[rbridge] Use of 802.1ah Encaps

[Gray, Eric]

Silvano,

	IFF we were going to use 802.1ah, it could allow us to  
use the "back-bone" DA/SA for next-hop/previous-hop and the
"customer" DA/SA for egress/ingress RBridges.  But that would 
be using it in a way that is not consistent with the intended
use of 802.1ah - simply because that usage would make use of 
the fields in a way that matches the way that your proposed 
"short-hand" SHIM header would use them.

	If you did that, there would be room for using the B-tag
and I-tag as analogues of your I-VLAN and O-VLAN tags.

	I think this is a VERY BAD idea.

--
Eric

> -----Original Message-----
> From: Silvano Gai [mailto:sgai at nuovasystems.com] 
> Sent: Friday, December 08, 2006 10:07 AM
> To: Ali Sajassi (sajassi); Don Fedyk; Gray, Eric
> Cc: Developing a hybrid router/bridge.; Joe Touch
> Subject: RE: [rbridge] Use of 802.1ah Encaps
> 
> Ali,
> 
> Inline:
> 
> > -----Original Message-----
> > From: Ali Sajassi (sajassi) [mailto:sajassi at cisco.com]
> > Sent: Thursday, December 07, 2006 9:23 PM
> > To: Silvano Gai; Don Fedyk; Gray, Eric
> > Cc: Developing a hybrid router/bridge.; Joe Touch
> > Subject: RE: [rbridge] Use of 802.1ah Encaps
> > 
> > 
> > Silvano,
> > 
> > > -----Original Message-----
> > > From: Silvano Gai [mailto:sgai at nuovasystems.com]
> > > Sent: Thursday, December 07, 2006 5:36 PM
> > > To: Don Fedyk; Gray, Eric; Ali Sajassi (sajassi)
> > > Cc: Developing a hybrid router/bridge.; Joe Touch
> > > Subject: RE: [rbridge] Use of 802.1ah Encaps
> > >
> > >
> > > IMO it is technically possible for TRILL to adopt IEEE 802.1ah.
> > > There are advantages and disadvantages.
> > >
> > > The disadvantages are:
> > > 1) Lack of Next-Hop addresses. We discussed this at length
> > > during the last meeting and we didn't reach consensus on a
> > > way to eliminate them.
> > 
> > Can you refresh my memory for why we need a next-hop 
> address when the
> > header carries both source and destination PE addresses and 
> when these
> > addresses are learned in control plane ?
> > 
> 
> Radia did in her reply
> 
> > > 2) Lack of a TTL field (it may be added, but it is not 
> there today).
> > 
> > Can probably be accommodated.
> > 
> > > 3) Many unneeded fields and therefore larger frame overhead.
> > >
> > 
> > Such as ?
> 
> The I-tag is not useful in TRILL and in contrast two addresses and the
> TTL are missing.
> 
> > 
> > > The advantages are:
> > > 1) Larger addressable market for TRILL
> > >
> > > IMO if we stick with the WG charter the disadvantages clearly
> > > outweigh the advantages.
> > >
> > > The WG can be re-chartered, but if we consider the Enterprise
> > > and Data Center market, IEEE 802.1ah is an overkill.
> > >
> > 
> > If by overkill you mean a bit bigger header, then I agree 
> but look at
> > all the other advantages that you get from using standard 
> IEEE header
> > and shim including:
> > 	- security Mgmt:  MACSec/KeySec
> > 	- Congestion Mgmt
> > 	- Connectivity Fault Mgmt
> > 
> > Has it been considered how these are going to work with TRILL shim
> > header or are these outside of WG charter :-)
> > 
> > -Ali
> > 
> > 
> > > -- Silvano
> > >
> > >
> > > > -----Original Message-----
> > > > From: rbridge-bounces at postel.org
> [mailto:rbridge-bounces at postel.org]
> > > On
> > > > Behalf Of Don Fedyk
> > > > Sent: Thursday, December 07, 2006 9:21 AM
> > > > To: Gray, Eric; Ali Sajassi (sajassi)
> > > > Cc: Developing a hybrid router/bridge.; Joe Touch
> > > > Subject: Re: [rbridge] Use of 802.1ah Encaps
> > > >
> > > > Hi Eric
> > > >
> > > > > -----Original Message-----
> > > > > From: Gray, Eric [mailto:Eric.Gray at marconi.com]
> > > > >
> > > > > Don,
> > > > >
> > > > > 	And yet, someone (Ali Sajassi) asserted (in his message
> > > dated Wed
> > > > > 12/6/2006 at 2:16 PM EST) that there were no issues or
> additional
> > > > > complications with using 802.1ah in enterprises for
> plug-and-play
> > > > > applicability.
> > > > >
> > > > > 	Perhaps Ali can answer my question then.
> > > > >
> > > > > 	But, to more directly address your earlier comments:
> > > > >
> > > > > 	The TRILL WG has NOT come up with an encapsulation that
> "looks
> > > > > like" 802.1ah - unless someone squints really hard 
> and tries to
> > > > > pretend that two separate Ethernet encapsulations -
> > > separated by a
> > > > > SHIM header - are one single encapsulation.
> > > >
> > > > To be fair Point to Point header that was discussed without
> > > one of the
> > > > shims was very close "functionally" (colloquial looks like) to
> > > 802.1ah.
> > > > My opinion is still we don't need several variations of
> > > headers doing
> > > > similar things.
> > > >
> > > > This was the slide that looked a lot like what I posted.
> > > >
> > > > http://www3.ietf.org/proceedings/06nov/slides/trill-1/sld13.htm
> > > >
> > > > Regards,
> > > > Don
> > > > >
> > > > > 	That is not to say that the WG has done anything that
> > > could be said
> > > > > to disallow the use of 802.1ah encapsulation.
> > > > > It is just not obviously consistent with all of the WG
> > > goals to use
> > > > > _only_ 802.1ah encapsulation.
> > > > >
> > > > > --
> > > > > Eric
> > > > >
> > > >
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> > >
>