why am i in this handbasket? (was Devil's Advocate - Segment Routing, Why?)

Mark Tinka mark.tinka at seacom.mu
Mon Jun 22 13:51:12 UTC 2020

On 22/Jun/20 15:08, Masataka Ohta wrote:

> The requirement from the E2E principle is that routers should be
> dumb and hosts should be clever or the entire system do not.
> scale reliably.

And yet in the PTT world, it was the other way around. Clever switching
and dumb telephone boxes. How things have since evened out.

I can understand the concern about making the network smart. But even a
smart network is not as smart as a host. My laptop can do a lot of
things more cleverly than any of the routers in my network. It just
can't do them at scale, consistently, for a bunch of users. So the
responsibility gets to be shared, with the number of users being served
diminishing as you enter and exit the edge of the network.

It's probably not yet an ideal networking paradigm, but it's the one we
have now that is a reasonably fair compromise.

> In this case, such clever router can ever exist only near the
> destination unless very detailed routing information is flooded
> all over the network to all the possible sources.

I will admit that bloating router code over recent years to become
terribly smart (CGN, Acceleration, DoS mitigation, VPN's, SD-WAN, IDS,
Video Monitoring, e.t.c.) can become a run away problem. I've often
joked that with all the things being thrown into BGP, we may just see it
carrying DNS too, hehe.

Personally, the level of intelligence we have in routers now beyond
being just Layer 1, 2, 3 - and maybe 4 - crunching machines is just as
far as I'm willing to go. If, like me, you keep pushing back on vendors
trying to make your routers also clean your dishes, they'll take the
hint and stop bloating the code.

Are MPLS/VPN's overly clever? I think so. But considering the pay-off
and how much worse it could get, I'm willing to accept that.

> A router can't be clever on something, unless it is provided
> with very detailed information on all the possible destinations,
> which needs a lot of routing traffic making entire system not
> to scale.

Well, if you can propose a better way to locate hosts on a global
network not owned by anyone, in a connectionless manner, I'm sure we'd
all be interested.


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