Looking forward to join the upcoming IXP chat, Bill!

All the best,

Frank

Frantisek (Frank) Borsik



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On Fri, Jan 19, 2024 at 8:26 AM Bill Woodcock via Nnagain <
nnagain@lists.bufferbloat.net> wrote:

>
>
> > On Jan 19, 2024, at 08:14, Sebastian Moeller <moeller0@gmx.de> wrote:
> >> On 18. Jan 2024, at 23:38, Bill Woodcock via Nnagain <
> nnagain@lists.bufferbloat.net> wrote:
> >> So, if one Internet user wants to talk to another Internet user,
> generally they hand off their packet to an Internet service provider, who
> takes it to an exchange, and hands it off to another Internet service
> provider, who delivers it to the second user.  When the second user wants
> to reply, the process is reversed, but the two Internet service providers
> may choose a different exchange for the hand-off: since each is
> economically incentivized to carry the traffic the shortest possible
> distance (to minimize cost, speed x distance = cost), the first ISP will
> always choose the IXP that’s nearest the first user, for the hand-off,
> leaving the second ISP a longer distance to carry the packet.  Then, when
> their situations are reversed, the second ISP will choose the IXP nearest
> the second user, leaving the first ISP to carry the packet a longer
> distance.
> >
> > I would propose a slight modification, "each is economically
> incentivized to carry the traffic the shortest possible distance" is not
> free of assumptions... namely that the shortest path is the cheapest path,
> which is not universally true.
>
> Correct.  That’s a simplification of a complex field where distance and
> cost are frequently intermingled, and routing decisions are typically based
> on latency, overridden by cost as a matter of policy.  However, in a
> simplified or idealized case, if speed is held constant, distance and cost
> scale together, so they are usually held to be interchangeable in
> decision-making in the general case.  Speed x distance = cost.
>
> > My personal take is "routing follows cost" that is it is money in the
> end that steers routing decisions
>
> Yes, exactly.
>
> The primary case in which routes follow a cost that differs from distance
> is in the preference for distant downstream transit over nearby peers, and
> distant peers over nearby upstream transit.  Though it’s uncommon in
> networks of small geographic scale, most global-scale networks do this, and
> it’s the cause of many routing problems and loops.
>
> > ...at least once we include paid peering...
>
> That’s a marketing euphemism for transit.
>
> > My ISP aggregates its customers in a handful of locations in Germany,
> Hamburg in my case while I actually live a bit closer to Frankfurt than
> Hamburg, so all traffic first goes to Hamburg even traffic to Frankfurt
> (resulting in a 500-600 Km detour), I assume they do this for economic
> reasons and not just out of spite ;)
>
> Essentially all mobile network operators do this.  It’s generally a matter
> of incompetence and lack of competition, rather than spite or economic
> reasons.
>
> > Now, maybe the important point is, this does not involve IXPs so might
> be an orange to the IXP apple?
>
> Yes, only indirectly.  Most of what you’re discussing involves non-optimal
> outbound IXP selection, one quarter of the round-trip path.  Very real
> issues, but not anything an IXP or receiving-side ISP can do much about
> without second-guessing routing decisions to an impractical degree.
>
>                                 -Bill
>
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