Subject: [rbridge] TRILL behavior over 802.1AX interface (link aggregation)

From: gururam m <[email-masked]>
Date: Fri, 13 Jan 2012 15:24:10 +0530

Hi,
     Can anyone point me to TRILL RFC/draft that describes TRILL support
over multiple links/link aggregation (802.1AX) that provides details
related to

 1. Hello generation/reception
 2. Adjacency Formation
 3. DRB Election
 4. LSP generation

Regards
Ram
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---

From: Donald Eastlake <[email-masked]>
Date: Fri, 13 Jan 2012 09:59:45 -0500

Hi Ram,

On Fri, Jan 13, 2012 at 4:54 AM, gururam m <[email-masked]> wrote:
> over multiple links/link aggregation (802.1AX) that provides details related
> to
>

TRILL operates above the ports of an RBridge and RFC 6325 mentions
802.1AX as a function that is implemented inside RBridge ports. In
particular, Appendix C says link aggregation occurs "below TRILL". On
multi-destination traffic over parallel non-pseudo-node links visible
to TRILL, see Section 4.5.2, particularly item 3, of RFC 6325.

draft-ietf-trill-rbridge-bfd-01 says:

   If lower level mechanisms, such as link aggregation [802.1AX], are in
   use that present a single logical interface to TRILL IS-IS, only a
   single TRILL BFD session can be established to any other RBridge over
   this logical interface.  However, lower layer OAM could be aware of
   and/or run separately on each of the components of an aggregation.

Section 3.5 of RFC 6327 says:

   There can be multiple parallel adjacencies between neighbor RBridges
   that are visible to TRILL.  (Multiple low-level links that have been
   bonded together by technologies such as link aggregation [802.1AX]
   appear to TRILL as a single link over which only a single TRILL
   adjacency could be established.)

   Any such links that have pseudonodes (see Section 6) are
   distinguished in the topology; such adjacencies, if they are in the
   Report state, appear in LSPs as per Section 6.  However, there can be
   multiple parallel adjacencies without pseudonodes because they are
   point-to-point adjacencies or LAN adjacencies for which a pseudonode
   is not being created.  Such parallel, non-pseudonode adjacencies in
   the Report state appear in LSPs as a single adjacency.  ...

In general, TRILL as currently specified, operates at layer two and a
half, below Layer 3 routing but above bridging. The idea is that link
aggregation is invisible to TRILL. As far as TRILL is concerned, the
aggregation is just a single point-to-point link. Or, more precisely,
the termination of the link aggregation over more than one RBridge
port appears to TRILL to be a single port.

Note that you could have RB1==CB==RB2 where CB is a customer bridge
between two RBridges. Since RBridge ports are, for the most part,
customer bridge ports, you could, for example, have link aggregation
over, say, three physical links from RB1 to CB and just a single
physical link from CB to RB2. Or you could have a link aggregation
over 3 physical links between RB1 and CB and a link aggregation of
five physical links between CB and RB2. All this is invisible to TRILL
on RB1 and RB2 that each just see a single port.

If there are multiple parallel links visible to TRILL, then all the
Adjacency mechanisms in RFC 6327/6325 operate separately on them. The
only thing to keep in mind is that all the non-pseudo-node parallel
adjacencies visible to TRILL are reported in LSP as a single
adjacency.

> Ram

Hope the above helps,

Thanks,
Donald
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