Quantifying Violations of Destination-based Forwarding on the Internet

Transcription

1 Quantifying Violations of Destination-based Forwarding on the Internet Tobias Flach, Ethan Katz-Bassett, and Ramesh Govindan University of Southern California November 14, 2012

2 Destination-based Routing Destination: A 1 2 Routing based on destination only Destination Port A 1 B 2 2

3 Destination-based Routing Destination: A 1 2 Routing based on destination only Destination Port A 1 B 2 3

4 Relying on Destination-based Forwarding iplane Information Plane for Distributed Services [IMC 2006] [OSDI 2006] [NSDI 2009] Doubletree Algorithm for Large-Scale Topology Discovery [PAM 2005] [IEEE Comm Journal 2006] Netdiff [NSDI 2008] Reverse Traceroute [NSDI 2010] 4

5 Reverse Traceroute Reverse path stitched together by combining segments with common hops to the same destination Src R5 R4 R3 R2 R1 Dst 5

6 Reverse Traceroute Reverse path stitched together by combining segments with common hops to the same destination Dst R1 R2 R3 Src R3 R4 R5 Src R5 Src Src R5 R4 R3 R2 R1 Dst 6

7 Reverse Traceroute Reverse path stitched together by combining segments with common hops to the same destination Dst R1 R2 R3 Src R3 R4 R5 Src R5 Src Src R5 R4 R3 R2 R1 Dst 7

8 MPLS Router violates Destination-based Routing UT Arlington LEARN (MPLS Tunnel) Abilene U Auckland (New Zealand) Src Dst Packets without MPLS label routed via red path THEnet Grandecom Default routing entry for non-production traffic (traffic without an MPLS label) 8

9 MPLS Router violates Destination-based Routing UT Arlington Src LEARN U Auckland (New Zealand) Dst THEnet Grandecom Reverse Traceroute can produce a reverse path which differs significantly from the ground truth 9

10 Violation Causes Load balancing Destination and flow identifier MPLS tunneling MPLS label only Preferred routes for some customers (source-based) Other routing policies Source (and destination) address only Any header field combination 10

11 Contributions Methodology for detecting destination-based forwarding violations Analysis of violations observed in active measurements 11

12 Measurement Methodology From: Src To: Dst Src R1 R2 R3 Dst Modify the point of injection to elicit violations of destination-based routing 12

13 Measurement Methodology Src R1 R2 R3 Dst Modify the point of injection to elicit violations of destination-based routing 13

14 Measurement Methodology From: Dst To: R2 Src R1 R2 R3 Dst Modify the point of injection to elicit violations of destination-based routing 14

15 Measurement Methodology Response From: R2 To: Dst Src R1 R2 R3 Dst Modify the point of injection to elicit violations of destination-based routing 15

16 Measurement Methodology RR:R1, R2, R3,... RR:R1, R2, Rx,... Src R1 R2 R3 Dst Rx Modify the point of injection to elicit violations of destination-based routing 16

17 Violation Causes Load balancing Destination and flow identifier MPLS tunneling MPLS label only Preferred routes for some customers (source-based) Other routing policies Source (and destination) address only Any header field combination 17

18 MPLS Tunnels Explicit MPLS tunnels MPLS tunnels with default routing Dst 1 Dst 3 Dst 2 18

19 MPLS Tunnels Explicit MPLS tunnels MPLS tunnels with default routing Dst 1 All injected probes regardless of destination) use the non-regular path (orange) Dst 3 Dst 2 19

20 MPLS Tunnels Explicit MPLS tunnels MPLS tunnels with default routing Dst 1 Dst 3 Dst 2 20

21 Results Summary 262,034 traces recorded 39,699 IP addresses targeted 3,777 ASes visited 28.9% of the IP addresses cause violations 1.3% cause paths forking to different ASes 21

22 Violation Types in Targeted Nodes Type Frequency (all forks) Frequency (forking to different ASes) Load balancing 16.1% 0.0% Explicit MPLS tunnel 0.4% 0.0% Default routing 0.3% 0.3% Unclassified 6.9% 1.7% Non-violating / invalid 76.3% 98.0% 22

23 Conclusion More than 25% of the targeted IPs route via multiple paths to a single destination Packets with the same destination are sometimes routed via different ASes Impact on precision Possible prediction of wrong paths e.g. Reverse Traceroute, iplane Impact on recall Missing links during topology discovery e.g. Doubletree Our techniques can be used to increase precision and recall at the cost of additional probing overhead 23

24 Quantifying Violations of Destination-based Forwarding on the Internet Tobias Flach, Ethan Katz-Bassett, and Ramesh Govindan University of Southern California November 14,