Subject: [PWE3] Comments on draft-vkompella-pwe3-ethernet-pw-bis-01

From: Shane Amante <[email-masked]>
Date: Wed, 30 Jul 2008 04:24:50 -0600

Per Stewart's request, this e-mail is restatement of the comments I made 
at the mic in yesterday's PWE3 WG meeting.

As I said as the mic, speaking as an individual contributor and network 
operator ...

First, if you look at the technology aspect of this proposal, then most 
people would probably agree that HW (and SW) are capable of operating an 
EoMPLS PW in just "raw" mode and putting the functions of pushing, 
popping, swapping VLAN tags and/or other Ethernet encapsulations "back" 
into the NSP.

IMO, we should be looking at this more from the point-of-view of a 
network operator.  Specifically, IMO, we (PWE3) are being much too 
rigorous in associating a given PW type with a particular (Ethernet) 
encapsulation in order to, for example, prevent a PW from coming up if 
encapsulations are mismatching on both sides to prevent blackholing of 
traffic.  However, there are also other legitimate reasons that we may 
not want to establish the PW as well, for example, due to mismatching 
MTU's on both sides (which, notably, ARE NOT bound to a PW type) ... 
ultimately, this is why we have a PW Control Protocol.

I do not think we (PWE3) should be forcing a choice made by us on all 
operators, particularly *within* the protocol (PW type) on when a PW 
will be established.  Specifically, there are a variety of reasons (see 
above) why one may not want to establish a PW.  So, we should be 
/consistent/ in how we're doing that.

Instead, we should be enabling the Control Protocol to exchange all 
kinds of "useful" information between two T-PE's to help operators 
debug/troubleshoot their network.  Outside of the base PW raw-mode (or 
GE-PW) protocol spec, we should specify a BCP as to an appropriate set 
of "default" behaviors/best-practices when it's not a good idea to 
establish a PW.  Vendors and operators can then point vendors at the BCP 
and say "you MUST to do this, by default" ... since, BCP's are still 
Standards Track.  On the other hand, other operators also have the 
flexibility to say: code your implementation to the BCP, *but* enable an 
"expert knob" in your box.  If one *consciously* configures their box 
with the "expert knob", then disable some or all of defaults in that 
BCP, because I just want to use the Control Protocol for debugging, but 
not use it to force a PW from never being established.

In conclusion, I think we're conflating the addition of a new PW type 
for a new Ethernet encapsulation with what the PW Control Protocol 
should really be doing.

-shane
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From: "BALUS Florin" <[email-masked]>
Date: Wed, 30 Jul 2008 20:16:23 -0500

Would like to add some comments to what Shane said below on the subject
of Ethernet PW types.

As you know a number of Ethernet tag types were defined up to now in
IEEE - e.g. IEEE 802.1q (VID), IEEE 802.1ad (QinQ SVID) and IEEE 802.1ah
(PBB I-tag). Others might be defined in the future. Each of them got
allocated a specific Ethertype. There were (and there will be) also a
number of proprietary code points assigned by vendors and deployed for
each of these tag types before IEEE had a chance to publish the standard
ones.

While these tags/combination of them may be present in the Ethernet
packet, there was no need up to now to assign different PW types for
each of them. The NSP implementations were able to look up the preceding
ethertype to identify which tag type is present and to process it
accordingly. 

(Note that the old Ethernet tagged PW was not added to differentiate
between different tags / Ethernet encapsulations. It was meant to insert
(at Tx side) and to  associate (at Rx side) a certain meaning to the tag
present after the PW header - i.e. "service delimiting tag" without
specifying which tag type to be used.) 

So I think we should not create in the future new PW types for each of
the new/old tag types.

Florin

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On Behalf
Of
> Shane Amante
> Sent: Wednesday, July 30, 2008 3:25 AM
> To: [email-masked]
> Subject: [PWE3] Comments on draft-vkompella-pwe3-ethernet-pw-bis-01
>