Alias Resolution - PowerPoint PPT Presentation

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  1. Alias Resolution Yao Zhao

  2. Why is Alias Resolution Important • Internet Topology Measurement • Traceroute based approaches [Mercator,Rocketfoul] • Traceroute discovers interfaces other than routers • If alias is not resolved • Virtual nodes • Virtual edges • Virtual topology

  3. Existing Alias Resolution Approaches • DNS names • Some IP addresses are associated with the same DNS name • Using ICMP Port Unreachable • Source address of ICMP Port Unreachable is the outgoing interface that sends back ICMP TTL-exceeded. • Monotonically Increasing IP-ID • The IP-ID of two IP addresses are correlated

  4. What Are Unique in A Router • IP-ID counter • Buffer • IP fragment buffer • Rate Limiting Property • Allowed number of packet in a certain time • Periodically Maintenance • “Coffee-break” and most likely occurs when routers push forwarding tables to the line cards. • Fragments purge period

  5. IP Fragments Buffer • Normal case A1B1C1D1A2B2 … A1 A2 B1 B2 C1 D1

  6. IP Fragments Buffer • Buffer full A1B1C1D1E1 A2B2 … E1 A1 B1 A2 C1 B2 D1 C2

  7. IP Fragments Buffer • Not alias A1E1B1F1C1G1D1H1A2E2 … A1 A2 B1 B2 C1 D1 E1 E2 F1 F2 G1 H1

  8. IP Fragments Buffer • Alias A1E1B1F1C1G1D1H1A2E2 … C1 A1 E1 G1 D1 B1 H1 F1

  9. Fragments purge period • If a router cannot assemble a fragment in a certain time, the router may send back “ICMP Reassemble Time Exceed” • Routers do this action periodically. A1 C1 D1 B1 A1 C1 -> IP1 B1 D1 -> IP2

  10. Overall Alias Resolution Process • Preparation • Run traceroute on Planetlab nodes to find routers • Using TTL to identify suspicious alias pairs • Alias resolution • Ally • UDP rate limiting • Fragmentation based approaches

  11. Improvements ICMP (85%) Frag Ally Rate Limit No response (15%) UDP (60%)

  12. Preliminary Results