Subject: Couple of questions about the generalized pwid fec

From: "Vach Kompella" <[email-masked]>
Date: Tue, 20 Apr 2004 14:05:19 -0700

Eric,

Sec 5.2.3, para three (after What happens when PE2 receives such a Label
Mapping) says: In VPLS, the TAI would be a VPN-id, identifying a
particular VPLS instance.

I thought the AGI defined the VPLS instance.

Also, in the definition of the GPWID FEC:

AGI - 1 byte
Length - 1 byte
Value - variable

I have been objecting to this structure, but I think the problem was
more terminology: I wanted type, length, value.  However, we now have
the confusion that the AGI is only one byte, and defines the type of
Attachment Group Identifier.  The Length field is fine.  The Value field
is the actual name (within the namespace identified by the type of
Attachment Group Identifier).

In a nutshell, I agree with the structure, I disagree with the naming of
the fields.  The AGI field should be called AGI Type.  The Length, I
wish it were 2 bytes so that we would never run into an issue where the
name is some machine readable/generated thing, maybe a group
certificate?

Vach Kompella
IP Division, Alcatel
[email-masked]
+1 650 237-5152

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From: Eric Rosen <[email-masked]>
Date: Wed, 21 Apr 2004 00:01:17 -0400

Vach> Sec 5.2.3, para three (after What happens when PE2 receives such a Label
Vach> Mapping) says: In VPLS, the TAI would be a VPN-id, identifying a
Vach> particular VPLS instance.

Vach> I thought the AGI defined the VPLS instance.

Strictly speaking,  the TAI  includes the AGI  and the  TAII, so if  the AGI
identifiers the VPLS  instance, so does the TAI.  However,  it would be less
misleading just  to say "the AGI  identifies the VPLS  instance", or perhaps
just to refer to draft-ietf-l2vpn-signaling. 

Vach> I wanted type, length, value. 

I thought that's what it is now ;-)

Vach> The AGI field should be called AGI Type. 

I have no problem with this, others may have opinions though. 

Vach> The Length, I wish it were 2  bytes so that we would never run into an
Vach> issue where the name is some machine readable/generated thing, maybe a
Vach> group certificate? 

Or a DNS name? ;-)

A possible  alternative is to reserve the  first bit of the  length field to
indicate that  the length field  is two bytes  long.  Or the AGI  type might
determine the length of the length field.

---

From: "Vach Kompella" <[email-masked]>
Date: Wed, 21 Apr 2004 14:28:43 -0700

See below.

-Vach 

> -----Original Message-----
> From: Eric Rosen [mailto:[email-masked]] 
> 
> 
> Vach> Sec 5.2.3, para three (after What happens when PE2 
> receives such a 
> Vach> Label
> Strictly speaking,  the TAI  includes the AGI  and the  TAII, 
> so if  the AGI identifiers the VPLS  instance, so does the 
> TAI.  However,  it would be less misleading just  to say "the 
> AGI  identifies the VPLS  instance", or perhaps just to refer 
> to draft-ietf-l2vpn-signaling. 

Yes, to both.  I'll add the ref to draft-l2vpn-signaling.

> 
> Vach> The Length, I wish it were 2  bytes so that we would never run 
> Vach> into an issue where the name is some machine readable/generated 
> Vach> thing, maybe a group certificate?
> 
> Or a DNS name? ;-)
> 
> A possible  alternative is to reserve the  first bit of the  
> length field to indicate that  the length field  is two bytes 
>  long.  Or the AGI  type might determine the length of the 
> length field. 
> 

I don't think we need to be that stingy on a single byte, at the expense
of some additional parsing code.  Neither resource is an issue (i.e.,
more cycles on parsing and more memory/bandwidth for an extra byte), but
it makes it simpler to understand if it's just an unsigned short because
life's too complicated already.  Besides, that hack is used way too many
times in SNA :-)

-Vach

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From: Luca Martini <[email-masked]>
Date: Tue, 27 Apr 2004 09:47:49 -0600

>Yes, to both.  I'll add the ref to draft-l2vpn-signaling.
I'll change the control draft to say this as well.

Luca