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

Masataka Ohta mohta at necom830.hpcl.titech.ac.jp
Sat Jun 20 13:39:04 UTC 2020

Randy Bush wrote:

>>>> MPLS was since day one proposed as enabler for services originally
>>>> L3VPNs and RSVP-TE.
>>> MPLS day one was mike o'dell wanting to move his city/city traffic
>>> matrix from ATM to tag switching and open cascade's hold on tags.
>> And IIRC, Tag switching day one was Cisco overreacting to Ipsilon.
> i had not thought of it as overreacting; more embrace and devour.  mo
> and yakov, aided and abetted by sob and other ietf illuminati, helped
> cisco take the ball away from Ipsilon, Force10, ...

Ipsilon was hopeless because, as Yakov correctly pointed out, flow
driven approach to automatically detect flows does not scale.

The problem of MPLS, however, is that, it must also be flow driven,
because detailed route information at the destination is necessary
to prepare nested labels at the source, which costs a lot and should
be attempted only for detected flows.

 > there is the argument that switching MPLS is faster than IP; when the
 > pressure points i see are more at routing (BGP/LDP/RSVP/whatever),
 > recovery, and convergence.

Routing table at IPv4 backbone today needs at most 16M entries to be
looked up by simple SRAM, which is as fast as MPLS look up, which is
one of a reason why we should obsolete IPv6.

Though resource reserved flows need their own routing table entries,
they should be charged proportional to duration of the reservation,
which can scale to afford the cost to have the entries.

						Masataka Ohta

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