[rbridge] Consensus Check: Point to Point links

[Silvano Gai]

Joe,

If there is a bridge in between two RBridges you need to have a full
adjacency table.

If the link is point to point, you can save the table.

When the standard will be done, 40 and 100 Gb/s links will start to be
used.
On these links saving the adjacency table is a big deal.
It is not only the silicon cost, but also the memory bandwidth.

I don't see the additional complexity of a statement that says:
"on point-to-point link the MAC address xxxxxxxxx can be used as a
destination MAC".

-- Silvano

> -----Original Message-----
> From: Joe Touch [mailto:touch at ISI.EDU]
> Sent: Friday, October 05, 2007 12:05 AM
> To: Silvano Gai
> Cc: Eastlake III Donald-LDE008; Radia Perlman; Rbridge at postel.org
> Subject: Re: [rbridge] Consensus Check: Point to Point links
> 
> I do not understand the need to avoid a single entry per link. This is
> hyperoptimization at the expense of complexity, and isn't useful.
> 
> Joe
> 
> Silvano Gai wrote:
> > I agree with Donald on all points.
> > The saving comes from not having to maintain an adjacency table on
high
> > speed point-to-point links.
> >
> > -- Silvano
> >
> >> -----Original Message-----
> >> From: rbridge-bounces at postel.org
[mailto:rbridge-bounces at postel.org]
> > On
> >> Behalf Of Eastlake III Donald-LDE008
> >> Sent: Thursday, October 04, 2007 9:24 PM
> >> To: Radia Perlman
> >> Cc: Rbridge at postel.org
> >> Subject: Re: [rbridge] Consensus Check: Point to Point links
> >>
> >> Hi Radia,
> >>
> >> See below at @@@
> >>
> >> -----Original Message-----
> >> From: Radia Perlman [mailto:Radia.Perlman at sun.com]
> >> Sent: Thursday, October 04, 2007 11:51 AM
> >> To: Eastlake III Donald-LDE008
> >> Cc: Rbridge at postel.org
> >> Subject: Re: [rbridge] Consensus Check: Point to Point links
> >>
> >> Personally, I need a reminder of what we are trying to accomplish
with
> >> this before I can have
> >> any opinion.
> >>
> >> a) Is omitting the outer VLAN tag to save space?
> >>
> >> @@@ Yes. The outer VLAN tag does nothing for you on a
point-to-point
> >> link.
> >>
> >> b) Why put in anything for destination address other than the MAC
> >> address of the next hop
> >> RBridge, or put in anything into the source address other than your
> > own
> >> MAC address?
> >> It won't save space. So what does it gain?
> >>
> >> @@@ While no one has given a really crisp response to that
question,
> > it
> >> is my impression that some believe it will make it possible to
produce
> >> simpler, less expensive, or more efficient hardware for this case.
> >>
> >> c) Is there any danger if an RBridge is confused about whether this
is
> > a
> >> pt-to-pt link or not?
> >>
> >> @@@ I think there might be. And because of this and the extreme
> >> commonness of the point-to-point case, it may be reasonable to
> > consider
> >> this in designing TRILL. For example, if a fixed MAC address were
used
> >> (such as the unicast version of the All-Rbridges multicast address
> > (just
> >> turn off the group bit)), then an interface receiving a frame with
> > that
> >> source address would know there was a sender on the link who
believes
> >> the link was point-to-point. If the receiver knows it is not
> >> point-to-point or is unwilling to handle such frames, it could take
> >> appropriate action. Also, Rbridge would know to never bother
> > "learning"
> >> the location of that MAC address.
> >>
> >> @@@ Thanks,
> >> @@@ Donald
> >>
> >> I can see the advantage of omitting the entire outer header if it
is
> >> somehow absolutely
> >> known this is a pt-to-pt link, and both ends of the link understand
> >> this. But that isn't what's
> >> being proposed here. It seems to be only omitting the VLAN tag, and
> >> allowing insertion of
> >> random addresses into the source and destination fields in the
outer
> >> header, if I'm reading
> >> it correctly.
> >>
> >> So anyway, clarification at this point would certainly help me.
> >>
> >>
> >> Eastlake III Donald-LDE008 wrote:
> >>> 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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> >
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