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

From: Raymond Key <[email-masked]>
Date: Sat, 24 Apr 2010 11:39:27 +1000

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: "UTTARO, JAMES (ATTLABS)" <[email-masked]>
Date: Mon, 26 Apr 2010 09:41:46 -0400

I guess  am still a bit confused as to how this would work when there
are leafs and roots on the same PE..

a) If Leafs are on the same PE how will the CW function? Will we need to
rely on some other mechanism to prevent Leaf<>Leaf traffic on the same
PE ?

b) Leaf->Root traffic on the same PE? We don't want the Root to simply
forward the traffic directly to another Leaf either on the PE or via a
PW to a remote PE.. How is this accomplished?

Comments In-Line..

Jim Uttaro

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of Raymond Key
Sent: Friday, April 23, 2010 9:39 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.

[Jim U>] From an SP perspective this approach represents a major
operational/provisioning challenge.. We would now need to track the set
of PEs that are candidates for Roots ( No CW Capable ), Roots and Leafs,
Leafs only. We cannot easily go back and change our homing rules. This
would also impact the provisonable footprint.

Thanks,
Raymond