Subject: RE: Comments on draft-key-l2vpn-vpls-etree-02

From: "Delregno, Christopher N (Nick DelRegno)" <[email-masked]>
Date: Tue, 04 May 2010 16:34:17 +0000

Ray:

Sorry for the delay...been on vacation.

Thanks for the clarification.  I missed the part of Root-only ACs part
in section 5.3.  Makes sense.  I'd prefer a bit of clarification in the
5.3 text.  It is not that only root ACs can be connected to the PE.  It
is that leaf ACs MUST NOT be connected to the PE.  The other PEs will
assume that all ACs on the PE which doesn't support the extension
(whether CW or L-Bit), are Root-only ACs, whether that is the case or
not.

I haven't had a chance to review the ETREE Requirements draft yet, but
it is on my to-do list...

Thanks,
Nick

-----Original Message-----
From: Raymond Key [mailto:[email-masked]] 
Sent: Friday, April 23, 2010 8:39 PM
To: Delregno, Christopher N (Nick DelRegno)
Cc: [email-masked]
Subject: Comments on draft-key-l2vpn-vpls-etree-02

Hi Nick,

Thanks for your comment.

Quote from your email, "However, if we are relying on CW to indicate
leaf/root and the targeted PE doesn't support CW, then the ETREE model
breaks as I can no longer determine leaf/root and drop/forward traffic
accordingly."

There may be some confusion here. When the targeted PE doesn't support
CW, it also implies the targeted PE doesn't support the extension
specified in this draft (see section 4.2, "A PE MUST be capable of
sending and receiving the Control Word on Ethernet PW") and hence the
targeted PE has only Root ACs. This is a backward compatibility scenario
and does not result in any problem.

Backward compatibility issues are discussed in section 5 in the draft. 
(http://tools.ietf.org/html/draft-key-l2vpn-vpls-etree-02#section-5)
Some paragraphs are extracted below.

(5.3. Additional Action in Data Forwarding)

For backward compatibility reason, a PE not supporting the extension
specified in this document can participate in an E-Tree construct, but
only Root ACs can be connected to such PE.

Lack of Control Word L-bit per-payload signaling between a PE supporting
the extension specified in this document and a PE not supporting such
extension does not result in any problem.

(5.3.1 Ingress PE Support the Extension but Egress PE Not)

If Control Word is not used on the Ethernet PW, there will be no CW
L-bit. The egress PE will forward the frame as per current standard.
This is correct as only Root ACs exist on a PE not supporting the
extension specified in this document.  A Root AC can receive from any
other ACs.

By the way I recently posted a draft "Requirements for MEF E-Tree
Support in VPLS" 
(http://tools.ietf.org/html/draft-key-l2vpn-vpls-etree-reqt-00)
trying to start a "solution-neutral" discussion on whether there is a
valid requirement to enhance VPLS or not. Any comments on that draft?

Thanks,
Raymond 

> Delregno, Christopher N (Nick DelRegno) <[email-masked]>
wrote:
> 
> Raymond:
> 
> From a purely T-LDP perspective, I agree.  However, if we are relying 
> on CW to indicate leaf/root and the targeted PE doesn't support CW, 
> then the ETREE model breaks as I can no longer determine leaf/root and

> drop/forward traffic accordingly.  As such, the implementation 
> behavior when using CW to indicate Leaf/Root MUST NOT allow the CW 
> preference mismatch to result in an active PW.
> 
> Thanks,
> Nick
> 
> -----Original Message-----
> From: Raymond Key [mailto:[email-masked]]
> Sent: Wednesday, April 21, 2010 4:55 PM
> To: Delregno, Christopher N (Nick DelRegno)
> Cc: [email-masked]
> Subject: Re: Updated minutes from IETF 77
> 
> Hi Nic,
> 
> I go through the recently published IETF77 L2VPN minutes and would 
> like to follow up on one of your comments.
> 
> Extract from minutes under
> 10) Extension to VPLS for E-Tree
> "Nic: This requires a control word, so a box has to support a control 
> word.
> PW mustn't come up if a CW is not supported."
> 
> There may be some confusion here. When one PE does not support control

> word, PW can still come up.
> 
> Refer to Section 5.2. Control Word (under Backward Compatibility) For 
> backward compatibility reason, use of Control Word on Ethernet PW is 
> not mandatory. If the PE on the other end prefers not to use Control 
> Word or does not support Control Word (which implies such PE does not 
> support the extension specified in this document), then Control Word 
> will not be used on the Ethernet PW.
> Refer to Appendix A for different Control Word scenarios.
> (http://tools.ietf.org/html/draft-key-l2vpn-vpls-etree-02#section-5.2)
> 
> Regards,
> Raymond Key
> 
> 
> > Giles Heron <[email-masked]> wrote:
> > 
> > Ok - so it'd help if I actually put some content in my email.
> > 
> > As Simon Delord helpfully pointed out the other day I missed the 
> > second half of the meeting out when I posted these.
> > 
> > I've now updated the online minutes:
> > 
> > http://www.ietf.org/proceedings/10mar/minutes/l2vpn.txt
> > 
> > Giles

---

From: Raymond Key <[email-masked]>
Date: Wed, 05 May 2010 07:55:59 +1000

Hi Nick.
Comments in line.
Raymond

> Delregno, Christopher N (Nick DelRegno) <[email-masked]> wrote:
> 
> Ray:
> 

[RK] Agree and will revise text in next version.

> it is on my to-do list...

[RK] Thanks