[Csci551-talk] [Q] Internet Path Inflation Due...
ramesh sarangarajan
sarangar@usc.edu
Mon, 03 Feb 2003 11:13:28 -0800
<BODY><P>Their earlier paper - <A href="http://citeseer.nj.nec.com/tangmunarunkit01impact.html">http://citeseer.nj.nec.com/tangmunarunkit01impact.html</A> describes the methodology for generating AS overlay maps. <BR><BR>AS level topology was constructed mainly from the oregon route server bgp dumps. <BR>Anybody can get them from <A href="telnet://route-views.oregon-ix.net/">telnet://route-views.oregon-ix.net/</A> - use "show ip bgp" command. The archives are available at <A href="http://archive.routeviews.org/">http://archive.routeviews.org/</A></P>
<P>But, as BGP reveals only the AS preferences instead of actual physical AS connections, the info from "routeviews" is always incomplete. So, other sources like "Internet Routing Registries" like RADB, RIPE (the European registry) are used to fill in the gaps. ( For example <A href="http://www.radb.net/cgi-bin/radb/whois.cgi?obj=128.125.19.146">http://www.radb.net/cgi-bin/radb/whois.cgi?obj=128.125.19.146</A> gives the IRR record for USC web server; <A href="http://www.radb.net/cgi-bin/radb/whois.cgi?obj=AS226">http://www.radb.net/cgi-bin/radb/whois.cgi?obj=AS226</A> gives the record for the corresponding AS)</P>
<P>As providing routing policies in IRRs is optional, some ISPs don't do that. Internet "looking glass" sites like <A href="http://www.traceroute.org">http://www.traceroute.org</A> can help providing more details.</P>
<P>To answer your question, I think the difference is that "actual" AS map was obtained directly from BGP dumps like the Oregon route server (which can be augmented by IRRs & looking glasses); <A href="http://topology.eecs.umich.edu/archive/asgraph.tar.gz">http://topology.eecs.umich.edu/archive/asgraph.tar.gz</A> is one such dataset; the "overlay" maps are drawn on the top of the router-level map (obtained by their mercator tool) using the same info from Oregon+RADB. They built the overlay map to get the actual inter-AS router links. The reason they compared the macroscopic properties of the actual & overlay maps is that they used approximation techniques (like collapsing the disjoint nodes of same AS to the nearest AS) in the overlay constructions.</P>
<P>Someone please correct me if I'm wrong.</P>
<P>-Ramesh</P>
<P><BR><BR>----- Original Message ----- <BR>From: paavany jayanty <pjayanty@usc.edu> <BR>Date: Sunday, February 2, 2003 4:11 am <BR>Subject: [Csci551-talk] [Q] Internet Path Inflation Due... <BR><BR>> Hi, <BR>> <BR>> In the Internet Path Inflation .... paper there is a mention of <BR>> how overlay AS maps are obtained. <BR>> <BR>> I cannot quite get the difference between the "actual AS map" and <BR>> the AS overlay map. <BR>> <BR>> How are the actual AS maps obtained? <BR>> <BR>> <BR>> <BR>> </P></BODY>