A CIDR Prefix Stopping Rule for Topology Discovery Benoit Donnet joint work with Timur Friedman Algotel 2005 – Presqu'Ile de Giens

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.)

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?

Contributions ● Efficient topology discovery algorithm [Sigmetrics2005] – Doubletree ● Communication overhead reduction – Stopping rule based on CIDR prefixes

Doubletree - Basics ● Cooperative algorithm ● Goal: avoiding paths already explored ● Exploit tree-like structure of routes in the internet – from a monitor to a set of destinations ● Backward probing (first suggested by Govindan et al.) – from a set of monitors to a destination ● Forward probing and monitor coordination

Doubletree: Monitor-rooted tree

Doubletree: Destination-rooted tree

Doubletree: Probing scheme ● Two probing schemes: – Backwards – Forwards ● Stop sets = {(interface, root)} – Local Stop Set: B = {interface} – Global Stop Set: F = {(interface, destination)} ● shared by monitors ● Doubletree starts probing at some hop h from the monitor

Limitation ● Communication cost – Global stop set exchange needs too high network resources – Up to 20.6MB for only 50,000 destinations

Destination based stopping rule

Solution ● Communication cost reduction – Destination addresses aggregation through the use of CIDR prefixes – Global stop set of {(interface, prefix_destination)}

Solution (2)

Results (1)

Results (2)

Results (3)

Conclusion ● Improvements to Doubletree – Communication cost reduced ● Future Work – Implementation – BGP-guided topology discovery