Multipath tracing with Paris Traceroute Brice Augustin Timur

Multipath tracing with Paris Traceroute Brice Augustin Timur Friedman and Renata teixeira Laboratoire LIP 6 – CNRS Université Pierre et Marie Curie – Paris 6

Introduction § Traceroute measures a path between two hosts in an IP network § It is widely used 1 – Diagnosis of connectivity problems [Paxson 1999] – Inferrence of network properties [Faloutsos 1999] – Internet maps [Rocketfuel 2002]

Contributions § Previously [IMC 2006]: identified traceroute deficiencies on load balanced paths § Measured paths are: § – Inaccurate (fixed) – Incomplete (this remained to be done) Built a new traceroute: Paris traceroute – 2 Added a probing algorithm to trace all paths

Traceroute under load balancing Actual topology: Src A C TTL = 2 L B E Dst D TTL = 3 Inferred topology: Src A E L B Missing nodes and links 3 C False link D Dst

Tracing a single path [IMC 2006] § Solves the problem with per-flow load balancing – Probes have the same flow identifier Port 1 A Port 1 C Port 1 Src TTL = 2 L B TTL = 1 4 TTL = 3 D E Dst

Tracing all the paths 5 § Multipath Detection Algorithm (MDA) § Change the probing strategy § At each hop: – Send probes with a different flow identifier – Send enough probes to enumerate all interfaces with a high degree of confidence – Classify load balancers: per-flow or per-packet

MDA - interfaces enumeration Steps: Port 811 Port 124 Port A ? § § § Src L Port 910 Port 3567 Port ? B TTL = 1 Parameters: • 95% confidence degree 6 § § ? § Nexthops of L? Suppose 2 interfaces Send 6 probes through L Responses from 2 interfaces Suppose actually 3 interfaces Send 5 more probes through L No third interface Stop probing

MDA – hop by hop progression Port 12 Port 811 Port Port 124 Port C ? ? A Src L ? TTL = 2 ? B 7 C E Dst Next steps: § D Nexthops of A? § Find enough probes traversing A § Enumerate interfaces

MDA - load balancer classification Port 11 Port 111 Port 1 Steps: Per-packet or per-flow A Src L TTL = 1 8 Port 1 B ? § Suppose per-packet § Send 6 identical probes § Responses from 2 1 interfaces interface

Measurement infrastructure 5000 reachable destinations Measurements • 1 round takes 100 minutes Paris traceroute Classic traceroute Paris INTERNET Source 9 Paris traceroute

Number of interfaces Paris traceroute performance 20 Discovered (+) + Missed (-) * 15 10 Paris traceroute 201 cases where Paris traceroute finds up to 1 16 more interfaces missed or more 5 Paths with load balancing: - per-flow: 30% Paris traceroute finds one more - per-packet: 2% interface than classic traceroute 0 -5 -10 0 400 800 1200 Destination 10 1600

The effects of load balancing # distinct hops 1000 100 Most hops have a small number ICMP probing usually discovers of responding interfaces fewer interfaces Some hops have up to 16 interfaces 10 1 11 UDP probing ICMP probing 2 4 6 8 10 12 14 # interfaces per hop 16

Conclusion 12 § It no longer makes sense to trace a single route from source to destination in the internet § Classic traceroute discovers incomplete paths § Paris traceroute and the MDA trace all paths to a destination with a high level of confidence

Perspectives § Measure “native path diversity” in the internet (submitted to IMC 2007) § Handle some probing subtleties § Simple extensions to detect: § 13 – Per-destination load balancing – Uneven load balancing Return path diversity

More information www. paris-traceroute. net 14

Contributions § § Identified traceroute deficiencies on load balanced paths √ Measured paths are inaccurate [IMC 2006] – Measured paths are incomplete Built a new traceroute: Paris traceroute § 15 Added a probing algorithm to trace all paths

Traceroute under normal case Actual topology: Src Dst B A TTL = 3 TTL = 2 TTL = 1 Inferred topology: Src 16 A B Dst

Tracing all the paths § Multipath Detection Algorithm (MDA) § Change the probing strategy: – – – 17 Adapt the number of probes at each hop Enumerate the nexthops of load balancers with a high degree of confidence Classify load balancers

Tracing a single path [IMC 2006] § another dest to Solves the problem with per-flow. Add load balancing – show that we Probes have the same flow identifier discover the other path ? Port 1 A Port 1 C Port 1 Src TTL = 2 L B TTL = 3 D TTL = 1 18 Show a problem on link B – D. can’t see it if trace only upper path E Dst

The effects of load balancing # distinct hops 1000 100 probing usually discovers Most ICMP hops have a small number fewerinterfaces of reachable Some hops have up to 16 interfaces 10 1 19 UDP probing ICMP probing 0 2 4 6 8 10 12 14 16 # interfaces per hop

Number of interfaces Paris traceroute performance 20 Discovered (+) + Missed (-) * 15 10 Paris traceroute 201 cases where Paris traceroute finds up to 16 more interfaces missed 1 or more interfaces 5 0 Paris traceroute finds one more interface than classic traceroute -5 -10 0 400 800 1200 Destination 20 1600