Subject: RE: [PWE3] BFD for MPLS PWs

From: "Busschbach, Peter B (Peter)" <[email-masked]>
Date: Fri, 18 Aug 2006 09:55:37 -0400

To move the discussion forward, let me follow up on my own question.

I believe that there is a broad concensus that insertion of AIS, as mandated by draft-ietf-pwe3-atm-encap-11, implies that the PE will NOT send an additional PW Status message to report the same defect.

RFC 4447 states "The PW status signaling procedures described in this section MUST be fully implemented." The document itself, however, specifies HOW to use PW Status signaling but is vague about WHEN to use PW Status signaling. The latter is addressed in the encapsulation drafts, such as atm-encap, and is fully defined in OAM-MAP (draft-ietf-pwe3-oam-msg-map-04).

The notion that RFC 4447 should be interpreted as a mandate to send a PW Status message for every single defect is an incorrect interpretation of the spirit of the standard, does not reflect WG concensus and, if implemented, would lead to inefficient implementations.

Therefore, I strongly disagree with the point of view that Tom and Luca have formulated regarding the use of BFD for both fault detection and status signaling. When this option is used, there is, IMO, no need to send PW Status messages. The current text of OAM-MAP is in line with this view.

Peter

> -----Original Message-----
> From: Busschbach, Peter B (Peter) [mailto:[email-masked]]
> Sent: Wednesday, August 16, 2006 4:40 PM
> To: 'Luca Martini'
> Cc: Swallow George; 'Thomas D. Nadeau'; Pignataro Carlos; Morrow
> Monique; pwe3 WG ((((((((E-mail)))))))); Danny McPherson; 
> Agarwal Rahul;
> Stewart (stbryant) Bryant
> Subject: RE: [PWE3] BFD for MPLS PWs
> 
> 
> Luca,
> 
> Section 7.4 of the ATM Encapsulation draft 
> (draft-ietf-pwe3-atm-encap-11.txt) mandates that upon LOS the 
> ingress PE inserts F4 AIS for every affected VPC. Is it your 
> opinion that because of RFC 4447 the ingress PE must send a 
> PW Status message in addition to F AIS insertion?
> 
> Peter
> 
> > -----Original Message-----
> > From: Luca Martini [mailto:[email-masked]]
> > Sent: Tuesday, August 15, 2006 6:29 PM
> > To: Busschbach, Peter B (Peter)
> > Cc: 'Thomas D. Nadeau'; Swallow George; Pignataro Carlos; Morrow
> > Monique; pwe3 WG ((((((((E-mail)))))))); Danny McPherson; 
> > Agarwal Rahul;
> > Stewart (stbryant) Bryant
> > Subject: Re: [PWE3] BFD for MPLS PWs
> > 
> > 
> > Busschbach, Peter B (Peter) wrote:
> > >
> > > In my opinion, the work on VCCV and OAM-MAP provides a 
> > further specification of RFC4447 and in fact overrules the 
> > requirement that LDP Status signaling must be used.
> > >
> > >
> > >   
> > Peter, 
> > We agreed a long time ago that the LDP status messaging was 
> > going to be mandatory , in fact people insisted I make it mandatory.
> > So I would have to say that the LDP status MUST always be 
> > used as mandated in RFC 4447, and the BFD status messaging is 
> > an optional, and , in my opinion, not a very useful option 
> > when LDP is in use.
> > 
> > Luca
> > 
> > 
> > > A minor comment on your email:
> > > I am not sure what you mean by the "de-facto status must 
> > always rely on LDP". Either you declare that that the PW is 
> > down when (1) BFD OR LSP indicate a PW failure, or (2) based 
> > only on the LDP status. In my mind "de-facto status" implies 
> > (2), whereas the beginning of your email says that (1) is the 
> > proposed procedure.
> > >
> > > Peter
> > >  
> > >
> > > _______________________________________________
> > > pwe3 mailing list
> > > [email-masked]
> > > https://www1.ietf.org/mailman/listinfo/pwe3
> > >   
> > 
> 
> _______________________________________________
> pwe3 mailing list
> [email-masked]
> https://www1.ietf.org/mailman/listinfo/pwe3
> 

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---

From: Luca Martini <[email-masked]>
Date: Fri, 18 Aug 2006 16:14:53 -0600

> I believe that there is a broad concensus that insertion of AIS, as mandated by draft-ietf-pwe3-atm-encap-11, implies that the PE will NOT send an additional PW Status message to report the same de…
Here I am assuming you mean insertion of an AIS alarm at the PE toward 
the local attachment circuit.
We should also send a status message with status "0x00000008 - Local 
PSN-facing PW (ingress) Receive Fault "  fault in this case.
Remember that the MPLS path might have gone down completely because 
somewhere a router was mis-configured , and can now only forward IP packets.
This message would be immediate , and much faster then any VCCV path 
fault detection scheme.

> RFC 4447 states "The PW status signaling procedures described in this section MUST be fully implemented." The document itself, however, specifies HOW to use PW Status signaling but is vague about W…
This is not my interpretation. When we say procedures described in this 
section MUST be fully implemented, implies that the protocol will send 
and receive status messages when appropriate. The trigger to send the 
status messages is attachment circuit specific, and therefore is  
described in the encapsulation drafts.
> The notion that RFC 4447 should be interpreted as a mandate to send a PW Status message for every single defect is an incorrect interpretation of the spirit of the standard, does not reflect WG con…
I disagree, and I have seen no indication that the WG interpreted the 
rfc4447 in this fashion.
> Therefore, I strongly disagree with the point of view that Tom and Luca have formulated regarding the use of BFD for both fault detection and status signaling. When this option is used, there is, I…
I would suggest that you look at the e-mail archive. If I remember 
correctly there were strong opinions about making the PW status messages 
mandatory.

The current text OAM-MAP needs to be changed.

Luca

---

From: "Yaakov Stein" <[email-masked]>
Date: Sun, 20 Aug 2006 11:29:12 +0200

I would like to fully agree with Peter.

I never understood the PW status messaging to be THE mandatory method
of communicating defect indications, rather I believed that the wording
about
it being implemented refered to requiring the receiver to understand
these messages.

In my opinion the mixing of OAM functionality (a user-plane function)
with the signaling protocol (a control plane function)
should only be done when there is no alternative,
e.g. VCCV is not supported.

Luca - can you give us a pointer to the thread where the WG
decided that the PW status messages were the defect reporting
mechanism of choice ?

Y(J)S

-----Original Message-----
From: Busschbach, Peter B (Peter) [mailto:[email-masked]] 
Sent: Friday, August 18, 2006 15:56
To: 'Luca Martini'
Cc: Swallow George; 'Thomas D. Nadeau'; Pignataro Carlos; Morrow
Monique; pwe3 WG ((((((((E-mail)))))))); Danny McPherson; Agarwal Rahul;
Stewart (stbryant) Bryant
Subject: RE: [PWE3] BFD for MPLS PWs

I believe that there is a broad concensus that insertion of AIS, as
mandated by draft-ietf-pwe3-atm-encap-11, implies that the PE will NOT
send an additional PW Status message to report the same defect.

RFC 4447 states "The PW status signaling procedures described in this
section MUST be fully implemented." The document itself, however,
specifies HOW to use PW Status signaling but is vague about WHEN to use
PW Status signaling. The latter is addressed in the encapsulation
drafts, such as atm-encap, and is fully defined in OAM-MAP
(draft-ietf-pwe3-oam-msg-map-04).

The notion that RFC 4447 should be interpreted as a mandate to send a PW
Status message for every single defect is an incorrect interpretation of
the spirit of the standard, does not reflect WG concensus and, if
implemented, would lead to inefficient implementations.

Therefore, I strongly disagree with the point of view that Tom and Luca
have formulated regarding the use of BFD for both fault detection and
status signaling. When this option is used, there is, IMO, no need to
send PW Status messages. The current text of OAM-MAP is in line with
this view.

Peter

---

From: "Andrew G. Malis" <[email-masked]>
Date: Tue, 22 Aug 2006 17:16:00 -0400

Without trying to unwind the 20 levels of this email thread, I think 
a key point is that Peter asserted (assuming I've followed this 
thread correctly) that there was strong WG consensus for only using 
BFD Status messages to signal AC and PW faults and that PW status 
signalling is redundant.  I don't see that consensus - for example, I 
happen to agree with Luca that there may be cases where only IP will 
be able to get through, and in those cases, PW status signaling has value.

I do agree that there has been an evolution of thinking over time in 
the WG (seeing as we originally started with just withdrawing PW 
labels in the original Martini draft), and what we probably need at 
this point is a single clear overview in one place of the OAM and 
status signaling functionality currently agreed upon in the WG.  Once 
we agree we have a clear consensus,  we can then make sure that the 
specific documents (encapsulations, OAM-MAP, VCCV, etc.) are 
consistent with that overview and with each other.

Cheers,
Andy

-----------

At 8/18/2006 16:14 -0600, Luca Martini wrote:
>>mandated by draft-ietf-pwe3-atm-encap-11, implies that the PE will 
>>NOT send an additional PW Status message to report the same defect.
>>
>>
>Here I am assuming you mean insertion of an AIS alarm at the PE 
>toward the local attachment circuit.
>>RFC 4447 states "The PW status signaling procedures described in 
>>this section MUST be fully implemented." The document itself, 
>>however, specifies HOW to use PW Status signaling but is vague 
>>about WHEN to use PW Status signaling. The latter is addressed in 
>>the encapsulation drafts, such as atm-encap, and is fully defined 
>>in OAM-MAP (draft-ietf-pwe3-oam-msg-map-04).
>>
>>
>This is not my interpretation. When we say procedures described in 
>this section MUST be fully implemented, implies that the protocol 
>will send and receive status messages when appropriate. The trigger 
>to send the status messages is attachment circuit specific, and therefore is
>>The notion that RFC 4447 should be interpreted as a mandate to send 
>>a PW Status message for every single defect is an incorrect 
>>interpretation of the spirit of the standard, does not reflect WG 
>>concensus and, if implemented, would lead to inefficient implementations.
>>
>>
>I disagree, and I have seen no indication that the WG interpreted 
>the rfc4447 in this fashion.
>>Therefore, I strongly disagree with the point of view that Tom and 
>>Luca have formulated regarding the use of BFD for both fault 
>>detection and status signaling. When this option is used, there is, 
>>IMO, no need to send PW Status messages. The current text of 
>>OAM-MAP is in line with this view.
>>
>>
>correctly there were strong opinions about making the PW status 
>messages mandatory.
>
>>>opinion that because of RFC 4447 the ingress PE must send a PW 
>>>Status message in addition to F AIS insertion?
>>>
>>>Peter
>>>
>>>
>>>>Peter, We agreed a long time ago that the LDP status messaging 
>>>>was going to be mandatory , in fact people insisted I make it mandatory.
>>>>So I would have to say that the LDP status MUST always be used as 
>>>>mandated in RFC 4447, and the BFD status messaging is an 
>>>>optional, and , in my opinion, not a very useful option when LDP is in use.
>>>>
>>>>Luca
>>>>
>>>>
>>>>
>>>>always rely on LDP". Either you declare that that the PW is down 
>>>>when (1) BFD OR LSP indicate a PW failure, or (2) based only on 
>>>>the LDP status. In my mind "de-facto status" implies (2), whereas 
>>>>the beginning of your email says that (1) is the proposed procedure.
>>>>
>>>>>Peter
>>>>>