2. Efficient Algorithms for Large-Scale Topology Discovery Benoit Donnet joint work with Philippe Raoult, Timur Friedman and Mark Crovella Sigmetrics 2005 – Banff (Canada)

3. Context ● Network measurement ● Internet topology discovery using distributed traceroute monitors – IP interface level ● Existing tools: – Skitter (CAIDA) – TTM (RIPE NCC) – AMP (NLANR) – DIMES (Tel Aviv U.)

4. Scaling Problem ● More monitors means more load on – network resources – destinations ● Classical approaches either – stay small (skitter, TTM, AMP) – trace slowly (DIMES) ● Can we trace more efficiently?

5. Contributions ● Quantification of scaling problems – Intra-monitor redundancy – Inter-monitor redundancy ● Efficient cooperative topology discovery algorithm – Doubletree

6. Intra-monitor Redundancy (1)

7. Intra-monitor Redundancy (2)

8. Inter-monitor Redundancy (1)

9. Inter-monitor Redundancy (2)

10. Doubletree: Tree-like Structure of Routes ● Both redundancy (i.e. inter and intra) suggest two different probing schemes – They are based on the tree-like structure of routes ● Intra-monitor – monitor-rooted tree (first suggested by Govindan et al.) ● Inter-monitor – destination-rooted tree

11. Doubletree: Monitor-rooted Tree

12. Doubletree: Destination-rooted Tree

13. Doubletree: Reconciliation ● Backward and forward probing are opposite schemes ● How can we reconciliate them? – Starts probing at some hop h ● First, performing forward probing from h ● Second, performing backward probing from h-1

14. Doubletree: Stop Sets ● Not necessary to maintain the whole tree structure. ● Each monitor uses stop sets: {(interface, root)} – Local Stop Set B: {interface} ● Backward probing – Global Stop Set F: {(interface, destination)} ● Forward probing ● Shared between monitors

15. Doubletree: Results (1) Intra-Monitor skitter Doubletree

16. Doubletree: Results (2) Inter-Monitor skitter Doubletree

17. Conclusion ● We point out redundancy in classical topology discovery approaches using two metrics: – Intra-monitor redundancy – Inter-monitor redundancy ● Based on these metrics, we define the Doubletree algorithm: – Measurement load reduction up to 76% – Interface and link coverage above 90%