[rbridge] a clarification about the core IS-IS instance

[Anoop Ghanwani]

Donald,

Yes, I kind of got that after sending this note.
I guess it would be needed if someone intended
to use the per VLAN IS-IS instances.

Anoop 

> -----Original Message-----
> From: Eastlake III Donald-LDE008 
> [mailto:Donald.Eastlake at motorola.com] 
> Sent: Thursday, June 28, 2007 8:46 AM
> To: Anoop Ghanwani
> Cc: rbridge at postel.org
> Subject: RE: [rbridge] a clarification about the core IS-IS instance
> 
> If it were not for the V bit, how would you distinguish an 
> IS-IS routing
> packet conveying layer 3 routing information being sent inside a TRILL
> data frame from a layer 2 TRILL per VLAN IS-IS packet being 
> sent inside
> a TRILL IS-IS frame?
> 
> Donald
> 
> -----Original Message-----
> From: Anoop Ghanwani [mailto:anoop at brocade.com] 
> Sent: Thursday, June 28, 2007 10:34 AM
> To: Eastlake III Donald-LDE008
> Cc: rbridge at postel.org
> Subject: RE: [rbridge] a clarification about the core IS-IS instance
> 
> Hi Donald,
> 
> Thanks again.
> 
> What's the function of the V-bit in all
> of this?  What does an RBridge gain by looking
> at this, that it cannot get by looking at
> fields that it already has to?
> 
> Anoop 
> 
> > -----Original Message-----
> > From: Eastlake III Donald-LDE008 
> > [mailto:Donald.Eastlake at motorola.com] 
> > Sent: Thursday, June 28, 2007 7:30 AM
> > To: Anoop Ghanwani
> > Cc: rbridge at postel.org
> > Subject: RE: [rbridge] a clarification about the core IS-IS instance
> > 
> > Hi Anoop,
> > 
> > That looks about right, although you also have to check that 
> > the inner length/type field is in the length range. And if 
> > you determine that a TRILL IS-IS frame is for a per VLAN 
> > instance, you still don't know if you should process as well 
> > as forwarding it until you check whether you are DRB for a 
> > link with an end station in that VLAN.
> > 
> > Donald
> > 
> > -----Original Message-----
> > From: Anoop Ghanwani [mailto:anoop at brocade.com]
> > Sent: Thursday, June 28, 2007 10:00 AM
> > To: Eastlake III Donald-LDE008
> > Cc: rbridge at postel.org
> > Subject: RE: [rbridge] a clarification about the core IS-IS instance
> > 
> > Hi Donald,
> > 
> > Thanks for the clarification.  Yes, I do remember the 
> > discussion on the list.  At that time it looked like the 
> > Ethertype would tell if the frame was IS-IS.
> > It now looks like even the core IS-IS instance will use a 
> > DSAP/SSAP (for some reason I thought we were going to use a 
> > new Ethertype for the core IS-IS instance).
> > 
> > So, to identify a core IS-IS frame (which all RBridges should 
> > be interested in) one would have to check for:
> > outer.etype = trill
> > inner.dsap = xx
> > inner.ssap = xx
> > inner.ctl = yy
> > inner.vlan = not present
> > 
> > The V bit doesn't really seem all that useful since both the 
> > core frames and the per-VLAN instance have it set, so that 
> > bit doesn't tell one whether or the packet needs to be 
> > processed as a control packet at a given RBridge.  The above 
> > fields are necessary and sufficient.  Please let me know if 
> > I'm missing something re the V bit.
> > 
> > Thanks,
> > Anoop
> > 
> > > -----Original Message-----
> > > From: Eastlake III Donald-LDE008
> > > [mailto:Donald.Eastlake at motorola.com]
> > > Sent: Wednesday, June 27, 2007 9:09 PM
> > > To: Anoop Ghanwani
> > > Cc: rbridge at postel.org
> > > Subject: RE: [rbridge] a clarification about the core 
> IS-IS instance
> > > 
> > > Hi Anoop,
> > > 
> > > Yes, that was a change that was extensively discussed on 
> > the mailing 
> > > list. There wasn't a formal consensus determination but it 
> > was clear 
> > > that the sentiment of the group was to always have a TRILL 
> > Header on 
> > > TRILL IS-IS frames and use a formerly reserved bit in the 
> header to 
> > > distinguish a TRILL IS-IS frame from a TRILL data frame 
> > whose contents 
> > > happens to be a (presumably layer 3) IS-IS message.
> > > 
> > > I believe your second point is correct. Checking for the TRILL 
> > > Ethertype is the key to deciding whether to process a frame 
> > if you are 
> > > not DRB on that port and VLAN. (This ignores the 
> > bridging/media frames 
> > > sent to the block of multicast 16 addresses reserved for that 
> > > purpose.)
> > > 
> > > Thanks,
> > > Donald
> > > 
> > > -----Original Message-----
> > > From: rbridge-bounces at postel.org
> > > [mailto:rbridge-bounces at postel.org] On Behalf Of Anoop Ghanwani
> > > Sent: Wednesday, June 27, 2007 9:42 PM
> > > To: rbridge at postel.org
> > > Subject: [rbridge] a clarification about the core IS-IS instance
> > > 
> > > From reading the previous version of the draft I got the 
> impression 
> > > that frames sent as part of the core IS-IS would not 
> > contain a trill 
> > > header or inner header.  However, on reading this 
> version, it looks 
> > > like the core IS-IS instance would in fact contain a trill header.
> > > 
> > > Assuming that the above is true, would it be safe to 
> assume that an 
> > > RBridge, for a port that is connected to a LAN for which it 
> > is not a 
> > > DRB, will drop all frames whose Ethertype does not indicate trill?
> > > 
> > > Anoop
> > > 
> > 
>