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

2. Project 1 in, Project 2 out (Friday) 2  Project 1 will be graded next week  Project 2 out Friday

3. Firewall vs closed port 3  Inside rack  Port 27993 OK  Port 27992 ICMP type 3 (destination unreachable)

4. Firewall vs closed port 4  Outside rack  Port 27993 OK  Port 27992 Blocked (no response) Timeout

5. Summary from last class 5  C Sockets  Physical layer  Move bits around  Synchronize to determine when bits start/end  Link Layer  Framing  Error detection

6. Today’s class 6  Paper reviews  Spanning Tree  OSPF in operational networks  Network layer  Addressing  Routing  Packet delivery  Intradomain routing  Next week: Interdomain routing

7. Perlman paper 7  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

8. Perlman paper (2) 8  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

9. Shaikh paper 9  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

10. Shaikh paper (2) 10  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.