Paris traceroute: Measuring more accurate and complete paths

Transcription

1 Paris traceroute: Measuring more accurate and complete paths rice ugustin Fabien Viger, Xavier uvellier, Matthieu atapy, lémence Magnien, Timur Friedman and Renata Teixeira aboratoire IP6 NRS Université Pierre et Marie urie Paris 6

2 What s wrong with traceroute? -bash-3.00$ traceroute -n ms ms ms ms ms * ms ms ms ms ms * ms ms ms ms ms * ms ms ms ms ms ms ms ms ms ms ms ms ms ms ms ms ms ms 1

3 What s wrong with traceroute? -bash-3.00$ traceroute -n ms ms ms ms ms * ms ms ms ms ms * ms ms ms ms ms * ms ms ms ms ms ms F ms ms ms E ms ms ms ms ms ms ms ms ms G H J N K 2

4 Findings Identified traceroute deficiencies on load balanced paths Measured paths are inaccurate and incomplete May diagnose an incorrect path Many routers have load balancing capabilities Per-packet, per-flow, per-destination uilt a new traceroute: Paris traceroute 3

5 lassic vs Paris traceroute lassic traceroute: E G H J N K F Paris traceroute: K F E G H I J M N 4

6 Traceroute under load balancing ctual network: TT = 2 E Inferred path: TT = 3 False link E Missing nodes and links 5

7 Hard to diagnose aberrant paths ctual network: TT = 3 TT = 4 Inferred path: TT = 2 6

8 Hard to diagnose unstable paths ctual network: E Inferred path: E 7

9 Problems happen even under per-flow load balancing Port 2 Flow 1 Port 1 TT = 2 Port 3 E TT = 1 TT = 3 Traceroute uses the destination port as identifier Per-flow load balancers use the destination port as part of the flow identifier 8

10 Paris traceroute: Tracing a single path Solves the problem with per-flow load balancing Packets have the same flow identifier Works with UP, TP and IMP Port 1 Port 1 Port 1 TT = 2 TT = 3 E TT = 1 9

11 Identifying the probes IPv4 header V/ihl TOS ength Identifier Fragment TT Proto hecksum Source address estination address Payload Source port est. port Type ode hecksum ength hecksum Identifier Sequence Payload Payload UP header IMP header 10

12 Paris traceroute: Tracing all the paths hange the probing strategy t each hop: Send packets with a different flow identifier Send enough probes to enumerate all interfaces with a high degree of confidence lassify load balancers: per-flow or per-packet 11

13 Interfaces enumeration TT = 1 Port Port Port Port ? Port Port Port ?? Steps: Interfaces after? Suppose 2 interfaces Send 6 packets through Responses from 2 interfaces Suppose actually 3 interfaces Send 5 more packets through No third interface Stop probing 12

14 Probing overhead per hop lassic traceroute: 3 packets by default Paris traceroute: at least 6 packets to rule out load balancing # interfaces # packets Up to 96 probes (up to 16 responding interfaces in our traces) 13

15 Paris traceroute output -bash-3.00$ paris-traceroute n a exh [...] :0,1,3,6,9, :2,4,5,7, :0,1,3,6,9, :2,4,5,7, :0,1,3,6,9, :2,4,5,7, :0,1,3,6,9, :2,4,5,7, [...] Single path, no load balancing Per-flow load balancer 2 load-balanced paths ist of flow identifiers 14

16 oad balancing is common Measurements from 15 sources to 70,000 destinations Paths affected by load balancing: 39% by per-flow 2% by per-packet 70% by per-destination Many Tier-1s use load balancing 15

17 oad balancing causes anomalies From our IP6 vantage point: iamonds appear in 30% of the destinations Paris traceroute removes 10,662 from 19,159 (56%) oops appear in 4.5% of the measured routes Paris traceroute removes 5,047 from 5,795 (87%) ycles appear in 0.25% of the measured routes Paris traceroute removes 3,886 from 5,674 (68%) Other causes Routing changes NT boxes uggy routers Per-packet load balancing 16

18 oad-balanced paths Generally short, narrow and symmetric Some are extremely long More than 10 hops Some others are very wide Up to 16 responding interfaces Parallel paths with different hop counts 17

19 onclusion Vast deployment of load balancing lassic traceroute discovers inaccurate and incomplete paths Paris traceroute reports more accurate and complete paths 18

20 More information 19

21 Perspectives Measure native path diversity in the internet (submitted to IM2007) Handle some probing subtleties Simple extensions to detect: Per-destination load balancing Uneven load balancing Return path diversity 20

22 ackup slides/making of 21

23 Hop by hop progression Port Port Port Port 12 Port Port Port ?? TT = 2?? E Next steps: Nexthops of? Find enough packets traversing Enumerate interfaces 22

24 oad balancer classification Port Port Port Port Port Port 1 Steps: Port 1 Port 1 Per-packet or per-flow Suppose per-packet? TT = 1 Send 6 identical packets Responses from 12 interfaces 23

25 What s wrong with traceroute? -bash-3.00$ traceroute -n ms ms ms ms ms * ms ms ms ms ms * ms ms ms ms ms * ms ms ms ms ms ms ms ms ms ms ms ms ms ms ms ms ms ms H E G J F N K 24

26 Introduction Traceroute measures a path between two hosts in an IP network It is widely used by: Network operators Networking researchers Geeks/omputer enthusiasts 25

27 Hard to diagnose aberrant paths Inferred path: ctual network: TT = 3 TT = 4 TT = 2 26

28 Hard to diagnose unstable paths Inferred path: E ctual network: E 27

29 Introduction K E G H F J N 28