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Using Packet Histories to Troubleshoot Networks

Using Packet Histories to Troubleshoot Networks. Presented by: Yi Gao Emnets Seminar 2014-4-6. Operating Networks is Hard. Existing network troubleshooting tools traceroute , ping, SNMP, NetFlow , sFlow , … We are still far from an era of automated troubleshooting

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Using Packet Histories to Troubleshoot Networks

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  1. Using Packet Histories to Troubleshoot Networks Presented by: Yi Gao Emnets Seminar 2014-4-6

  2. Operating Networks is Hard • Existing network troubleshooting tools • traceroute, ping, SNMP, NetFlow, sFlow, … • We are still far from an era of automated troubleshooting • What we want to ask the network

  3. Packet History • The route a packet takes through a network plus the switch state and header modifications it encounters at each hop

  4. Basic Idea • Send a control message (postcard) at each hop • In each postcard • A copy of the packet header • The switch ID • The output ports • A version number for the switch forwarding state • Collect and analyze postcards at a server

  5. NetSight Architecture

  6. Outline • Life of a postcard • History assembly • Postcard compression • Use packet histories • Evaluation

  7. Life of a Postcard

  8. Life of a Postcard (Cnt.) • Step 1: • From switch to server

  9. Life of a Postcard (Cnt.) • Step 2: • From servers to servers

  10. Life of a Postcard (Cnt.) • Step 3: • From servers to disks

  11. History Assembly • Step 3 in the life of a postcard • From multiple postcards to assemble a packet history, in case of reordering • Solution • Packet ID hash • Topological sort

  12. Postcard Compression • Step 2&3 in the life of a postcard • In step 2: Intra-flow compression • In step 3: Inter-flow compression

  13. Use Packet Histories • Packet history filter • Applications • ndb • netwatch • netshark • nprof

  14. Use Packet Histories - PF • Postcard Filters (PF) • A filter to match a packet at a hop (a postcard) • A PF for a packet with source IP A, entering switch S at any input port other than port P

  15. Use Packet Histories - PHF • Packet History Filter (PHF) • To express interest in packet histories • Let X be a PF • start at X: ^{{X}} • end at X: {{X}}$ • go through X: {{X}}

  16. Use Packet Histories - Applications • Network Profiler • Profile a particular link • {{--dpid X --outport p}} • Reachability Error • a PHF to specify packets from A destined for B that never reach the intended final hop • ^{{--bpf "ipsrc A and dst B" --dpid X --inportp1}}[^{{--dpid Y --outport p2}}]*$

  17. Evaluation – PHF matching latency

  18. Evaluation - Overhead • Without compression • 31% • With compression • 3% ~ 7%

  19. Summary • Language • Packet History Filter concisely represents packet histories of interest • Applications • Asuite of network diagnosis apps built atop the NetSightAPI • Platform • The design, implementation, and evaluation of NetSight

  20. Thanks!

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