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Jennifer Rexford Fall 2014 (TTh 3:00-4:20 in CS 105) COS 561: Advanced Computer Networks

Measurement. Jennifer Rexford Fall 2014 (TTh 3:00-4:20 in CS 105) COS 561: Advanced Computer Networks http://www.cs.princeton.edu/courses/archive/fall14/cos561/. Why Measure?. Managing protocols Generating reports Diagnosing problems Tuning network configuration Planning future capacity

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Jennifer Rexford Fall 2014 (TTh 3:00-4:20 in CS 105) COS 561: Advanced Computer Networks

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  1. Measurement Jennifer Rexford Fall 2014 (TTh 3:00-4:20 in CS 105) COS 561: Advanced Computer Networks http://www.cs.princeton.edu/courses/archive/fall14/cos561/

  2. Why Measure? • Managing protocols • Generating reports • Diagnosing problems • Tuning network configuration • Planning future capacity • Evaluating protocols • Characterizing protocol behavior in the wild • Creating realistic models to drive protocol evaluation

  3. What to Measure • Traffic • Routing • Topology • Performance

  4. Traffic Measurement

  5. Shared media (Ethernet, wireless) Multicast switch Host A Host C Monitor Host A Host B S w i t c h Host B Monitor Monitor Splitting a point-to-point link Router B Router A How to Monitor a Link Line card that does monitoring Router A

  6. Subselecting the Traffic • Look at a subset of the packets • Filter on packet-header fields • Sample packets (e.g., 1 out of 1000) • Collect the first n bytes of packet • Medium access control header (if present) • IP header (typically 20 bytes) • IP+UDP header (typically 28 bytes) • IP+TCP header (typically 40 bytes) • Application-layer message (entire packet) • What can you learn?

  7. Data Analysis Challenges • Mapping IP addresses to names, users, institutions • Mapping transport port numbers to applications • Reconstructing application messages from packets • Missing data (sampling, monitor overload) • Routing changes • Asymmetric routing

  8. Data Aggregation: Flow Monitoring • Grouping packets into flows • Packets with the same header fields • Close together in time • Approximating a “conversation” • Without access to the end-hosts • E.g., NetFlow, sFlow flow 4 flow 1 flow 2 flow 3

  9. Recording Flow Statistics • Packet header fields • Source and destination IP addresses • Source and destination TCP/UDP port numbers • Other IP & TCP/UDP header fields • Location • Input and output ports • Aggregate statistics • Start and finish time • Number of bytes or packets • Summary of TCP flags SYN ACK ACK FIN finish start 4 packets 1436 bytes SYN, ACK, & FIN

  10. Network-Wide Traffic Measurement • Observe directly as packets flow • Observe at ingress and project to paths • Infer from link loads and routing fine grained: path matrix = bytes per path current state &traffic flow predicted control action: impact of routing traffic matrix = bytes per ingress-egress

  11. Routing

  12. Monitoring the Routes • Control plane • Routing-protocol messages • Techniques • Dump state from one or more routers • Participate in the routing protocol • Collect packets from routing-protocol messages • Challenges • Cooperation of the network administrator • Collection from enough vantage points • Delays in propagating routing messages

  13. Monitoring Link-State Routing • Flooding of link-state advertisements • All routers knows the entire topology • Can dump the state of any router • Monitor can participate in the routing protocol • Can collect the routing-protocol messages 2 1 3 1 4 2 1 5 4 3

  14. Monitoring Path-Vector Routing • Propagating a path to each neighbor • A router knows the path used by each neighbor • Monitor can become a neighbor of a router • Multiple vantage points to achieve coverage BGP session Monitor BGP session

  15. BGP Table (“show ip bgp” at RouteViews) NetworkNext HopPath * 3.0.0.0/8 205.215.45.50 4006 701 80 * 167.142.3.6 5056 701 80 * 157.22.9.7 715 1 701 80 * 195.219.96.239 8297 6453 701 80 * 195.211.29.254 5409 6667 6427 3356 701 80 *>12.127.0.2497018 701 80 * 213.200.87.254 3257 701 80 * 9.184.112.0/20 205.215.45.50 4006 6461 3786 * 195.66.225.254 5459 6461 3786 *>203.62.248.41221 3786 * 167.142.3.6 5056 6461 6461 3786 * 195.219.96.239 8297 6461 3786 * 195.211.29.254 5409 6461 3786 AS 80 is General Electric, AS 701 is UUNET, AS 7018 is AT&T AS 3786 is DACOM (Korea), AS 1221 is Telstra

  16. Measuring the Forwarding Path • Data plane • What path is the traffic taking • Techniques • Extract the forwarding-table state • Record the path as the packet travels • Infer the path from end-to-end measurements • Challenges • Cooperation of the network administrator • Routing changes during the measurement • Overhead of collecting the data

  17. TTL=2 Traceroute • Time-To-Live field in IP packet header • Source sends a packet with a TTL of n • Each router along the path decrements the TTL • “TTL exceeded” sent when TTL reaches 0 • Traceroute tool exploits this TTL behavior Time exceeded TTL=1 destination source Send packets with TTL=1, 2, 3, … and record source of “time exceeded” message

  18. From My House to Princeton CS • 1 192.168.0.1 (192.168.0.1) • 2 c-68-37-226-1.hsd1.nj.comcast.net (68.37.226.1) • 3 xe-2-1-0-sur01.hillsboro.nj.panjde.comcast.net (68.85.119.149) • 4 ae-18-0-ar03.plainfield.nj.panjde.comcast.net (68.85.62.65) • 5 he-3-10-0-0-cr01.newyork.ny.ibone.comcast.net (68.86.93.225) • 6 he-0-12-0-0-pe03.111eighthave.ny.ibone.comcast.net (68.86.83.106) • 7 be7922.ccr21.jfk10.atlas.cogentco.com (154.54.13.161) • 8 be2057.ccr22.jfk02.atlas.cogentco.com (154.54.80.177) • 9 te0-0-2-1.rcr12.phl03.atlas.cogentco.com (154.54.27.118) • 10 te0-0-2-1.rcr12.phl03.atlas.cogentco.com (154.54.27.118) • 11 38.122.150.2 (38.122.150.2) • 12 core-87-router.princeton.edu (128.112.12.130) • csgate.princeton.edu (128.112.12.58) • ...

  19. RocketFuel Paper Discussion

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