[rbridge] Consensus Check: Point to Point links

[Eric Gray]

Donald,

	Perhaps all of these things are true. 

	So what?

	The argument that a lot of people would like to do X could
be used to do a lot of things.  I'd like us to make maple walnut 
waffle-cones - possibly with caramel on top. 

	Ummm, does that sound good! 

	What does ANY of this have to do with TRILL?

--
Eric Gray
Principal Engineer
Ericsson  

> -----Original Message-----
> From: rbridge-bounces at postel.org 
> [mailto:rbridge-bounces at postel.org] On Behalf Of Eastlake III 
> Donald-LDE008
> Sent: Wednesday, October 03, 2007 2:25 PM
> To: Rbridge at postel.org
> Subject: Re: [rbridge] Consensus Check: Point to Point links
> 
> Hi Eric,
> 
> I believe the generally understood meaning of point-to-point is a link
> with exactly two devices on it, in this case RBridges.
> 
> It is true that one could always do this sort of thing outside the
> standards. But in Chicago the working group appeared to 
> believe this was
> sufficiently important to say in the standard and, while the consensus
> in the room was not that detailed, I got the general impression that
> people would be favorable to, in a later management document, having a
> MIB variable that would enable one to configure an interface as being
> known point-to-point, possibly point-to-point, or prohibited 
> from using
> this point-to-point outer address flexibility, or some such management
> configuration feature. There also seemed to have been at least some
> interest in an automated way of determining that an interface was
> point-to-point, perhaps based on the receive of 802.1AB frames all
> containing appropriate indications coupled with the receipt 
> of no native
> frames.
> 
> Point-to-point links are, in fact, very common in modern 
> 802.3 networks.
> 
> Donald
> 
> -----Original Message-----
> From: Eric Gray [mailto:eric.gray at ericsson.com] 
> Sent: Wednesday, October 03, 2007 11:11 AM
> To: Eastlake III Donald-LDE008; Rbridge at postel.org
> Subject: RE: [rbridge] Consensus Check: Point to Point links
> 
> Donald,
> 
> 	Given that it is not crystal clear what you mean by 
> "point to point link", I am not sure I agree with this, at
> least as you have worded it here.
> 
> 	If you mean that the link is a full-duplex Ethernet
> link and the two end-points have some definitive mechansim
> for determining that they are the only entities using the
> link between them, there may be issues with doing this.
> 
> 	For example, if the link is technically an Ethernet 
> link, then it is not unlikely that one or the other devices 
> may have multiple roles - i.e. - it may be both an RBridge 
> for some frames and either a regular bridge or end station
> (for example, a router) for others.  It's arguable that, in
> this case, the multi-role device is two (or more) separate
> entities - thus invalidating a "point to point" definition
> for this case (though only two distinct physical devices
> are connected via this link).
> 
> 	Without a clear agreement between involved entities,
> this sort of "short-cut" addressing is likely to result in
> higher-level (slow path) processing of many (if not all) 
> of the frames transiting the link for some implementations.
> Moreover, without an unambiguous determination of exactly
> when this would apply, it will not be unambiguously clear
> when a receiving implementation would have to switch to a
> "promiscuous listening" mode.
> 
> 	I believe omission of the outer VLAN tag suffers from
> the same ambiguity.  For instance, it is possible for two
> devices to have a "point to point" relationship within a 
> VLAN context that would nto be the case without the VLAN
> context.
> 
> 	Hence it appears we would have to be explicit in what
> we mean by "point to point" link and how we expect that the
> entities (RBridges) involved would be able to disambiguate
> this p2p status for any given link.
> 
> 	If we are saying that two devices - using some means 
> out of scope for our specification - are somehow aware of an 
> unambiguous point-to-point relationship between them and can
> therefore use any MAC DA on transmission, and ignore it on
> receipt, we could make the same argument for virtually any 
> encapsulation choice we might prefer.  But, it would be as
> valid to observe that we don't need to specify what is - in
> essence - an out-of-context (mis)behavior between consenting 
> implementations...
> 
> --
> Eric Gray
> Principal Engineer
> Ericsson  
> 
> > -----Original Message-----
> > From: rbridge-bounces at postel.org 
> > [mailto:rbridge-bounces at postel.org] On Behalf Of Eastlake III 
> > Donald-LDE008
> > Sent: Tuesday, October 02, 2007 11:27 PM
> > To: Rbridge at postel.org
> > Subject: [rbridge] Consensus Check: Point to Point links
> > 
> > This is a check via the mailing list to confirm or refute 
> an apparent
> > consensus from the minutes of the Chicago meeting for a change from
> > protocol draft -05:
> > 
> >    If it is known that a link is a point to point link between two
> >    RBridges, then the outer header, if it is an Ethernet header, can
> >    have any source and/or destination addresses, those 
> addresses will
> >    be ignored on receipt, and the outer VLAN tag can be omitted.
> > 
> > If no particular controversy arises over this in the next two 
> > weeks, we
> > will declare it to be the working group consensus.
> > 
> > Thanks,
> > Donald & Erik
> > 
> > _______________________________________________
> > rbridge mailing list
> > rbridge at postel.org
> > http://mailman.postel.org/mailman/listinfo/rbridge
> > 
> 
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