Subject: [trill] Shephard Review of draft-ietf-trlll-resilient-trees-

From: Donald Eastlake <[email-masked]>
Date: Fri, 26 May 2017 23:19:03 -0400

Summary:
     This draft is in reasonably good shape. I believe that after
fixing the things pointed out below, particularly the reference
updates, publication as an RFC should be requested.

Comments:
     It seems to me that there is a problem that Sections 3.2.1.1 and
3.2.2 use different methods for avoiding links in the primary
distribution tree (basically different ways of increasing those link's
cost) when calculating the backup tree. Furthermore, RBridges do not
signal which technique they are using so they could be inconsistency
which could lead to routing loops. To fix this would require
significant additional complexity. I believe the best solution is to
drop Section 3.2.2, which provides an alternative to the main method
in Section 3.2.1.1, as unnecessary.

In Section 5.2.1, I am also just a little concerned over the
operational aspects of method 1 for determining failure. I think
method 1 requires configuration not just of the timer value Td but
also configuration of some way to recognize packets that are in the
reliable stream. Standardizing how configure recognition of such
packets is problematic because different fast path hardware has
different abilities. So, probably the document should say that this
configuration out of scope.

Perhaps for people not familiar with the TRILL RPF check, it would be
good to mention in Section 5.2.2 that the egress RBridge can use the
RFP check logic to select packets on a particular tree, even if they
all arrive over the same link, because it can determine the tree a
packet is on from the TRILL Header.

Should probably add a tiny bit to the Security Considerations. Perhaps
one sentence saying "The IS-IS PDUs used to transmit the information
specified in Section 6 can be secured with IS-IS security [RFC5310]."

Terminology:
     Under separate cover I have sent suggested wording for entries
for Child and Parent.
     I think an RFC reference or two should be added for the BFD entry.

References:
     [RFC2119] needs to be added to the Normative References.
Reference to RFC 4601 needs to be updated to RFC 7761. References to
draft-ietf-rtgwg-mrt-frr-architecture needs to be updated to RFC 7812
(RFC 7821 is already included as an Informative Reference in the
document).

Thanks,
Donald (document Shepherd)
===============================
 Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
 155 Beaver Street, Milford, MA 01757 USA
 [email-masked]