The MPLS WG Archive

[Curtis Villamizar <curtis@workhorse.fictitious.org>]

In message <20001219133040.A3110@layer8.net>, Ben Black writes:
> On Tue, Dec 19, 2000 at 04:06:36PM -0500, Curtis Villamizar wrote:
> 
> > If the L3PID is IPv4, it is perfectly legitimate to send TTL expired
> > ICMP if TTL expires.  It is equally legitimate to ignore the L3PID and
> > not generate ICMP, or disable TTL decrement at all but the egress for
> > TE tunnels (where no loop is ever possible).  LSR that don't generate
> > ICMP are simply traceroute unfriendly and the path will pick up again
> > as soon as the TTL is large enough to reach the egress of the LSP.
> > 
> > If the L3PID is not IPv4 (for example MPLS) then an LSR should not try
> > to guess the type of payload.  Providers who want to retain
> > functionality that is only available if the L3PID is known will have
> > to set up TE hierarchical tunnels for IPv4 only and other hierarchical
> > tunnels to carry "anything else".  This would be true of hierarchical
> > tunnels for specific diff-serv CT values so this is no surprise.
> > 
> > The text is therefore fine as is.  Perhaps some minor clarification
> > can be made, but it does not make sense to remove this.
> > 
> 
> Then I propose we add text for ATM, Frame Relay, Circuit Emulation, ...
> 
> Ben


Ben,

ATM, Frame Relay, Circuit Emulation are clearly second class citizens.
Besides the fact that this is the IETF, these are supported mostly to
transition legacy services (whose market is growing very slowly, flat,
or shrinking in most providers according to their quarterly
statements.  When it goes negative, switched services stop getting
reported separately).

The initial and major use of MPLS was assumed to be IPv4.  For quite a
long time it was the exclusive use of MPLS in practice.  That
assumption is still correct today.  Some consideration of IPv4 in the
base MPLS documents is perfectly fine as long as it does not impact
the ability to support other L3PIDs.

It is perfectly fine to specify optional treatment for other L3PIDs in
separate documents if it made sense to support some form of special
treatment.  The encapsulation documents would be a good place to do
this.  If you really wanted to specify a feature such as setting FECN
or some other L3PID specific action, you could do so and see if there
is enough demand for the feature that anyone implements it.

Curtis