Subject: [rbridge] SPF verses STP, straight across the board

From: Eric.Gray at marconi.com (Gray, Eric)
Date: Fri, 3 Nov 2006 13:31:37 -0500

Silvano,

	 Not sure you have looked at my post to the WG on the subject
of using SPF for all cases.

	I have been assuming that SPF is used for all cases, as not
doing so produces problems.  Interestingly enough - from off-line
discussions - some of the problems I assume will happen if you mix
SPF (for unicast) and STP (for everything else), are exactly the
same as the problems you appear to be trying to address.

	Assume for a minute that all forwarding is based on SPF.  Do
the problems you're concerned about go away?

--
Eric

--> -----Original Message-----
--> From: Silvano Gai [mailto:sgai at nuovasystems.com] 
--> Sent: Thursday, November 02, 2006 9:29 PM
--> To: Gray, Eric; rbridge at postel.org
--> Subject: RE: [rbridge] SPF verses STP, straight across the board
--> 
--> 
--> Suppose that we have 5 RBridges, R1 to R5 and that R2 and R4 are
--> requesting a tree.
--> 
--> All the RBridges have the same LSA database propagated by ISIS.
--> They use Djikstra for the unicast core instance, putting 
--> themselves as
--> the root.
--> 
--> Then they also run two other instances of Djikstra, one 
--> using R2 as root
--> and one using R4 as root. As a result they put some port in 
--> forwarding
--> state and some in blocking state. Basically they compute 2 spanning
--> trees, one rooted in R2 (let's call it T2) and one rooted 
--> in R4 (T4),
--> without using the spanning tree protocol.
--> 
--> Each ingress RBridge can send multicast, broadcast and 
--> flooded frames
--> either on T2 or T4. It indicates its decision on the FTAG, which is
--> honored by all the other RBridges.
--> 
--> In this way the customer can get Shortest Path and also 
--> load balancing,
--> depending where he/she roots the trees. For example, in Fat Tree
--> networks, if you root the trees in the core, you get both.
--> 
--> -- Silvano
--> 
--> > -----Original Message-----
--> > From: rbridge-bounces at postel.org 
--> [mailto:rbridge-bounces at postel.org]
--> On
--> > Behalf Of Gray, Eric
--> > Sent: Thursday, November 02, 2006 2:34 PM
--> > To: rbridge at postel.org
--> > Subject: [rbridge] SPF verses STP, straight across the board
--> > 
--> > 
--> > There appears to be a late-blooming source of confusion 
--> relative to
--> > multicast, broadcast and flooded frame forwarding among RBridges.
--> > 
--> > The question is - do the concerns about efficient link utilization
--> > via the use of SPF routing apply to multicast, broadcast 
--> and flooded
--> > traffic (as they do to unicast traffic), or do we simply use some
--> > variation of STP to determine "spanning trees" for the non-unicast
--> > case?
--> > 
--> > I've been under the impression that the intention is to use SPF
--> > routing, straight across the board.
--> > 
--> > --
--> > Eric
--> > _______________________________________________
--> > rbridge mailing list
--> > rbridge at postel.org
--> > http://mailman.postel.org/mailman/listinfo/rbridge
-->