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Session B1: The Art of Packet Analysis

Session B1: The Art of Packet Analysis. Hansang Bae Director – Product Architecture Hansang.bae@riverbed.com. Information. YouTube Channel with older sessions etc. www.youtube.com/hansangb www.box.com/Sharkfest2014 Trace files Presentations

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Session B1: The Art of Packet Analysis

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  1. Session B1: The Art of Packet Analysis Hansang Bae Director – Product Architecture Hansang.bae@riverbed.com

  2. Information YouTube Channel with older sessions etc. www.youtube.com/hansangb www.box.com/Sharkfest2014 • Trace files • Presentations • Camtasia recordings (will be up within one month from end of Sharkfest) NET/NET = I’m older than epoch, the beginning of time

  3. Information Q4…2014 (pester me - *PLEASE*) YouTube Channel with older sessions etc. www.youtube.com/hansangb www.box.com/Sharkfest2014 • Trace files • Presentations • Camtasia recordings

  4. TCP – What does it mean? • Reliable – but why? • Connection oriented – very polite protocol • Flow Control – built-in traffic report • Stream oriented – I don’t need no stinkin’ packets! • Sequence numbers – fundamental building block

  5. Troubleshooting TCP Nagle/Delayed Ack • TCP is great for a lot of things, but real-time transactions that require small packets is not one of them. • Nagle’s motivation was to maximize the ratio of packets to data/content. • Delayed-Ack can help in avoiding some “silly window” scenarios. • Nagle has its place and need. Delayed-Ack has its place and need. • However, Nagle + Delayed-ack = Bad news (sometimes). If you are a financial organization, be on the lookout! Sharkfest 2014

  6. Troubleshooting TCP Nagle/Delayed Ack Nagle rules: • If there are unacknowledged in-flight data,new data is buffered • If the data to be sent is < MSS, it is buffered until MSS • RFC896 (Congestion control in IP/TCP internetworks ) When to send data: • Immediately if a full MSS size packet can be sent (at least MSS data is accumulated) • All previously sent data has been acknowledged AND PSH flag is set • PSH flag is set AND the override timeout (0.1 ... 1s) expired • RFC1122 (Requirements for Internet Hosts – Communication Layers) Sharkfest 2014

  7. Troubleshooting TCP Nagle/Delayed Ack Receiver Data is sent in one packet ACK Data is sent in one packet Sender MSS MSS Application data is accumulated until MSS Sharkfest 2014

  8. Troubleshooting TCP Nagle/Delayed Ack PSH Receiver Buffered data is sent in one packet ACK Data is sent Data is sent Sender Application data is being accumulated MSS Sharkfest 2014

  9. Troubleshooting TCP Nagle/Delayed Ack Receiver New data packet is sent Data is sent New small packet (not full MSS)with PUSH flag Sender PSH Transmit timer expires Nagle override timeout (200 ms) Sharkfest 2014

  10. Troubleshooting TCP Nagle/Delayed Ack • TCP is great for a lot of things, but real-time transactions that require small packets is not one of them. Sharkfest 2014

  11. Troubleshooting TCP Nagle/Delayed Ack No more data coming in? I can’t send the ACK until I have some data of my own to send;another packet arrives; or my timer expires ACK delay 200 ms Receiver Data is sent ACK Buffered data is sent Hmm, I can’t send more data now because I haven’t received any ACK yet. Ibetter start buffering! Now I can send more data! Sender PSH MSS Sharkfest 2014

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