Re: Two Drafts for Resilience of Control Plane

["Igor Bryskin" <ibryskin@movaz.com>]

Dimitri,
> igor - my two cents
>
> RSVP over time has progressively borrowed mechanisms from "hard-state"
> protocols, explicit deletion using PathTear is most noticeable and
> initial example of this evolution !
>
> but in any case, RSVP still relies is on idem-potent soft-states that
> are flushed when not refreshed after certain time interval (or self-
> maintained if previously negotiated) this prevents orphans in the
> network (so unused resources) and provides for resilience - hence there
> is by no means a need to introduce an additional protocol mechanism to
> trigger or not such event via the "control plane" -

Refreshes are useful mechanism but only between neighbors that maintain
Hello communication. In this case the absence of Path refreshes is as good
indication that data plane must be destroyed as received PathTear message.
However, when a controller does not receive Path refreshes from a neighbor
it does not have any control plane communication with, it can assume neither
a problem in the data plane nor intention to destroy it. Hence, as it was
specified in RFC3471, it *must* maintain both control and data plane states
throughout the failure.

Igor

>
> btw, the paragraph you mention in RFC3471 does not say "soft state
> protocols do not work well for non-packet environments" this is your
> interpretation;
>
> ps: you are still free to make use of RFC3472 in case (as you were
> apparently looking for something else ;-)
>
> Igor Bryskin wrote:
> > John,
> >
> >
> >
> >>>States are supposed to be destroyed on explicit signalling
> >>>message (e.g. PathTear or PathErr with the state removal
> >>>flag), but not because of the absence of refreshes.
> >>>
> >
> > [JD]
> >
> > Igor,
> >
> > Just to be clear, we are talking about RSVP here, and RSVP *is* a soft
> > state protocol.  Can you point to any RFC that supports your statements
> > above?
> >
> > IB>> Oh, come on, John. You sound like you've been yourself in a dormant
> > state for a while :=). We've gone a long way since RFC2205. In RFC3471,
for
> > example, there is a discussion why GMPLS is needed and how is it
different
> > from MPLS. One of the differences is the fact that soft state protocols
do
> > not work well for non-packet environments. Here is from the RDC3471:
> >
> >
> >
> > 9.2. Fault Handling    There are two new faults that must be handled
when
> > the control   channel is independent of the data channel.  In the first,
> > there is a   link or other type of failure that limits the ability of
> > neighboring   nodes to pass control messages.  In this situation,
> > neighboring nodes   are unable to exchange control messages for a period
of
> > time.  Once   communication is restored the underlying signaling
protocol
> > must   indicate that the nodes have maintained their state through the
> > failure..
> >
> > What is more important is the reality of life: The customers simply say
that
> > you cannot destroy a user service (or even force any traffic hits) just
> > because you have a problem in the control plane. If this does not fit
your
> > soft-state paradigm, than "harden" your protocols or flash them down the
> > toilet and come with something else if you want our business. After all,
if
> > we provision the services via NMS, we do not have to destroy the
services if
> > we have problems in the management network. It is that simple.
> >
> >
> >
> > Igor
> >
> >
> >
> >
> >
> >
> >
> > .
> >