s payload </li></ul></ul><ul><li>IP is common </li></ul><ul><ul><li>IPX (Novell Netware) is another </li></ul></ul><ul><li>Next we’ll discuss IP in terms of its </li></ul><ul><ul><li>Service </li></ul></ul><ul><ul><li>Protocol </li></ul></ul>
    13. 13. IP Service <ul><li>Provides best effort packet delivery </li></ul><ul><ul><li>Between two hosts </li></ul></ul><ul><ul><li>Not necessarily sharing a common LAN or subnet </li></ul></ul><ul><li>How </li></ul><ul><ul><li>Global addressing </li></ul></ul><ul><ul><li>Packet forwarding </li></ul></ul>
    14. 14. IP Protocol <ul><li>The IP protocol specifies three things </li></ul><ul><ul><li>IP packet format </li></ul></ul><ul><ul><li>IP addresses </li></ul></ul><ul><ul><li>IP packet routing </li></ul></ul>
    15. 15. IP Protocol: Packet Format <ul><li>Header </li></ul><ul><ul><li>Source IP address </li></ul></ul><ul><ul><li>Destination IP address </li></ul></ul><ul><ul><li>HopLimit </li></ul></ul><ul><ul><li>Payload length </li></ul></ul><ul><li>Payload </li></ul><ul><ul><li>Actual data </li></ul></ul>Header Payload
    16. 16. IP Protocol: Addresses <ul><li>Every host gets a distinct address </li></ul><ul><ul><li>Can be dynamically assigned </li></ul></ul><ul><li>IPv4 (currently ubiquitous) </li></ul><ul><ul><li>Each address 32 bits </li></ul></ul><ul><ul><li>Divide into 8 bit segments </li></ul></ul><ul><ul><li>Example: 141.211.203.32 </li></ul></ul><ul><ul><li>4 billion addresses </li></ul></ul><ul><li>IPv6 (future widespread adoption?) </li></ul><ul><ul><li>Each address 128 bits </li></ul></ul><ul><ul><li>“ 1500 addresses per square foot” </li></ul></ul>
    17. 17. IP Address Assignment <ul><li>Fixed (static) IP address </li></ul><ul><ul><li>Computer always has same IP address </li></ul></ul><ul><li>Dynamic IP address </li></ul><ul><ul><li>Address changes each time computer connects to network </li></ul></ul><ul><ul><li>Internet Access Provider (U-M, AOL, MSN, etc.) assigns an address from its pool </li></ul></ul><ul><ul><ul><li>Uses DHCP to allocate addresses </li></ul></ul></ul><ul><ul><ul><li>All addresses in that pool are routed to the provider </li></ul></ul></ul><ul><ul><ul><li>Provider forwards on to correct final destination </li></ul></ul></ul>
    18. 18. Questions
    19. 19. IP Protocol: Routing <ul><li>Final destination IP address written in packet </li></ul><ul><ul><li>Not the full route </li></ul></ul><ul><li>Each router has connections to several hosts </li></ul><ul><li>Each router keeps a table that indicates where to go based on final destination </li></ul><ul><li>Reducing table size </li></ul><ul><ul><li>use wildcards: 141.211.* next hop is X </li></ul></ul>Final Destination Next hop 141.211.203.032 X 207.075.186.001 Y
    20. 20. IP Routing Demonstration #1 <ul><li>Envelope is an IP packet </li></ul><ul><ul><li>Inside is the payload (a bit string) </li></ul></ul><ul><ul><li>Outside specifies a destination in the format ( subnet, ID ) </li></ul></ul><ul><li>If you have two packets, drop the second one </li></ul><ul><li>Consult your routing table </li></ul><ul><ul><li>Routers with ID of 0 can pass packets to different subnets </li></ul></ul><ul><ul><li>All other routers must pass to router at ID 0 if packet needs to reach another subnet </li></ul></ul><ul><ul><li>Routers send packets on destination subnet to correct ID </li></ul></ul><ul><ul><li>If destination subnet and ID match your address, open the envelope </li></ul></ul>
    21. 21. Routing Changes <ul><li>Routers talk to each other (e.g., BGP protocol) </li></ul><ul><ul><li>Advertise routes </li></ul></ul><ul><ul><ul><li>“I’m now accepting traffic for 141.211.*” </li></ul></ul></ul><ul><ul><li>Query for route availability </li></ul></ul><ul><ul><ul><li>“Is anyone accepting traffic for 141.211.*?” </li></ul></ul></ul><ul><li>Update entries in own routing table </li></ul>
    22. 22. Routing Dangers <ul><li>Long routes </li></ul><ul><li>Circular routes </li></ul><ul><ul><li>Use “HopLimit” to limit damage </li></ul></ul><ul><ul><li>Decrement HopLimit at each router </li></ul></ul><ul><ul><li>Discard packet if HopLimit=0 </li></ul></ul><ul><li>Hijacking routes </li></ul><ul><ul><li>Advertise a route, but don’t deliver </li></ul></ul><ul><li>Route flapping </li></ul><ul><ul><li>Frequent updates to routing table </li></ul></ul>
    23. 23. IP Routing Demonstration #2: HopLimit <ul><li>Revised routing rules </li></ul><ul><ul><li>Decrement HopLimit (cross out and write next smaller number) </li></ul></ul><ul><ul><ul><li>If HopLimit=0 then drop packet </li></ul></ul></ul><ul><ul><li>If you have two packets, drop the second one </li></ul></ul><ul><ul><li>Consult your routing table </li></ul></ul><ul><ul><ul><li>Routers with ID of 0 can pass packets to different subnets </li></ul></ul></ul><ul><ul><ul><li>All other routers must pass to router at ID 0 if packet needs to reach another subnet </li></ul></ul></ul><ul><ul><ul><li>Routers send packets on destination subnet to correct ID </li></ul></ul></ul><ul><ul><ul><li>If destination subnet and ID match your address, open the envelop </li></ul></ul></ul>
    24. 24. Summary: Why Delivery Not Guaranteed <ul><li>Intermediate host not responding </li></ul><ul><ul><li>Temporary malfunction </li></ul></ul><ul><ul><li>Queues full (congestion) </li></ul></ul><ul><li>Bad routing </li></ul><ul><ul><li>Reach hop limit because route was too long or circular </li></ul></ul>
    25. 25. Sharing an IP Address? <ul><li>DSL provider gives me one IP address </li></ul><ul><li>I have several devices on my home network? </li></ul><ul><ul><li>How many do you have? </li></ul></ul><ul><li>How does it work? </li></ul>
    26. 26. Fetching A Web Page www.si.umich.edu Home computer MichNet Modem 207.75.186.1 198.108.3.5 141.211.0.9 141.211.203.32 c-ccb2 router c-ugli router
    27. 27. TRACERT SI.UMICH.EDU 1 * Request timed out. 2 140 ms 207.75.186.1 3 140 ms f-umbin.c-ccb2.umnet.umich.edu [198.108.3.5] 4 240 ms f-backbone.c-ugli.umnet.umich.edu [141.211.0.9] 5 141 ms bart.si.umich.edu [141.211.203.32] www.si.umich.edu Home computer MichNet Modem 207.75.186.1 198.108.3.5 141.211.0.9 141.211.203.32 c-ccb2 router c-ugli router
    28. 28. IP As Spanning Layer IP IP IP Network 1 Network 2 TCP or UDP TCP or UDP Host A Host B Application Application Switch or Router Diversity <ul><li>A spanning layer is a common protocol offering consistent services and interfaces to the layers above it that has been implemented on a wide range of underlying networking technologies, such as Ethernet and token ring </li></ul>N 2 N 1
    29. 29. What IP Doesn’t Do <ul><li>Guarantee speed of delivery </li></ul><ul><li>Guarantee delivery </li></ul><ul><li>Guarantee order of delivery </li></ul><ul><li>Maintain conversational context (each packet is independent) </li></ul><ul><li>Specify a process that should handle the packet at destination </li></ul>
    30. 30. IP over Voice Gateway Public telephone network Internet Computer w/modem    Computer w/modem
    31. 31. Voice over IP Gateway Public telephone network Internet IP telephone or computer running VoIP software Plain old telephone   
    32. 32. Summary <ul><li>The Internet protocol stack defines several protocol layers that work together to deliver Internet traffic </li></ul><ul><li>IP provides best effort packet delivery using </li></ul><ul><ul><li>Global addresses </li></ul></ul><ul><ul><li>Store-and-forward routers </li></ul></ul><ul><li>IP is a spanning layer </li></ul><ul><ul><li>Available on a wide range of network architectures, with a variety of applications built on top of it </li></ul></ul><ul><li>But there are lots of things that IP doesn’t do </li></ul><ul><li>Next time, TCP… </li></ul>
    33. 33. IP over Voice Gateway Public telephone network Internet Computer w/modem    Computer w/modem
    34. 34. Voice over IP Gateway Public telephone network Internet IP telephone or computer running VoIP software Plain old telephone   

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