Subject: Re: draft-ietf-pwe3-ethernet-encap-02.txt: Tagged mode

From: Eric Rosen <[email-masked]>
Date: Fri, 21 Mar 2003 14:59:58 -0500

I  don't think  we'll make  any progress  by turning  this into  a religious
issue. 

FWIW, here is my take on the issue. 

At  a given interface,  we can  distinguish between  the "service-delimiting
tags" (which we might also call "provider tags") and the "customer tags". 

The  customer tags  are  meaningless to  the  provider, and  must be  passed
transparently through  the PW.  A provider  tag, if present, is  used by the
provider to identify a particular customer. 

Whether a provider tag is used  at a particular interface is a local matter.
If a PW connects two interfaces, a provider tag may be used at zero, one, or
two of those interfaces.  If used at both of them, it may be the either same
or different  at the two  interfaces.  Therefore, I  think the best  rule is
"don't carry a provider tag on the pseudowire".  This is raw mode.

Note that raw mode requires that, if  a provider tag is used at a particular
interface, the forwarding hardware servicing  that interface must be able to
add and remove the tags.  Tagged mode seems useful if there is hardware that
cannot manipulate  the tags  in this manner,  but is otherwise  suitable for
providing  PWE3  functionality.   My   understanding  is  that  there  is  a
significant amount of deployed hardware which falls into this category.

The issue of whether tagged mode should  be part of the standard is just the
issue of  whether there  should be  a standard which  supports that  sort of
hardware,  and  which  tells you  how  to  interoperate  with that  sort  of
hardware.   I  don't think  anyone  has given  a  good  argument that  there
shouldn't be. 

Given that the purpose of  IETF standards is to facilitate interoperability,
my suggestion would be to leave  tagged mode in the document, though perhaps
as a "deprecated mode".

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From: Rahul Aggarwal <[email-masked]>
Date: Fri, 21 Mar 2003 12:24:07 -0800 (PST)

Hi Eric,

> significant amount of deployed hardware which falls into this category.

Very true.

> my suggestion would be to leave  tagged mode in the document, though perhaps

Just to clarify, what would 'deprecated' mean in this case..?

thanks,
rahul

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From: Ali Sajassi <[email-masked]>
Date: Mon, 24 Mar 2003 01:41:45 -0800

>my suggestion would be to leave  tagged mode in the document, though perhaps

I second that. Both raw and tagged modes have their own merits as discussed 
previously and we should support both of them at this point.

-Ali