Presentation given regarding ISP Mapping, based on a paper which presents Rocketfuel by Spring et al.

1. ISP Mapping
(Rocketfuel)
Simon Wadsworth
Based on ”Measuring ISP Topologies with Rocketfuel” by Spring et al.

2. Why map ISPs?
● Real topologies not public
● Want to see router level conectivity and POP
structure

3. An ISP
● ISP consists of a bunch of POPs connected by a
”backbone”
● Routers connected to backbone links are
”backbone” or ”core” routers
● Every POP has access
routers providing layer
between ISP backbone
and neighboring networks

4. Selecting Measurements
● Only need to take traceroutes expected to transit
ISP
● Only need to take one traceroute when two or more
enter and leave the ISP at the same point
● So make use of Directed Probing and Path
Reductions

5. Directed Probing
● Identify traceroutes that transit ISP
● Dependent prefixes
● Prefixes originated by the ISP or single­homed
customers
● All traceroutes to prefix should transit ISP
● Identified from BGP table
● Insiders
● From traceroute server in a dependent prefix

6. Directed Probing
● Up/down traces
● Likely to transit ISP based on AS­path

7. Path Reductions
● Ingress Reduction
● Two traceroutes from different vantage points to
same destination enter at same point
● Egress Reduction
● Traceroutes from same ingress to any prefix behind
same egress witll be same path
● Next­hop AS Reduction
● Path depends on next­hop AS
● Only one race from ingress router to next­hop AS
is valuable

8. Alias Resolution
● Found Mercator was efficient, but missed many
aliases
● Created Ally, the IP­ID based method of Alias
Resolution
● It finds 3x as many Aliases as previous methods

9. Router Identification
● DNS
● Geographical Location
● Role in topology
● s1­bb11­nyc­3­0.sprintlink.net
● Sprint Backbone Router
● P4­0­0­0.r01.miamifl01.us.bb.verio.net
● Verio Backbone router

10. Rocketfuel

11. Rocketfuel
● Egress Discovery
● Find the egress routers, traceroute to each dependent
prefix from a local machine
● Dependent prefixes may be aggregated
● Break them into /24's
● Tasklist Generation
● Use BGP tables to generate list of directed probes
● Dependent prefixes in directed probes replaced with
egresses, and duplicates removed

12. Rocketfuel
● Path Reductions
● Take tasklist, apply ingress and next­hop AS
reductions and generate jobs
● Checks if predicted ingress or egress was used, then
job is complete, otherwise other vantage point is
chosen
● Execution Engine
● Handles load­limiting, load balancing and different
formats of traceroute output

13. Evaluation
● Asked ISPs to validate results – Three ISPs assisted
● ISPs said they didn't miss any POPs
● ISPs said they didn't miss any links between POPs
● Missed some access routers
● Received a Good, Very good and Vgood to Excellent
rating from the ISPs
● IP address space
● Scans 60 /24s looking for new routers
● They found that they found approximately 48.6 to
78.9% of the routers

14. Evaluation
● Comparison with RouteViews
● Check number of adjacencies seen in maps compared
to RouteViews
● Router­level map should include one link from a
router to one in neighboring AS
● Worst case was 70%
● Comparison with Skitter
● Found 7x as many routers, links and IPs by Skitter

15. Impact of Reductions
● Reduced number of traces down to 0.1% of those
required by a brute­force technique
● Scales well with number of vantage points

16. Questions