GRH Longest Distance Routing

Jeroen Massar jeroen at
Sun Apr 1 06:06:48 CEST 2007

As per:

Sunday, April 1st - GRH: Longest Distance Routing

In networking commonly packets will take the shortest path from A to B,
this is as it says: Shortest Path Routing. Usually this calculation is
done on the AS-PATH, the shortest AS-PATH that is the oldest for a
particular destination gives the best possible route, and thus that is
chosen. This is used in BGP and as such for the Internet. GRH[1]
monitors this Internet for the IPv6 BGP tables and sometimes one notices
that a path is quite long as shown in the AS-PATH for that prefix. The
length of such an AS-PATH doesn't tell much about the actual physical
distance and it unfortunately still seems to happen that AS-PATH's are
chosen that go a couple times around the world. To see how long these
actually get, especially for this day we release a new extension to GRH:
Longest Distance Routing.

Check this archived snapshot of the full routing table[2] [4 MiB] which
has the view from which we took the below results. The winners for the
first annual Longest Distance Routing contest are:

2001:256::/32 24541 30071 2018 6149 11537 10764 23911 4538 23910 18011
at 53512 km
flowing through Australia, US, Africa, US, and China. Unfortunately,
this one is not correct, TENET has a router in NY, and though their
network is African these packets are not being shipped to Africa and
back to the US again.

2001:200:a000::/35 26943 4436 3549 6939, 2516 7660, 22388 11537, 2500 at
45056 km
2001:200:a000::/35 19255, 26943, 4436 3549 6939, 2516 7660, 22388 11537,
2500 at 45056 km
going through The Netherlands, US, Japan, US, and Japan.
These two take the internal network of, so these two doesn't
count either, although they are getting pretty long!

But these though are most likely pretty accurate:
2001:200:a000::/35 25441, 3257, 3549, 6939, 2516 7660, 22388 11537, 2500
at 40760 km
flowing through Ireland, Germany, Netherlands, US, Japan, US and Japan.
2001:200:a000::/35 1836, 3549, 6939, 2516 7660, 22388 11537, 2500 at
39500 km
flowing through Switzerland, Netherlands, US, Japan, US, and Japan.

We hope this shows that AS-PATH lengths are far from useful in some
cases for determining the shortest path. We also hope that certain
operators who do this long-distant transiting and full route-swap,
consider not doing this for the sake of the IPv6 Internet. Thank you for
your attention, and till next years edition of Longest Distance Routing!

Note: This feature is from now on available throughout GRH: Happy hunting!
Location data is based on the capital of the country in which the ASN
resides. The location information is taken from the CIA Factbook[3]

[1] GRH:
[2] Results:


And yes, I am aware that some ASN's are not correctly represented in
which countries they are. Country information is taken from aut-num
objects when that is available (APNIC&JPNIC seem to have that) and from
inet6num objects mapped to route6 objects. If an ASN is thus without
country it has neither of those. The algorithm works by ignoring ASN's
which are in the same country and ignoring ASN's marked as 'int' aka
International, which takes out the larger transits, I assume that they
are present in the country where they pick up and drop the traffic, and
the distance is taken from those two countries, not the actual countries
in between. The distance is further measured in a curve around the globe
between the capitals of the country, as based on data from the CIA
factbook (now they know what that weird 'NeedCoords' user agent is ;).

If someone has a better source for getting ASN->Country information or
other creative comments with valid arguments, then of course don't
hesitate to give a shout.


PS: Happy 1st of April! Don't get fooled too much :)

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