nanog mailing list archives
Re: Geo location to IP mapping
From: sgorman1 () gmu edu
Date: Tue, 16 May 2006 10:38:35 -0400
Well I must admit that zip code was best case under ideal conditions ;-) There are always plenty of exceptions that put sand in the gears. Putting on my conservative hat the approach is more granular than guessing the right country as was being discussed before. My intention was only to infer there is more than one way to approach the problem and an approach that can avoid some of the DHCP issues seen in the datbase approaches. This was work from 6 years ago so a bit fuzzy on the particulars at this point. best, sean ----- Original Message ----- From: "Steven M. Bellovin" <smb () cs columbia edu> Date: Monday, May 15, 2006 10:25 pm Subject: Re: Geo location to IP mapping
On Mon, 15 May 2006 21:49:31 -0400, Marshall Eubanks <tme () multicasttech com> wrote:I seriously doubt this would work to better than the regional area. My zip code (20124) region is about 5 km across, which would be15microseconds in vacuum, and maybe at most 50 micro seconds in glass. So, you would need accuracies at the 10's of microsecond level to specify zip codes. I can believe that you can measure transmission times down afiberand achieve repeatability at the microsecond level - in fact, I remember a Michelson interferometer that they set up at JPL / Goldstone that tested the Sagnac effect in glass, which required substantially better repeatibility than that. But do you really think that you can estimate the router delayon the(for example) 9 hops between here and GMU to better than 1 millisecond each ? (That would imply a 3millisecondrms error if these errors were random and Gaussian, or about1000 kmin vacuum, and maybe 500 km error in glass.) So, I think that this would fail by at least 2 orders ofmagnitude forzip codes in a real operational network. Which coast of the US,sure,but not much better than that.I suspect you can do that; a bigger factor is the link type of the lasthop. Cable modems, DSL, 802.11 -- they all have characteristic delays. The important insight is that you care about *minimum* time. You can lots of queueing delays and jitter most of the time, as long as you get one packet through unobstructed. Send enough probes and you'll make it. I did some similar work in 1992; see http://www.cs.columbia.edu/~smb/papers/netmeas.pdf for details. You couldn't repeat, today, exactly what I did then, because of the way pings are handled by modern routers, but I suspect one could find analogous schemes. To give one example of what I could tell -- and I was looking at the per-byte cost -- I was able to determine, from New Jersey, that a router outside Chicago was misconfigured; the site's backbone Ethernet should have been on the same card as the serial line (in the days of T-1 interfaces...), because copying the packet across the backplane introduceda noticeable per-byte delay. --Steven M. Bellovin, http://www.cs.columbia.edu/~smb
Current thread:
- Re: Geo location to IP mapping, (continued)
- Re: Geo location to IP mapping Jeff Rosowski (May 17)
- Re: Geo location to IP mapping Michael . Dillon (May 16)
- Re: Geo location to IP mapping Alain Hebert (May 15)
- Re: Geo location to IP mapping Valdis . Kletnieks (May 15)
- Re: Geo location to IP mapping Martin Hannigan (May 15)
- Message not available
- Message not available
- Re: Geo location to IP mapping Martin Hannigan (May 15)
- Re: Geo location to IP mapping sgorman1 (May 15)
- network triangulation (Re: Geo location to IP mapping) Edward B. DREGER (May 15)
- Re: Geo location to IP mapping Marshall Eubanks (May 15)
- Re: Geo location to IP mapping Steven M. Bellovin (May 15)
- Re: Geo location to IP mapping sgorman1 (May 16)
- Re: Geo location to IP mapping Charles Cala (May 16)
- Re: Geo location to IP mapping Marshall Eubanks (May 16)
- Re: Geo location to IP mapping Charles Cala (May 16)
- Re: Geo location to IP mapping Kevin Pawloski (May 15)
- Re: Geo location to IP mapping Michael . Dillon (May 16)
- Re: Geo location to IP mapping Edward B. DREGER (May 16)