Long hops on international paths

Mon Jan 17 19:00:30 UTC 2022

Hello Nick,

I've added my collaborators to this reply - Esteban can comment on your observation re. Telia.

TTL is decremented on the paths we're analyzing.  What we're curious about is why we're seeing a concentration of hops at a small number of routers that appear on international paths.  I expected that when we looked at paths between e.g., US-Asia, US-Europe, US-South America (considering measurements from Ark nodes doing traceroutes to/from those locations), we would see the first instances of routers located the US along the west coast, east coast and south coast respectively. We did not expect to see Chicago as a first hop location in the US and are wondering e.g., if large providers do this to simplify their operations.  Hopefully that makes sense.  Any further thoughts are appreciated.

Regards, PB
________________________________
From: Nick Hilliard <nick at foobar.org>
Sent: Monday, January 17, 2022 12:36 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

PAUL R BARFORD wrote on 17/01/2022 18:02:
> For example, there is a router operated by Telia (AS1299) in Chicago
> that has a high concentration of such links.

this doesn't appear to match 1299's public network topology:

https://www.teliacarrier.com/our-network.html

Is ttl decrement disabled on the test paths you're measuring?

Broadly speaking, if you have a point-to-point link from one location to
another (or parallel set of links with a common failure path, e.g. waves
on a specific fibre path), there's a single router at each end.

Nick
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