Subject: [rbridge] How many trees, and per what

From: Eric.Gray at marconi.com (Gray, Eric)
Date: Sun, 5 Nov 2006 13:04:39 -0500

Clearly one of the things we need to talk about this week is what exactly
do we mean by ingress rbridge tree. 

--> -----Original Message-----
--> From: rbridge-bounces at postel.org 
--> [mailto:rbridge-bounces at postel.org] On Behalf Of Sanjay 
--> Sane (sanjays)
--> Sent: Friday, October 27, 2006 8:41 PM
--> To: Russ White; Radia.Perlman at sun.com
--> Cc: rbridge at postel.org
--> Subject: Re: [rbridge] How many trees, and per what
--> 
--> 
--> Russ, Radia, et. al.
--> 
--> Having a per-ingress rbridge tree, and using it for 
--> multicast delivery
--> has many issues
--> -- no scope for multicast multi-pathing/load-balancing
--> -- for an IP multicast that is only going to links with registered
--> receivers, we now need to build a state with 
--> # of ingress rbridges * # of groups. This is heavy on computation &
--> memory. 
--> 
--> Using shared multicast trees for multicast delivery avoids 
--> both above,
--> and the forwarding state is # of shared trees * # of groups. 
--> 
--> Also, instead of adding F-tag "values" to the context of 
--> the Rbridge-id,
--> why not treat "F-tag" as the Forwarding topology 
--> identifier. (quote from
--> http://www.ietf.org/internet-drafts/draft-gai-perlman-trill-
--> encap-00.txt
--> --> "The Forwarding Tag (FTag) identifies the forwarding topology
--> assigned to a given frame"). 
--> 
--> In the tree usage case (unknowns/multicast/broadcast), it's the tree
--> identifier. If flood/unknown packets are best sent using 
--> ingress-rbridge
--> tree, use the F-tag of the tree rooted at that ingress rbridge. If
--> multicast packets are best sent using shared-multicast 
--> trees, use the
--> F-tag of the (load-balanced) shared tree. 
--> 
--> Again, which tree/topology the packet is to be put onto, is 
--> the decision
--> made at the source/ingress rbridge. But once the tree is 
--> chosen, and the
--> F-tag is put on the packet, other rbridges honor the F-tag 
--> and forward
--> accordingly.  
--> 
--> -Sanjay
--> 
--> 
--> -----Original Message-----
--> From: Russ White [mailto:riw at cisco.com] 
--> Sent: Friday, October 27, 2006 3:02 PM
--> To: Radia.Perlman at sun.com
--> Cc: Sanjay Sane (sanjays); rbridge at postel.org
--> Subject: Re: [rbridge] How many trees, and per what
--> 
--> -----BEGIN PGP SIGNED MESSAGE-----
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--> 
--> > So the question is whether we should multiply the number 
--> of trees by 
--> > the number of F-tag values. And if so, how many F-tag values are
--> really needed.
--> 
--> I seem to be lost in the F-tag discussion, someplace.... Time warp,
--> anyone? :-)
--> 
--> My original impression was one tree per device per vlan 
--> throughout the
--> entire cloud, with some consideration for multicast still 
--> be taken in. I
--> don't really understand why we'd want one pre f-tag, maybe someone
--> should explain what we'd hope to gain through this?
--> 
--> :-)
--> 
--> Russ
--> 
--> - --
--> riw at cisco.com CCIE <>< Grace Alone
--> 
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