[rbridge] Final outcome of outer VLAN tagsonRBridge-RBridgepackets?

Tue Oct 23 13:45:42 PDT 2007

Hi Silvano,

I have two questions:

(1) What exactly is the problem you see with doing adjacency on one
VLAN? It could be that you think that Hellos on one VLAN would be OK but
it is too much of a configuration burden to expect network
administrators to figure out which VLAN and to then configure their
Rbridges. Or it could be that you think that even if each port on each
Rbridge was configured to the "best" single VLAN, the adjacencies found
would be too sparse compared to those potentially possible. Or you could
think that both of these and/or other things are the main problem...

(2) If multiple Hellos on different VLANs, or some other technique, are
used to learn the full VLAN connectivity, what are Rbriges supposed to
do when no single VLAN will get to all the desired destinations? For
example, assume that Rbridge-A is connected as follows:

	On VLAN 2 to B and C
	On VLAN 3 to C, D, and E
	On VLAN 4 to F, G, and H
	On VLAN 5 to D, E, F, and G

If Rbrdige-A wants to send a multi-destination frame to all of B through
H, it would seem that it has to send it at least three times to get to
all the one-Rbridge-hop destinations and to avoid duplication. For
example, multicast on VLANs 3 and 4 and unicast to B. Or, alternatively,
multicast on VLANs 2 and 5 and unicast to H. Or, if the complexity
exceeds some threshold, Rbridge-A could just forget about optimality and
unicast the frame separately to B through H.

How would you suggest handling such situations?

Thanks,
Donald

-----Original Message-----
From: rbridge-bounces at postel.org [mailto:rbridge-bounces at postel.org] On
Behalf Of Silvano Gai
Sent: Tuesday, October 23, 2007 6:21 AM
To: Anoop Ghanwani; Radia Perlman; Developing a hybrid router/bridge.
Subject: Re: [rbridge] Final outcome of outer VLAN
tagsonRBridge-RBridgepackets?

I want to restate that IMHO a design that sends messages on a single
VLAN is so week to be completely useless.

I met Anoop on a plane back from a T11 meeting and we discussed the
issue of sending messages on all the configured VLANs. Anoop pointed out
that, if these messages are ISIS messages, this can overload the RBrige
supervisor.

We identified a possible solution based on two different message types:
- ISIS used on a single VLAN to compute adjacency
- simple per-VLAN checking on all the VLANs to verify reachability.

The second kind of messages is much simpler and therefore they load less
the RBrige supervisor. In the future, per-VLAN checking can be
implemented by the port ASIC. This seems a viable solution that requires
design effort, but it is promising.

Without the per-VLAN checking, running ISIS on a single VLAN holds water
like a pasta-strainer.

-- Silvano

> -----Original Message-----
> From: rbridge-bounces at postel.org [mailto:rbridge-bounces at postel.org]
On
> Behalf Of Anoop Ghanwani
> Sent: Monday, October 22, 2007 11:01 AM
> To: Radia Perlman; Developing a hybrid router/bridge.
> Subject: Re: [rbridge] Final outcome of outer VLAN tags onRBridge-
> RBridgepackets?
> 
> 
> If we want to make implementations work with
> only a single Hello for all VLANs than the
> option is (a).  I think that is what it should be.
> Basically, as a part of RBridge configuration
> there should be a "RBridge Control VLAN" configuration
> that applies to the whole device.  It should default
> to VLAN 1, but an operator can choose to change it.
> A RBridge only emits Hellos on that VLAN.  If it
> receives Hellos on any other VLAN that should
> be detected as an error condition and reported.
> 
> There have been some problem corner cases that
> have been pointed out previously on the list
> that may result in temporary duplication of
> traffic when there is misconfiguration.  Those
> should be documented.
> 
> Anoop
> 
> > -----Original Message-----
> > From: rbridge-bounces at postel.org
> > [mailto:rbridge-bounces at postel.org] On Behalf Of Radia Perlman
> > Sent: Saturday, October 20, 2007 9:47 PM
> > To: Developing a hybrid router/bridge.
> > Subject: [rbridge] Final outcome of outer VLAN tags on
> > RBridge-RBridgepackets?
> >
> > I'm not sure I understood the final consensus on what we
> > should do for outer VLAN tags on inter-RBridge packets.
> >
> > The possibilities I think the consensus might have been are:
> >
> > a) only use VLAN 1, explicit tag, no configuration possible.
> > b) default is VLAN 1, explicit tag, configuration is possible
> > to change sending with VLAN tag(s) something other than 1. If
> > this is what was decided, I don't believe we've worked out
> > the design details. I'd assume this would mean RBridges
> > should be willing to receive packets from other RBridges
> > regardless of outer VLAN tag. Would we then mark in the
> > Hellos what VLAN tag(s) you've heard from what other RBridges
> > with? What do we do with multicast if there isn't a single
> > VLAN tag that seems to work to send to everyone? Would we
> > allow configuration to send on a set of VLAN tags, or just on
> > one at a time (and we allow configuration to say which one it is)?
> >
> > Certainly a) is simpler. If the consensus was b), we'd better
> > work out the details.
> >
> > Radia
> > _______________________________________________
> > rbridge mailing list
> > rbridge at postel.org
> > http://mailman.postel.org/mailman/listinfo/rbridge
> >
> 
> _______________________________________________
> rbridge mailing list
> rbridge at postel.org
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