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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

Using Packet Histories to Troubleshoot Networks

Presented by: Yi Gao

Emnets Seminar

2014-4-6


Operating networks is hard
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


Packet history
Packet History

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


Basic idea
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


Netsight architecture
NetSight Architecture


Outline
Outline

  • Life of a postcard

  • History assembly

  • Postcard compression

  • Use packet histories

  • Evaluation



Life of a postcard cnt
Life of a Postcard (Cnt.)

  • Step 1:

    • From switch to server


Life of a postcard cnt1
Life of a Postcard (Cnt.)

  • Step 2:

    • From servers to servers


Life of a postcard cnt2
Life of a Postcard (Cnt.)

  • Step 3:

    • From servers to disks


History assembly
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


Postcard compression
Postcard Compression

  • Step 2&3 in the life of a postcard

  • In step 2: Intra-flow compression

  • In step 3: Inter-flow compression


Use packet histories
Use Packet Histories

  • Packet history filter

  • Applications

    • ndb

    • netwatch

    • netshark

    • nprof


Use packet histories pf
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


Use packet histories phf
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}}


Use packet histories applications
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}}]*$



Evaluation overhead
Evaluation - Overhead

  • Without compression

    • 31%

  • With compression

    • 3% ~ 7%


Summary
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



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