[rbridge] Consensus Check: Point to Point links
eric.gray at ericsson.com
Wed Oct 3 12:10:04 PDT 2007
Perhaps all of these things are true.
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?
> -----Original Message-----
> From: rbridge-bounces at postel.org
> [mailto:rbridge-bounces at postel.org] On Behalf Of Eastlake III
> 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
> Point-to-point links are, in fact, very common in modern
> 802.3 networks.
> -----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
> 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
> 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
> Eric Gray
> Principal Engineer
> > -----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
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