[rbridge] query regd. TRILL scenario

[Donald Eastlake]

Hi Joybed,

On Mon, Jan 2, 2012 at 5:06 AM, Joydeb Roy <joydeb at gmail.com> wrote:
> Hi Authors,
>
> Please let me know if my understanding is proper in the below case. If yes,
> then please clarify the doubts and if no, then please correct wherever
> applicable.
>
> Generally, RBridges learn about end stations on access ports and they
> communicate with each other to form adjacency through trunk ports.  But if
> we consider the following diagram –

TRILL tries to be zero/minimum configuration. So by default, RBridge
ports are universal ports that can handle both native and TRILL Data
frames. RBridge access and trunk ports are ports that have been
configured to restrict them. While this is commonly a good idea, it is
not necessary for correct operation.

In any case, TRILL Hellos are always sent out RBridge ports unless the
port is disabled or configured as point-to-point (in which case
point-to-point Hellos get sent on them).

>                                   +---------+
> +---------+                       |   RB1   |
> |   End   |        +-----+ ------ +---------+
> |         | ------ | Hub |
> | Station |        +-----+ ------ +---------+
> +---------+                       |   RB2   |
>                                   +---------+
>
> How do the involved ports in RB1 and RB2 behave in this case? Do both of
> them manage to learn about the End Station and one of them becomes the DRB
> based upon the configured priorities? Also, do they manage to form an
> adjacency between them? If so, then how do they manage so in spite of the
> ports being designated as access?

As above, TRILL Hellos are still sent out the ports of RB1 & RB2
whether or not the "access port" configuration bit has been turned on
for those ports. So they form an adjacency and one is elected DRB on
the link. By default, the DRB will handle all the native traffic
to/from the End Station. The other RBridge will see all that traffic
but will throw it away because by default it is not the Appointed
Forwarder for any VLAN on the link. However, the DRB can assign some
or all VLANs to the non-DRB RBridge as Appointed Forwarder.

> Thank you.
>
> Best regards
> Joy

Hope the above helps.

Thanks,
Donald
=============================
 Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
 155 Beaver Street, Milford, MA 01757 USA
 d3e3e3 at gmail.com