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

Robert Raszuk robert at raszuk.net
Sun Jun 21 13:24:30 UTC 2020

It is destination based flat routing distributed 100% before any data
packet within each layer - yes. But layers are decoupled so in a sense this
is what defines a hierarchy overall.

So transport is using MPLS LSPs most often hosts IGP routes are matched
with LDP FECs and flooded everywhere in spite of RFC 5283 at least allowing
to aggregate IGP.

Then say L2VPNs or L3VPNs with their own choice of routing protocols are in
turn distributing reachability for the customer sites. Those are service
routes linked to transport by BGP next hop(s).

Many thx,

On Sun, Jun 21, 2020 at 1:11 PM Masataka Ohta <
mohta at necom830.hpcl.titech.ac.jp> wrote:

> Robert Raszuk wrote:
> > MPLS LDP or L3VPNs was NEVER flow driven.
> >
> > Since day one till today it was and still is purely destination based.
> If information to create labels at or near sources to all the
> possible destinations is distributed in advance, may be. But
> it is effectively flat routing, or, in extreme cases, flat host
> routing.
> Or, if information to create labels to all the active destinations
> is supplied on demand, it is flow driven.
> On day one, Yakov said MPLS had scaled because of nested labels
> corresponding to routing hierarchy.
>                                                 Masataka Ohta
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