Subject: [rbridge] multiple ports on same link

From: "Jeff Pickering" <[email-masked]>
Date: Fri, 6 Nov 2009 04:40:19 -0800

RB1 might have

   one set of ports, say { p1, p2, p3 } on one link, and another set of

   ports { p4, p5 } on a second link, and yet other ports, say p6, p7,

   p8, that are each on distinct links.  Let us call a set of ports on

   the same link as a "port group".

Ports dont know which port group they are in a-priori since this is determined

by external connectivity. Port group membership can only be determined by

examination of received pdus.

But since the hello pdus sent out all ports are currently identical, (if all

ports have the same mac, which is most common), there is no way for a port to

determine which "port group" it is in.

If we add a portId, like in a bpdu, to the trill hello this problem could be solved.

The spec currently doesnt mention such an identifier. What is the thinking here?

Jeff

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From: Donald Eastlake <[email-masked]>
Date: Fri, 6 Nov 2009 11:05:07 -0500

See below

> examination of received pdus.

Yes.

> determine which "port group" it is in.

There are lots of ways in which the Hellos might differ in their headers or
TLV contents but I suppose that the initial zero configuration Hellos from a
broken RBridge that had all its ports using the same MAC might be the same.

IS-IS Hello adjacency formation is fundamentally depending on every port on
the link having a different MAC.

DRB (or DIS (Designated Intermediate System) for layer 3) election is
depending on every port having a different MAC for tie breaking.

There are probably other dependencies on unique MAC addresses.

Having multiple ports with the same MAC violates the recommendations of IEEE
802-2001 and seems like a bad idea. In fact, a note in Section 9.2.3 of IEEE
802-2001 asserts that such ambiguous port MAC address assignment "does not
automatically meet the requirements of IEEE Std 802.1D-1998 MAC bridging".

> The spec currently doesnt mention such an identifier. What is the thinking

There was a provision for a "port id" in the Hellos due to confusion on this
point, but that is not how IS-IS does it. That provision was removed (see
Appendix Z, Changes from -10 to -11, item 4, in the base protocol draft).

Jeff

Thanks,
Donald

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From: Donald Eastlake <[email-masked]>
Date: Sat, 21 Nov 2009 19:59:24 -0500

Actually, there are ways in practice to handle all the ports on each device
having the same MAC assuming that that MAC is different between different
devices. In particular, this causes no problem until you have more than one
port of the same device on the same link. Since you can normally detect the
multiple port on a link condition in several ways, such as detecting a
received TRILL-Hello with your System ID or a source MAC that you know is
yours, this can be implemented.

Thanks,
Donald
=============================
Donald E. Eastlake 3rd   +1-508-634-2066 (home)
155 Beaver Street
Milford, MA 01757 USA
[email-masked]

On Fri, Nov 6, 2009 at 11:05 AM, Donald Eastlake <[email-masked]> wrote:

> Having multiple ports with the same MAC violates the recommendations of
> IEEE 802-2001 and seems like a bad idea. In fact, a note in Section 9.2.3 of
> IEEE 802-2001 asserts that such ambiguous port MAC address assignment "does
> not automatically meet the requirements of IEEE Std 802.1D-1998 MAC
> bridging".
>
>
> There was a provision for a "port id" in the Hellos due to confusion on
> this point, but that is not how IS-IS does it. That provision was removed
> (see Appendix Z, Changes from -10 to -11, item 4, in the base protocol
> draft).
>
> Jeff
>>
>
> Thanks,
> Donald
>
>