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Re: [RRG] Routers in DFZ - reliable figures from iPlane

Robin,
iPlane is doing a great job going further in revealing the structure of the network. Said that, I think you probably need to rephrase some of the statements bellow. 


     Singlehomed routers:            87k
     Routers in Default Free Zone:  123k

     Total BGP routers:             210k
1. What do you call DFZ routers are not DFZ, i.e. DFZ is not the same as multihomed, a stub can be multihomed and only use half of the routing table, the other half use default routing. What you call singlehome may not be singlehome because of the limited visibility of iPlane.
2. These numbers are at most a lower bound on the numbers you are looking for, and we have no way to tell how tight this bound is. iPlane data is incomplete because of several reasons, such as limited number of vantage points, blocking of ICMP/UDP by routers, MPLS tunnels,.... Furthermore, there's the problem of converting router interfaces to AS numbers which is not entirely resolved, see these papers: 
http://irl.cs.ucla.edu/topology/chang01inferring.ps
http://irl.cs.ucla.edu/topology/fwdPath.pdf
http://irl.cs.ucla.edu/topology/3rdparty.pdf



We are currently considering a major, kludgey, mapping and tunneling
overlay architecture to add to the Internet, in addition to moderate
and generally improvements to the BGP protocol itself.  Before
anyone could do a cost-benefit analysis of this, they would need an
estimate of how many DFZ routers are afflicted by the problems which
prompted us to propose such a drastic solution.  They would need to
roughly characterise those routers in terms of their model number,
number and capacity of interfaces etc. - and also their cost.
And getting realistic numbers for those is an unfeasible task as of now, at least for the entire Internet. My advice is to get accurate data for a tier-1 ISP directly and start from there. 



According to my understanding of this file, each line represents a
BGP router in the reasonably complete set of traceroutes the iPlane
project works from.  Each line contains an IP address for each of
its interfaces.  So I thought it would be easy to count these, to
find how many had a single IP address - those would be single-homed
routers and the rest would be "multihomed border routers" and
"transit routers" in the DFZ - all with two or more BGP peers.

Nope. A router can have multiple interfaces connecting to same provider.

--Ricardo



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