Subject: [PWE3] Mandatory Control Word

From: Stewart Bryant <[email-masked]>
Date: Tue, 26 Oct 2010 18:23:35 +0100

From

draft-delregno-pwe3-mandatory-control-word/

=======
2.  Mandatory Control Word

    The Control Word SHALL be mandatory for all PWE3 encapsulations.  The
    use of the sequence number remains OPTIONAL.

    As a result of the Control Word being Mandatory, all implementations
    of the PWE3 encapsulations SHALL follow Section 6.1 of [RFC4447]
    wherein the "PWs MUST have c=1".  This requirement SHALL remain until
    such time, if ever, RFC4447 is superceded and the support for Control
    Word negotiation is removed as a result of this mandate.

======

Given the reality of network deployments I do not see how we can
talk about removing the requirement to negotiate the CW in any
realistic time frame.

It's fine to require the CW for all new PW types, and it's
probably OK to RECOMMEND operation with the CW, but it's
unrealistic to remove the option given the extent of the deployed
systems.

- Stewart

---

From: Thomas Nadeau <[email-masked]>
Date: Tue, 26 Oct 2010 13:41:43 -0400

Is this your personal opinion speaking as a vendor with lots of said equipment, or as an AD?

	--Tom

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---

From: "Shah, Himanshu" <[email-masked]>
Date: Tue, 26 Oct 2010 14:35:49 -0400

I do kind of agree with Stuart's assessment, AD or not... :-)

IMHO,
/himanshu

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Thomas Nadeau
Sent: Tuesday, October 26, 2010 1:42 PM
To: [email-masked]
Cc: pwe3
Subject: Re: [PWE3] Mandatory Control Word

	Is this your personal opinion speaking as a vendor with lots of
said equipment, or as an AD?

	--Tom

---

From: Ignacio Goyret <[email-masked]>
Date: Tue, 26 Oct 2010 13:36:04 -0700

+1

At 02:35 PM 10/26/2010 -0400, Shah, Himanshu wrote:
>From: Thomas Nadeau

---

From: Eric Gray <[email-masked]>
Date: Wed, 27 Oct 2010 02:55:16 -0400

Stewart,

	I agree with your suggested limitations to new PW types
and suggestion to recommend its use for existing PW types.

	However, the observation about deployed systems - when
taken together with what appears to be a growing impression
that use of the control word with all PW types may be a good 
idea - seems to argue that we would (eventually) need a BCP
that specifies use of the control word, and possibly we may
even have to publish a "non-use of PW control word considered 
dangerous" RFC.

	I don't see a way to avoid this, assuming that is where
we are headed, but it might be good to be clear on whether or
not that _is_ where we are headed.

	It also causes me to wonder if there are implementations
deployed in the field where use of the control word is not a
configurable capability.  Certainly, if deployed equipment is
all capable of being configured to always use control words,
then it is not unrealistic to suggest that configuring things
that way would simplify future implementations.

--
Eric

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of Stewart Bryant
Sent: Tuesday, October 26, 2010 1:24 PM
To: pwe3
Subject: [PWE3] Mandatory Control Word

From

=======

======

- Stewart

---

From: Stewart Bryant <[email-masked]>
Date: Wed, 27 Oct 2010 13:38:17 +0100

> 	Is this your personal opinion speaking as a vendor with lots of said equipment, or as an AD?
Assuming a Lynn Truss comma after "speaking".

The first and the last.

I personally think that we should not strand legacy systems. Widely 
deployed designs should only die at the end of their "natural" life.

As an AD I think that I have a duty of care to the Internet to make sure 
that we design our technology such that we ensure that we have migration 
paths rather than flag days.

Stewart

-- 
For corporate legal information go to:

http://www.cisco.com/web/about/doing_business/legal/cri/index.html

---

From: "Delregno, Christopher N (Nick DelRegno)" <[email-masked]>
Date: Wed, 27 Oct 2010 16:19:27 +0000

So, maybe it is not clear in the draft.  Let me see if I can clarify.

The aim of the draft is making the Control Word mandatory.  If there is
consensus with this approach I would ultimately see an RFC needed to
update the existing encapsulations to make CW mandatory.  For legacy
equipment which may never support such, they can adhere to the original
RFCs.  For these, preferably, they would also adhere to our VCCV
Mandatory Features draft to ensure interoperability of the control
channel in the absence of the Control Word mandate.

The second paragraph below is an aside.  At some point in time (note no
time frame given or even suggested, e.g. "if ever"), when all
encapsulations support the mandatory nature of the Control Word, the
need to negotiate such is obviated.  It can certainly be retained if
desired for the support of legacy or posterity, and therefore RFC4447
would never superceded.

Thanks,
Nick

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Stewart Bryant
Sent: Tuesday, October 26, 2010 12:24 PM
To: pwe3
Subject: [PWE3] Mandatory Control Word

From

=======

    The Control Word SHALL be mandatory for all PWE3 encapsulations.
The
    use of the sequence number remains OPTIONAL.

    As a result of the Control Word being Mandatory, all implementations
    of the PWE3 encapsulations SHALL follow Section 6.1 of [RFC4447]
    wherein the "PWs MUST have c=1".  This requirement SHALL remain
until
    such time, if ever, RFC4447 is superceded and the support for
Control
    Word negotiation is removed as a result of this mandate.

======

Given the reality of network deployments I do not see how we can talk
about removing the requirement to negotiate the CW in any realistic time
frame.

It's fine to require the CW for all new PW types, and it's probably OK
to RECOMMEND operation with the CW, but it's unrealistic to remove the
option given the extent of the deployed systems.

- Stewart

---

From: Thomas Nadeau <[email-masked]>
Date: Wed, 27 Oct 2010 13:28:53 -0400

Eric,

    What you surmise below is PRECISELY the point that Nick/I/others are making.
It is clear that in the large majority of deployments, the use of the CW *is*
the typical configuration. The only real non-use is with ATM PWs to apparently
"save bandwidth", but the real issue is to keep old equipment working. There
is no argument that we do not want to obviate older equipment, but what we
want is going forward to be doing the right thing for interoperability.
 
     The other observation we've made is that the myriad of options 
available to VCCV result in serious interoperability issues. These
different modes are available largely due to not making the CW 
mandatory (as well as the bailing-wire and bubble gum approach we
originally took to encapsulating different PW types).  
 
     The road to interop is simplification.  All we are proposing is:
 
     a) any protocols/documents in PWE3 that are not RFC at present, be required
          to use the CW.
 
     b) any existing protocols in PWE3 and future ones be required to use the CW 
when going to proposed standard status. 
 
     c) adoption of the negotiation of the CW status based on the draft that we proposed       
in the interim to aid in more automatic interop for operators.

	--Tom

---

From: Giles Heron <[email-masked]>
Date: Wed, 27 Oct 2010 20:34:44 +0100

Is that correct?  I'm pretty sure that most Ethernet PW deployments don't
use a CW (none of the Ethernet PWs I configured ever used a CW, but to be
fair that was a few years ago...)

For Ethernet there are no L2 flags, or minimum length issues, so the main
reasons for a CW would seem to be for VCCV (for which there are other
encapsulation options) and ECMP (which is only an issue in some networks).

Oh, from reading the draft you state that FR Port Mode, PPP, and HDLC all
have the same encap.  That's not strictly true.  For PPP mode you remove the
HDLC address/control fields (if present - remember that PPP can run over
non-HDLC media).

Giles

---

From: Ben Niven-Jenkins <[email-masked]>
Date: Thu, 28 Oct 2010 12:54:43 +0100

> encapsulation options) and ECMP (which is only an issue in some networks).

FWIW none of BT's Eth PWs use control word - they spent a long time talking about introducing them for VCCV but a combination of migration pain & scaling issues meant it never got past talking about it.

Ben

---

From: Greg Mirsky <[email-masked]>
Date: Thu, 28 Oct 2010 10:44:27 -0700

Dear Tom,
you definitely are aware of proposal to update RFC 5586 and allow use
of GAL in MPLS-TP PWs. I believe that this proposal is directly
affects RFC 5085 PW VCCV as it adds another VCCV Control Channel type.
If this proposal adopted it, in my view, will affect PW VCCV
interoperability that must be reflected in Mandatory Features of VCCV
Implementations. I see the proposal to make use of PW CW mandatory
(perhaps not "mandatory" but "preferred" or "default" behavior) as
alternative to extension of GAL, not complimentary or orthogonal. I
think that the PWE3 WG may choose one that will minimize operational
impact while restoring consistency in MPLS PW OAM (if only in some
part).

Regards,
Greg