Subject: [rbridge] Port configurations

From: Narendra kishore <[email-masked]>
Date: Thu, 12 May 2011 12:12:52 +0530

Hi Donald,

I need information on ports configurations in RBRidges.

Is the RBridge having 2 level of port configuration, i mean first Layer2
port configuration (Access, Trunk) and TRILL port configuration ( Access,
Trunk and None).
If there are 2 level port configuration then, can you please help me out a
bit in understanding the difference in those port configurations.

Also let me know whether AF can be appointed on Access port or Trunk port
(Layer2/TRILL).

Also please explain me a bit in the below paragraph present in AF Draft,

The Appointed Forwarder mechanism is irrelevant to any link on which
end station service is not offered. This includes links configured as
point-to-point and any link with all RBridge ports on that link
configured as trunk ports. (In TRILL, configuration of a port as a
"trunk port" just means that no end station service will be provided.
It does not imply that all VLANs are enabled on that port.)

Thanks and regards,
Naren
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From: Donald Eastlake <[email-masked]>
Date: Thu, 12 May 2011 22:40:07 -0400

Hi Narendra,

> port configuration (Access, Trunk) and TRILL port configuration ( Access,

Yes, you can view an RBridge port as having two layers.
     The lower layer (the one closest to the link) is the same as an
802.1Q-2005 bridge port except for how it handles some low level
bridging control frames. So you can configure that level the same ways
that you can configure an 802.1Q-2005 port. Can you point to a part of
the 802.1Q-2005 specification which defines "trunk port" and "access
port"? I believe the term "trunk port" is sometimes used at Layer 2 to
indicate a port connected to a point-to-point link between bridges
where all VLANs are enabled. What do you think it means to configure a
Layer 2 802.1Q-2005 port as an access port or a trunk port?
     For an incoming frame, the 802.1Q-2005 port classifies the frame
into a VLAN and mapped prority and, as the frame passes up through the
EISS interface provides the VLAN ID and priority as well as the
frame...

Then there is the TRILL port layer above the 802.1Q-2005 layer. At the
TRILL level, you can configure a port as point-to-point, trunk, or
access. As it says in the TRILL base protocol standard, there is a
dominance relations between these. point-to-point > access > trunk  If
you configure the port as point-to-point, the other two bits are
ignored. If you do not configure it as point-to-point in TRILL but
configure it as an access node then the trunk node bit is ignored.
Only if you do not configure it as point-to-point and do not configure
it as access does TRILL pay any attention to whether you have
configured it as trunk.

If you configure an TRILL port as point-to-point, the point-to-point
IS-IS Hellos are used on it and the assumption is that no other
devices are on the link including no end stations. So there is no end
station service offered by the port.

If you configure an TRILL port as a access port and not as a
point-to-point port, you are saying you want, as far as practical, to
use that port only for end station service. So no TRILL Data frames
should be sent through it and no TRILL IS-IS frames except Hellos for
loop safety.

If you configure an TRILL port as a trunk port and not as an access
port or a point-to-point port, then you are saying that you only want
to use the port for TRILL Data and TRILL IS-IS frames. No native
frames are sent and any received are discarded.

> bit in understanding the difference in those port configurations.

They are more or less independent. Incoming frames go through the
802.1Q-2005 layer up to the EISS and then the TRILL layer. Outgoing
frames go through the TRILL layer and then the EISS to the 802.1Q-2005
layer...

> Also let me know whether AF can be appointed on Access port or Trunk port

I don't know what you think a Layer 2 access port or a Layer 2 trunk
port are. But appointed forwarder status has nothing to do with the
lower 802.1Q-2005 layer of an RBridge port.

Configuring the TRILL layer of an RBridge port as an Access Port just
means you want to use it primarily for native frames. Of course the
full Appointed Forwarder logic applies to such a port.

Configuring the TRIL layer of an RBridge port as a Trunk Port means
that you don't want to use it for any native frames. I don't see why
you would appoint such a port forwarder for one or more VLANs since
they are not going to act as an appointed forwarder anyway.

> It does not imply that all VLANs are enabled on that port.)

I not sure how to clarify it much. "end station service" is ingressing
or egressing native frames. That's what appointed forwarders are all
about. If there is no end station service on a link, then no native
frames will be ingressed or egressed, no matter what you think you are
doing about appointing forwarders. So what you do about appointed
forwarders is "irrelevant", that is, it doesn't make any difference.

Thanks,
Donald
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