As is customary, I have done my AD review of=C2=A0draft-ie=
tf-trill-resilient-trees-08.

=

--94eb2c03222ad727c40560a3f68e--

First, I would like to thank the authors M=
ingui, Tissa, Janardhanan, Ayan, and Anoop

for their work on this=
document.=C2=A0=C2=A0

Unfortunately, I have sever=
al serious concerns about this document.

First, an=
d most importantly, there is not a clear and mandatory algorithm for comput=
ing the backup distribution trees that is given. Sec 3.2.1.1 provides a rec=
ommendation that is still not fully specified.

I do see the idea =
that the root of a backup distribution tree need not be the same as the roo=
t of the primary distribution tree - but I see no indication of what decide=
s which the root is.=C2=A0 Perhaps it is the root of the primary distributi=
on tree?=C2=A0 =C2=A0 What is computing the backup distribution trees?=C2=
=A0 My assumption is that each RBridge does.=C2=A0 Can=C2=A0 a backup distr=
ibution tree be associated with only one primary distribution tree?=C2=A0

Second, I don't believe that the suggested algo=
rithm of raising the link costs for links used in a primary distribution tr=
ee will work to find maximally disparate paths.=C2=A0 Consider the simpler =
case with Suurballe's algorithm=C2=A0 (https://en.wikipedia.org/wiki/Suurballe=
's_algorithm) that is just looking for 2 disparate paths.=C2=A0 =C2=
=A0In that example, the shortest path is A-B-D-F which gives no disjoint pa=
th between A and F - but different pairs of paths are possible.

<=
br>

Obviously MRT (RFC7811) solves this issue - and it is possibl=
e to have different roots for the RED and BLUE trees by simply creating a p=
roxy node that attaches to the potential roots.=C2=A0 There may be a bit of=
work to be done - but it is similar to other proxy nodes used in RFC7811 a=
nd RFC7812.

You may have different solutions -=
and that is fine - but failing to fully specify an algorithm and having wh=
at is specified not work is not ok.

Third, pulling=
back and clearly explaining the different pieces of this technology is bad=
ly needed.=C2=A0 For instance:

=C2=A0 =C2=A0 (a) The root for a m=
ulticast distribution tree computes a backup distribution tree and identifi=
es the root to use.

=C2=A0 =C2=A0 (b) A PLR determines the backup=
distribution tree (how?)

=C2=A0 =C2=A0 (c) Each RBridge computes=
its part of the backup distribution tree - by pinning specific links into =
the backup distribution tree as advertised as affinity links (??)

=C2=A0 =C2=A0 (d) Is traffic looked for on the backup distribution tree?=
=C2=A0 How does a merge point/receiver make that decision?

Some of these details are in the draft - but it is quite hard to p=
ull out clearly.

Are there any implementations of =
this draft?

Regards,

Alia

=