Margaret Wasserman wrote:
At 12:56 PM +0200 3/23/04, Jari Arkko wrote:
I think it would be possible to detect loops if we wanted really hard to do that. That might just
lead to reinvention of the spanning tree protocol, though.
This is a danger, yes.
Why is this a danger?
I think there's only a danger if we end up doing more work than we need to, or work on something covered by other standards bodies.
IMO, the ND proxy mechanism effectively does bridging at layer 3. What makes you think it will be any easier here than at layer 2? If layer 3 bridging is something that we need, then why not run STP?
I think that using the spanning tree algorithm may be OK, if we can work out appropriate root brouter selection, metrics etc.
I'd suggest that extending the coverage of a bridged network with 802.1d/w spanning tree protocols is not a good idea though, for a number fo reasons.
Firstly, the computational/message complexity of STP is such that the convergence times will increase greatly by connecting disparate bridged networks. (Even just running a separate spanning tree amongst the proxies for a level of hierarchy would work better, as area 0 does in OSPF).
Secondly, there are several issues in 802.1d/w networks which are constraints due to the transparent nature of the bridging in these networks (no modification to L2 frames).
In a proxied network, we can get much more control of the forwarding plane by changing the L2 headers. This may allow us to avoid the lack of redundancy present in spanning trees (for example using DAGs or shortest paths instead for unicast forwarding).
So L3 spanning trees may be one way to create a routing topology for ND/MLD proxies, but it may not be the best way.
There was some discussion of this general concept (zero-configuration routing and/or layer 3 bridging) in the Zerouter BOF and on the zerouter mailing list... Does anyone know if that effort is still active?
I'm not sure where zerouter work is at the moment.
The bof chair (Aidan Williams) was working at motorola labs in Sydney which has closed down. I've had difficulty tracking him down (mail bounces).
Radia Perlman and Aidan were working on this before. in a (now expired) draft.
http://www.watersprings.org/pub/id/draft-perlman-zerouter-rbridge-00.txt
Greg
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