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Presentation given regarding ISP Mapping, based on a paper which presents Rocketfuel by Spring et al.
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ISP MappingISP Mapping(Rocketfuel)(Rocketfuel)
Simon WadsworthSimon Wadsworth
Based on ”Measuring ISP Topologies with Rocketfuel” by Spring et al.
Why map ISPs?
● Real topologies not public● Want to see router level conectivity and POP
structure
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 accessrouters providing layer between ISP backbone and neighboring networks
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
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
Directed Probing
● Up/down traces● Likely to transit ISP based on ASpath
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
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
Router Identification
● DNS● Geographical Location● Role in topology
● s1bb11nyc30.sprintlink.net● Sprint Backbone Router
● P4000.r01.miamifl01.us.bb.verio.net● Verio Backbone router
Rocketfuel
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
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
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
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
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
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