Last Call Review of draft-ietf-nsis-rmd-
I have reviewed this document as part of the security directorate's
ongoing effort to review all IETF documents being processed by the
IESG. These comments were written primarily for the benefit of the
security area directors. Document editors and WG chairs should treat
these comments just like any other last call comments.
This document describes an NSIS QoS Model for networks that use the
Resource Management in Diffserv (RMD) concept. It describes RMD-QOSM,
which are new payloads sent using the GISP signaling mechanism, where
the new payloads request or reserve resources. A number of data flows
are discussed, depending on whether nodes within a network boundary
participate in the protocol or not.
The Security Considerations section covers the following topics:
- Byzantine adversaries (i.e., participants taken over by an
adversary) are a general problem, but this section intends to discuss
additional threats as a result of the new protocol. There is an
extensive discussion of on-path and off-path adversaries, which seems
to intend to be addressing Byzantine adversaries.
- RMD-QOSM is claimed to be lightweight, with different routers
allowed certain operations dependant on the role a router plays in the
system. E.g., only Ingress/Egress nodes are allowed to initiate
certain signaling messages.
- RMD-QOSM "relies on the security support that is provided by the
bounded end-to-end session, which is running between the boundaries of
the RMD domain", but doesn't mandate that security support.
The existing text is helpful, but not sufficient. The following points
are suggestions to improve this section.
1. The statement at the beginning of Security Considerations discusses
adversaries taking over a router, but the new threats are not very
clear. Are the authors considering that security associations are
revealed, that reservation data routed to a particular router can be
changed or forged, or something else?
2. The trust model used by RMD-QOSM is hinted at in the discussion of
on-path and off-path adversaries, but a discussion of exactly what
devices are trusted and what they're trusted to do would be helpful.
For example, is every interior router in the network is trusted to
handle any particular RESERVE or RESERVE` message? If not, then how
are the paths setup so that only authorized routers will see a
particular message? On the other hand, if routing is used to route the
messages then it would seem that any router must be authorized to
handle messages happened to be routed to them -- but then it isn't
clear that there can be a difference between an "on-path" and "off-
3. Another dimension of trust model is the fact that ingress/egress
routers seem to trust each other more than they trust interior nodes.
This seems evidenced by the fact that RESERVE messages (Figure 24)
don't seem to be intended to be modified by the interior routers. In
the case of probes, I would expect that this would be especially
important, but probes do not seem to be specifically discussed in this
4. There don't seem to be any actual security requirements or
recommendations made on GIST messaging. As such, it isn't clear that
attackers that have not taken over a participant (i.e., a man in the
middle) are in any way foiled. I would expect to see more MUSTs and
SHOULDs in this section regarding message security. There are
statements in the I-D such as "In the situation a security association
exists" and "If we assume that the RESERVE/RESPONSE is sent with hop-
by-hop channel security". There should be some description of the
threats to the messaging by a non-participant, and stating what
available mechanisms MUST or SHOULD be used.
5. Since roles seem to be an important part of the security
considerations, it would be helpful to see discussion of the
different threats & requirements on the ingress/egress routers and the
internal routers in their different roles.
6. An important service of RMD-QOSM is admission control, but there
doesn't seem to be any discussion of how the ingress routers determine
whether or not reservation requests given to them are valid. I would
have thought that is of particular importance, but if it's considered
out of scope this section might mention that fact.
Hope that helps,