[rbridge] Proposed resolution of DRB election/MTU testing

[Donald Eastlake]

The set of VLANs on which Hellos need to sent is specified in Section
4.2.4.2 "Hello VLAN Tagging", pages 34-36 of
http://tools.ietf.org/id/draft-ietf-trill-rbridge-protocol-12.txt

A sketch of a proof that that is a sufficient set of VLANs appears in
Section 4 "No Persistent Loops", starting page 11 of
http://tools.ietf.org/id/draft-eastlake-trill-rbridge-notes-01.txt

Thanks,
Donald

On Fri, May 1, 2009 at 12:21 PM, mike shand <mshand at cisco.com> wrote:
> James Carlson wrote:
>
> Ali Sajassi (sajassi) writes:
>
>
> Regarding your comment that loop can happen as the result of one-way
> connectivity via partitioned VLAN, AFAIK DRB selection is done over
> designated VLAN and if that VLAN is partitioned, then the bridged
> network is partitioned because this VLAN is expected to be reachable via
> all the access ports. And if the bridged network is partitioned, the it
> is O.K. to have a DRB for each of the partitions. So, where is the loop?
>
>
> Suppose A and B are RBridges that are communicating over VLAN 1 as the
> primary VLAN.  They're forwarding for VLANs 2, 3, and 4 as well.
>
> Now suppose that VLAN 1 becomes partitioned.  Both can now become DRB.
> They are still forwarding for those other VLANs, though, and this
> potentially means we have two forwarders on the same VLAN, which leads
> to fatal forwarding loops.
>
> It's a problem that's specific to TRILL, because of the L2 work that
> it does.  It's not something that would happen with an L3 protocol.
>
>
>
> So does this mean that all these hellos need to be sent on all the VLANs?
>
>     Mike
>
>
>
>
>
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 Donald E. Eastlake 3rd   +1-508-634-2066 (home)
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