Subject: [PWE3] I-D Action: draft-ietf-pwe3-redundancy-04.txt

From: [email-masked]
Date: Fri, 08 Jul 2011 05:44:22 -0700

A New Internet-Draft is available from the on-line Internet-Drafts directories. This draft is a work item of the Pseudowire Emulation Edge to Edge Working Group of the IETF.

	Title           : Pseudowire Redundancy
	Author(s)       : Praveen Muley
                          Mustapha Aissaoui
                          Matthew Bocci
	Filename        : draft-ietf-pwe3-redundancy-04.txt
	Pages           : 17
	Date            : 2011-07-08

   This document describes a framework comprised of a number of
   scenarios and associated requirements for pseudowire (PW)
   redundancy. A set of redundant PWs is configured between provider
   edge (PE) nodes in single segment PW applications, or between
   Terminating PE nodes in Multi-Segment PW applications. In order for
   the PE/T-PE nodes to indicate the preferred PW to use for forwarding
   PW packets to one another, a new PW status is required to indicate
   the preferential forwarding status of active or standby for each PW
   in the redundancy set.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ietf-pwe3-redundancy-04.txt

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

This Internet-Draft can be retrieved at:
ftp://ftp.ietf.org/internet-drafts/draft-ietf-pwe3-redundancy-04.txt

---

From: "Daniel Cohn" <[email-masked]>
Date: Thu, 21 Jul 2011 12:46:57 +0300

Hi authors,

draft-ietf-pwe3-redundancy-bit uses the PW operational status as an
input to the active PW selection logic. In this draft, the operational
status is taken from the (local and remote) PW status bits.

The draft defines "UP PW" (eligible to become active PW) as "PW which
... and is not in any of the PW defect states specified in [2]". So the
PW operational status, in the context of this draft, takes into account
local/remote AC statuses.

On the other hand, the standard PW MIB (RFC 5601) explicitly defines the
PW operational status as not considering the AC statuses - "This object
indicates the operational status of the PW; it does not reflect the
status of the Customer Edge (CE) bound interface...". 

If my understanding is correct, then I believe there is a terminology
conflict that should be resolved.

Am I missing something? Please comment.

Regards,

Daniel

---

From: "Aissaoui, Mustapha (Mustapha)" <[email-masked]>
Date: Wed, 27 Jul 2011 17:03:55 -0500

Hi Daniel,
the definition for the PW UP state in the terminology section (Section 3) was meant to cover only the status bits related to defects of the PW, i.e.,

0x00000001 -  Pseudowire Not Forwarding
0x00000008 -  Local PSN-facing PW (ingress) Receive Fault
0x00000010 -  Local PSN-facing PW (egress) Transmit Fault
I will clarify this in the next version.

Having said that, the selection of the active PW in Section 5.1 may need to be updated to optionally consider remote AC state as advertized in the received status bits from the peer. I was made aware of some deployments where the failure of a remote AC was not translated into a standby bit advertisement. Consider the scenario in Figure 15-1 where PE1 and PE3 did not synchronize the active/standby AC state. Thus both PE1 and PE3 advertized PW active status bit and PE2 choose PW1 based on precedence. When the active AC went down, PE1 generated a status bit to notify PE2 of AC down but PE2 did not switch to PW2 because the AC state is not part of the selection criteria in Section 5.1.

Regards,
Mustapha.

________________________________
From: [email-masked] [mailto:[email-masked]] On Behalf Of Daniel Cohn
Sent: Thursday, July 21, 2011 5:47 AM
To: [email-masked]
Subject: [PWE3] Operational status definition in draft-ietf-pwe3-redundancy-bit

Hi authors,

draft-ietf-pwe3-redundancy-bit uses the PW operational status as an input to the active PW selection logic. In this draft, the operational status is taken from the (local and remote) PW status bits.

The draft defines "UP PW" (eligible to become active PW) as "PW which ... and is not in any of the PW defect states specified in [2]". So the PW operational status, in the context of this draft, takes into account local/remote AC statuses.

On the other hand, the standard PW MIB (RFC 5601) explicitly defines the PW operational status as not considering the AC statuses - "This object indicates the operational status of the PW; it does not reflect the status of the Customer Edge (CE) bound interface...".

If my understanding is correct, then I believe there is a terminology conflict that should be resolved.

Regards,

Daniel

---

From: "Daniel Cohn" <[email-masked]>
Date: Thu, 28 Jul 2011 01:20:49 +0300

Hi Mustapha,

Actually I thought, and agreed, that selection must take AC status into
account, as per the "UP PW" definitions in the current draft. 

As you wrote, AC down should be a trigger for PW protection, seeing as
the AC is an integral part of the PW. Figure 15-1 is an excellent
example of this, and some additional, similar examples can also be
presented.

So, may I suggest you leave the UP/DOWN PW definition as they are, and
instead replace the loaded "operational state" terms by something
unambiguous like for example "UP/DOWN state"? This will avoid
misunderstanding and support scenarios like the one in figure 15-1.

Regards,

Daniel

From: Aissaoui, Mustapha (Mustapha)
[mailto:[email-masked]] 
Sent: Wednesday, July 27, 2011 6:04 PM
To: Daniel Cohn; [email-masked]
Subject: RE: [PWE3] Operational status definition
indraft-ietf-pwe3-redundancy-bit

Hi Daniel,

the definition for the PW UP state in the terminology section (Section
3) was meant to cover only the status bits related to defects of the PW,
i.e.,

Having said that, the selection of the active PW in Section 5.1 may need
to be updated to optionally consider remote AC state as advertized in
the received status bits from the peer. I was made aware of some
deployments where the failure of a remote AC was not translated into a
standby bit advertisement. Consider the scenario in Figure 15-1 where
PE1 and PE3 did not synchronize the active/standby AC state. Thus both
PE1 and PE3 advertized PW active status bit and PE2 choose PW1 based on
precedence. When the active AC went down, PE1 generated a status bit to
notify PE2 of AC down but PE2 did not switch to PW2 because the AC state
is not part of the selection criteria in Section 5.1.

Regards,

Mustapha.

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Daniel Cohn
Sent: Thursday, July 21, 2011 5:47 AM
To: [email-masked]
Subject: [PWE3] Operational status definition in
draft-ietf-pwe3-redundancy-bit

Hi authors,

Regards,

Daniel