Long hops on international paths

Christopher Morrow morrowc.lists at gmail.com
Mon Jan 17 23:13:45 UTC 2022

On Mon, Jan 17, 2022 at 5:31 PM PAUL R BARFORD <pb at cs.wisc.edu> wrote:

> Dear Pengxiong,
> Thanks for your questions:
>    1. We are using CAIDA’s Internet Topology Data Kit (ITDK) that uses
>    the MIDAR alias resolution method to infer IP addresses assigned to the
>    same router.
>    2. We understand the concerns about IP geolocation.  Interfaces of the
>    router in question are assigned similar domain names e.g., “
>    chi-b2-link.ip.twelve99.net” ( We also used CAIDA’s
>    ITDK, which provides geolocation information, and indicates that this
>    router is located in Chicago.  We cross-reference with Maxmind where
>    possible.  In this particular case, there is the telltale in the use of
>    "chi" in the domain name.
>    3.
I think nick's point about ttl expiry and missing some context on
topology still stands.
I'd be that the paths between 2 continents do not actually land in
chicago... that you're seeing (or not seeing) missing hops between the
coast(s) and chicago inside 1299's network in the US.

>    1.
> Hope that helps.
> Regards, PB
> ------------------------------
> *From:* Pengxiong Zhu <pzhu011 at ucr.edu>
> *Sent:* Monday, January 17, 2022 3:23 PM
> *To:* PAUL R BARFORD <pb at cs.wisc.edu>
> *Cc:* nanog at nanog.org <nanog at nanog.org>
> *Subject:* Re: Long hops on international paths
> Hi Paul,
> Just curious. How do you determine they are the same routers? Is it based
> on IP address or MAC addresses? Or using CAIDA’s router alias database?
> Also how do you draw the conclusion that the AS1299 router is indeed in
> Chicago? IP-geolocation based on rDNS is not always accurate though.
> Pengxiong
> On Mon, Jan 17, 2022 at 10:03 AM PAUL R BARFORD <pb at cs.wisc.edu> wrote:
> Hello,
> I am a researcher at the University of Wisconsin.  My colleagues at
> Northwestern University and I are studying international Internet
> connectivity and would appreciate your perspective on a recent finding.
> We're using traceroute data from CAIDA's Ark project for our work.  We've observed
> that many international links (i.e., a single hop on an end-to-end path
> that connects two countries where end points on the hop are identified via
> rDNS) tend to originate/terminate at the same routers.  Said another way,
> we are observing a relatively small set of routers in different countries
> tend to have a majority of the international connections - this is
> especially the case for hops that terminate in the US.  For example,
> there is a router operated by Telia (AS1299) in Chicago that has a high
> concentration of such links.  We were a bit surprised by this finding since
> even though it makes sense that the set of providers is relatively small
> (i.e., those that offer global connectivity), we assumed that the set of
> routers that used for international connectivity within any one country
> would tend to be more widely distributed (at least with respect to how they
> appear in traceroute data - MPLS notwithstanding).
> We're interested in whether or not this is indeed standard practice and if
> so, the cost/benefit for configuring international connectivity in this
> way?
> Any thoughts or insights you might have would be greatly appreciated -
> off-list responses are welcome.
> Thank you.
> Regards, PB
> Paul Barford
> University of Wisconsin - Madison
> --
> Regards,
> Pengxiong Zhu
> Department of Computer Science and Engineering
> University of California, Riverside
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