Subject: [rbridge] Rbridge assumptions about bridged LANs

From: "Eastlake III Donald-LDE008" <[email-masked]>
Date: Wed, 4 Jun 2008 12:29:55 -0400

At the meeting in Philadelphia, it was requested that draft text which
might be included in the next version of the base protocol document
concerning assumptions about bridged LANs attached to Rbridges be posted
to the mailing list for comment. Some possible text is pasted at the end
of this message.

Thanks,
Donald
====================================================
 Donald E. Eastlake 3rd      +1-508-786-7554 (work)
 Motorola Laboratories
 111 Locke Drive
 Marlborough, MA 01752 USA
 [email-masked]

Rbridges make certain assumptions concerning the configuration
of the links connected to them, which may be bridged LANs.
Campuses will still be safe if these assumptions do not hold,
in that there will not be loops, unless the RBridges are
configured so as to disable their loop prevention features;
but some end stations may not be provided with connectivity
to the campus and some Rbridge ports may not be utilized.
If lack of connectivity occurs due to violation of these
assumptions, it can be restored by altering bridge
configurations so as to conform to the assumptions.

Rbridges assume that for every link with two or more Rbridges
on it, there will be at least one VLAN those RBridges are
configured to use that will provide bi-directional
connectivity between them. If this is not the case, one or
more of the Rbridges can become orphaned from the link and
not be usable for native traffic or transit TRILL data on
that link.

Rbridges attempt to provide connectivity between all
end stations in a particular VLAN but they assume this
is already the case within any bridged LAN to which they
are connected. If a bridge LAN is connected to a single
Rbridge, connectivity can only be provided to stations
in VLAN areas of that bridged LAN connect to the Rbridge
and where the Rbridge is appointed forwarder for that VLAN.
Should there be an island of some VLAN within the bridge
LAN with no access to the Rbridge, it will be isolated.
The same is true if the bridge LAN is connected to
multiple Rbridges. At most one such Rbridge will
be appointed forwarder for that VLAN and will provide
connectivity to end stations with a path to that Rbridge.
Should there be another island of stations in that VLAN
within the link, it will be isolated even if it has
connectivity to another Rbridge which is not the appointed
forwarder for the link and VLAN. 

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