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CS 4700 / CS 5700 Network Fundamentals

Lecture 7.5 : Summary from Lecture 2. CS 4700 / CS 5700 Network Fundamentals. Revised 1/25/2014. Project 1 in, Project 2 out. Project 1 will be graded this week Project 2 Any questions?. Summary from last class. Physical layer Move bits around

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CS 4700 / CS 5700 Network Fundamentals

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  1. Lecture 7.5: Summary from Lecture 2 CS 4700 / CS 5700Network Fundamentals Revised 1/25/2014

  2. Project 1 in, Project 2 out • Project 1 will be graded this week • Project 2 • Any questions?

  3. Summary from last class • Physical layer • Move bits around • Synchronize to determine when bits start/end • Link Layer • Framing • Error detection • Media Access Control • Collision Avoidance/Detection • Wired/Wireless (sensing/DCF) • Hubs, switches, bridges and spanning trees

  4. Today’s class • Paper reviews • Spanning Tree • OSPF in operational networks • Network layer • Addressing • Routing • Packet delivery • Intradomain routing • Next week: Interdomain routing

  5. Perlman paper • This paper won her a SIGCOMM award in 2010 • Key take-aways • Not reasonable to assume topologies are loop free, and we need a way to route between LANs automatically • Low memory consumption • Scalable bandwidth consumption • Converges quickly • Tunable

  6. Perlman paper (2) • Implementation details • Timers everywhere • How else do we know when a link is down? • Also can prevent transient loops (hold down) • Loop detection/avoidance • This comes up often in networking • Deterministic behavior • Allows operators to reason about changes • Very hard to do in wide area! • Compare this with BGP when we get to it

  7. Shaikh paper • Key take-aways • Understanding the state of large-scale networks is hard • Especially when they are self-managing • Best way to monitor is to participate in the protocol • Real time is critical, so separation of functionality is critical • Offline vs online analysis • Must not adversely affect the network • Modeling the network allows us to identify anomalies • Flaps • Message storms • Etc

  8. Shaikhpaper (2) • Networking and operators • Operators are extremely cautious people • Tend to lack good tools for understanding the network • Routers are not perfect • Router bugs, flapping due to load, improper timers • Generally hard to detect if you’re not looking for it • Humans are definitely not perfect • Bad configs, e.g.

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