Subject: [rbridge] Time to summarize "forward or block" BPDU thread

From: Radia.Perlman at sun.com ([email-masked])
Date: Mon, 17 Oct 2005 07:42:45 -0700

It works perfectly well if RBridges block. It isolates the bridge islands.

Routers also block bridge spanning tree, and to exactly the same
effect as if RBridges block BPDUs.

There is no interdependency if they block.

THere IS interdependency if RBridges forward BPDUs.

Radia
-------------- next part --------------

Saikat Ray wrote:
> AFAICT, this all works when there is at most one rbridge campus in an L2.
> 
> [Saikat] I think that the assumption (definition) is that if two RBridges
> are connected directly (i.e. no IP router in between), then they are parts
> of a single campus, thus must talk to each other. If that is true, then how
> would you have more than one campuses that are not separated by an IP
> router?

You won't - the rbridge campuses will merge.

But we're the IETF, and we're making 'rbridges', which will BLOCK.

Let's say the IEEE decides to allow another group to make 'sbridges',
which also decide to BLOCK.

Now you can have an rbridge and an sbridge in the same L2 (how do you
know you don't?). They form an undetectable, uncorrectable loop.

--

I.e. - this all works only if everyone plays by OUR rules. Since we're
NOT the IEEE, how is it that we can decide to create a protocol that
relies on us being the ONLY exception?

Joe
-------------- next part --------------
_______________________________________________
rbridge mailing list
rbridge at postel.org
http://www.postel.org/mailman/listinfo/rbridge

---

From: touch at ISI.EDU (Joe Touch)
Date: Mon, 17 Oct 2005 20:12:51 -0700

> effect as if RBridges block BPDUs.

This isn't the same at all; I keep hearing the analogy, but it fails
under all tests:

	first, there are NO routers on an L2 net

	all sources/sinks are the same (called nodes AFAICT)
	and hosts and routers are just nodes,
	identical as far as L2 is concerned

	nodes block all BPDUs (we agree), but
	nodes also block broadcast (rbridges don't)

Near as I can tell, L2 has exactly three devices currently:

	nodes

	links

	bridges (participate in SPT, interpret BPDUs)

Bridges don't 'block' BPDUs, but they don't forward them to all ports
either.

Now, an rbridge can be "like" a node, a link, or a bridge and still play
in the existing L2 specs. If it isn't 'like' any of those, then we're
changing the definition of 802, and I didn't think that was the goal here.

rbridges - at least to nodes on the L2 - are NOT 'like' hosts, since
they don't source or sink L2 traffic to existing nodes

rbridges could be 'like' links if they are TRANSPARENT

rbridges could be 'like' bridges if the PARTICIPATE

What exactly are rbridges 'like' if they BLOCK?

They can't be 'like' routers - there are no routers in L2.

??

Joe
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 254 bytes
Desc: OpenPGP digital signature
Url : http://www.postel.org/pipermail/rbridge/attachments/20051017/058e402c/signature.bin

---

From: Radia.Perlman at sun.com (Radia Perlman)
Date: Mon, 17 Oct 2005 22:58:59 -0700

I'm sorry, but I don't understand your example  (in a different
email), and don't understand why you think
isolating bridges into islands that create the illusion, to RBridges, of 
a single link can be a problem.
And I don't see why having RBridges as a layer above the bridges isn't 
the same as routers
being a layer above bridges.
And I can't think of a way of explaining it any differently. Perhaps 
somoene else can try,
or perhaps I can talk to you by phone sometime. But I'm travelling again.

Radia

Joe Touch wrote:

>------------------------------------------------------------------------
>

---

From: ssuryaputra at gmail.com (Stephen Suryaputra)
Date: Tue, 18 Oct 2005 08:08:46 -0400

Joe,

To me, Rbridge is changing the assumption that there is no router in
the L2 network. It fits well with the way L2 network view of routers,
they are nodes. From a directly connected L2 network, the Rbridge is
sourcing/sinking packets, and blocking (but accepting) broadcast. But
instead of terminating them (like nodes), Rbridge is tunneling them.

Another point why I think they are nodes, tunneling (i.e. the shim) is
using the unicast address of the ingress and egress Rbridges in the L2
header (no?).

Since the goal is to reduce the size of spanning tree protocol
network, the Rbridge chose not to tunnel BPDU. Tunneling is an option,
but that will make a cloud of Rbridges to be a virtual single bridge,
which IMHO can create more complex control for Rbridges. Tunnelling
BPDU however makes Rbridges look link links, very clean
architecturally.

So, now there are 4 devices in the L2 network: nodes, links, bridges
and Rbridges.

Cheers,

Stephen.

---

From: erik.nordmark at sun.com (Erik Nordmark)
Date: Wed, 19 Oct 2005 05:11:04 -0700

> What exactly are rbridges 'like' if they BLOCK?

I think they would be like IP multicast routers, but operating at L2 
instead of L3. Multicast routers, unlike IP unicast routers, need to be 
concerned with multiple next-hops picking up the same packet. Same issue 
appears for RBridges. The proposed solution for RBridges is what we have 
for multicast (a single elected forwarder).

    Erik