[rbridge] Comments on draft-ietf-trill-prob-02

[Eastlake III Donald-LDE008]

Hi Joe,

I have some comments as an individual on the latest Problem and
Applicability Statement draft. I think all the significant ones relate
to the problem statement Section 2:

Multipathing: bridge learning requires consistent symmetric paths. This
prohibits multipathing which improves bandwidth. (This is mentioned but
I think it deserves more emphasis.)

Something which, for want of a better term, I will call "quadratic
address lookup stress": The spanning tree (or each of them in the case
of MSTP) has a centroid. One is tempted to say root but, technically,
the root bridge can be anywhere in the tree, even at a leaf node. By
centroid, I mean the "center-of-traffic", where you have the most flows.
For most real world cases, I think, the one or two centroid nodes need
to learn the most addresses and they also have the highest bandwidth of
data. Thus they need to implement both the fastest and largest address
lookup facility, that is their learned address lookup is under quadratic
stress.

Rapid failover: I believe that RSTP (which is also used for each of the
trees in MSTP) determines a backup root port on each bridge so that it
can rapidly fail over to it if the primary path fails. So I think 802.1
bridge have this, to some extent.

Even if the attachment of a node is cryptographically authenticated,
stale information from an earlier attachment by that node is not
promptly updated but has to time out.



Most of my other comments are more editorial in nature. I'll send them
and some suggested text to you directly.

Thanks,
Donald
====================================================
 Donald E. Eastlake 3rd      +1-508-786-7554 (work)
 Motorola Laboratories
 111 Locke Drive
 Marlborough, MA 01752 USA
 Donald.Eastlake at motorola.com