Hi,
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.
The summary of the review is READY
nits:
ROLL Working Group M. Robles
Internet-Draft Aalto
Updates: 6553, 6550, 8138 (if approved) M. Richardson
Intended status: Standards Track SSW
Expires: September 12, 2019 P. Thubert
Cisco
March 11, 2019
Using RPL Option Type, Routing Header for Source Routes and IPv6-in-IPv6
encapsulation in the RPL Data Plane
draft-ietf-roll-useofrplinfo-25
Abstract
This document looks at different data flows through LLN (Low-Power
and Lossy Networks) where RPL (IPv6 Routing Protocol for Low-Power
and Lossy Networks) is used to establish routing. The document
enumerates the cases where RFC 6553 (RPL Option Type), RFC 6554
(Routing Header for Source Routes) and IPv6-in-IPv6 encapsulation is
required in data plane. This analysis provides the basis on which to
design efficient compression of these headers.
"""
s/on which//
s/. /. /
"""
This document updates
RFC 6553 adding a change to the RPL Option Type. Additionally, this
document updates RFC 6550 to indicate about this change and updates
RFC8138 as well to consider the new Option Type when RPL Option is
decompressed.
1. Introduction
RPL (IPv6 Routing Protocol for Low-Power and Lossy Networks)
[RFC6550] is a routing protocol for constrained networks. RFC 6553
[RFC6553] defines the "RPL option" (RPI), carried within the IPv6
Hop-by-Hop header to quickly identify inconsistencies (loops) in the
routing topology. RFC 6554 [RFC6554] defines the "RPL Source Route
Header" (RH3), an IPv6 Extension Header to deliver datagrams within a
There is certainly a reason for the RH3 spelling, but from 6554 it seems
to me that the abbreviation of Source Routing Header is SRH.
RPL routing domain, particularly in non-storing mode.
For my personal knowledge, I do not understand why this is specific to
non-storing mode. Is the reason that in non-storing modes nodes S steer
datagram D via the root node R. The IPv6 packet (S,D) is tunneled from S
to R and then from R to D. The first tunnel from S to R does not need
SRH as nodes are able to steer this to the root (upward routing), while
downward routing needs SRH extension.
In a storing mode *regular* routing tables are able to steer the traffic
from S, to D. There is no need of tunnel and SRH extension.
Am I correct, or I am missing something? I apology in advance for the
noise.
3. Updates to RFC6553, RFC6550 and RFC 8138
3.1. Updates to RFC 6553
This modification is required to be able to send, for example, IPv6
packets from a RPL-aware-leaf to a not-RPL-aware node through
Internet (see Section 6.2.1), without requiring IPv6-in-IPv6
encapsulation.
[RFC6553] states as shown below, that in the Option Type field of the
RPL Option header, the two high order bits must be set to '01' and
the third bit is equal to '1'. The first two bits indicate that the
IPv6 node must discard the packet if it doesn't recognize the option
type, and the third bit indicates that the Option Data may change in
route. The remaining bits serve as the option type.
Robles, et al. Expires September 12, 2019 [Page 5]
Internet-Draft RPL-data-plane March 2019
Hex Value Binary Value
act chg rest Description Reference
--------- --- --- ------- ----------------- ----------
0x63 01 1 00011 RPL Option [RFC6553]
Figure 1: Option Type in RPL Option.
Recent changes in [RFC8200] (section 4, page 8), states: "it is now
expected that nodes along a packet's delivery path only examine and
process the Hop-by-Hop Options header if explicitly configured to do
so". Processing of the Hop-by-Hop Options header (by IPv6
intermediate nodes) is now optional, but if they are configured to
process the header, and if such nodes encounter an option with the
first two bits set to 01, they will drop the packet (if they conform
to [RFC8200]). Host systems should do the same, irrespective of the
configuration.
Based on that, if an IPv6 (intermediate) node (RPL-not-capable)
receives a packet with an RPL Option, it should ignore the HBH RPL
option (skip over this option and continue processing the header).
This is relevant, as it was mentioned previously, in the case that
there is a flow from RPL-aware-leaf to Internet (see Section 6.2.1).
I might miss something, but it seems to me that 2460 would end up in the
discard of packets with the RPL Option. 8200 introduces some
instability. Typically, packets may reach their destination depending on
the configuration of the intermediary nodes. In both cases communication
between RPL-aware and not-RPL-aware nodes needs to relax the status of
the RPL Option. It seems independent to the update of 2460.
Thus, this document updates the Option Type field to: the two high
order bits MUST be set to '00' and the third bit is equal to '1'.
The first two bits indicate that the IPv6 node MUST skip over this
option and continue processing the header ([RFC8200] Section 4.2) if
it doesn't recognize the option type, and the third bit continues to
be set to indicate that the Option Data may change en route. The
remaining bits serve as the option type and remain as 0x3. This
ensures that a packet that leaves the RPL domain of an LLN (or that
leaves the LLN entirely) will not be discarded when it contains the
[RFC6553] RPL Hop-by-Hop option known as RPI.
This is a significant update to [RFC6553]. [RFCXXXX] represents this
document.
Hex Value Binary Value
act chg rest Description Reference
--------- --- --- ------- ----------------- ----------
0x23 00 1 00011 RPL Option [RFCXXXX]
Figure 2: Revised Option Type in RPL Option.
5. Use cases
NOTE: There is some possible security risk when the RPI information
is released to the Internet. At this point this is a theoretical
situation; no clear attack has been described. At worst, it is clear
that the RPI option would waste some network bandwidth when it
escapes. This is traded off against the savings in the LLN by not
having to encapsulate the packet in order to remove the artifact.
I believe that worst means minimal here. One of the risk is at least
marking the packet as originating to/from a LLN. It may reveal the type
of the information carried by the packet in addition to the information
contained in the RPI. Possible information leaked may be related to the
topology of the LLN, but I am not familiar enough to define clearly how
this could be exploited. The information may also reveals information
about the stability of the LLN by observing the rate. IF that is correct
this could eventually provide indication an attack is effective or not.
My understanding is that with 63 the packet is dropped after the first
non aware router, while this is not the case with 23.
Now that I have been through the security consideration section,
I believe a sinple reference to the security consideration woudl be
sufficient.
11. Security Considerations
The security considerations covered in [RFC6553] and [RFC6554] apply
when the packets are in the RPL Domain.
The IPv6-in-IPv6 mechanism described in this document is much more
limited than the general mechanism described in [RFC2473]. The
willingness of each node in the LLN to decapsulate packets and
forward them could be exploited by nodes to disguise the origin of an
attack.
While a typical LLN may be a very poor origin for attack traffic (as
the networks tend to be very slow, and the nodes often have very low
duty cycles) given enough nodes, they could still have a significant
impact, particularly if the attack was on another LLN!
maybe it might be clearer - at least to me, but I am not English native.
s/was on another LLN!/is targeting another LLN!/
Additionally,
some uses of RPL involve large backbone ISP scale equipment
[I-D.ietf-anima-autonomic-control-plane], which may be equipped with
multiple 100Gb/s interfaces.
Blocking or careful filtering of IPv6-in-IPv6 traffic entering the
LLN as described above will make sure that any attack that is mounted
must originate from compromised nodes within the LLN. The use of
BCP38 filtering at the RPL root on egress traffic will both alert the
operator to the existence of the attack, as well as drop the attack
traffic. As the RPL network is typically numbered from a single
prefix, which is itself assigned by RPL, BCP38 filtering involves a
single prefix comparison and should be trivial to automatically
configure.
There are some scenarios where IPv6-in-IPv6 traffic should be allowed
to pass through the RPL root, such as the IPv6-in-IPv6 mediated
communications between a new Pledge and the Join Registrar/
Coordinator (JRC) when using [I-D.ietf-anima-bootstrapping-keyinfra]
and [I-D.ietf-6tisch-dtsecurity-secure-join]. This is the case for
the RPL root to do careful filtering: it occurs only when the Join
Coordinator is not co-located inside the RPL root.
Robles, et al. Expires September 12, 2019 [Page 45]
Internet-Draft RPL-data-plane March 2019
With the above precautions, an attack using IPv6-in-IPv6 tunnels will
be by a node within the LLN on another node within the LLN. Such an
attack could, of course, be done directly. An attack of this kind is
meaningful only if the source addresses are either fake or if the
point is to amplify return traffic. Such an attack, could also be
done without the use of IPv6-in-IPv6 headers using forged source
addresses. If the attack requires bi-directional communication, then
IPv6-in-IPv6 provides no advantages.
[RFC2473] suggests that tunnel entry and exit points can be secured,
via the "Use IPsec". The suggested solution has all the problems
that [RFC5406] goes into. In an LLN such a solution would degenerate
into every node having a tunnel with every other node. It would
provide a small amount of origin address authentication at a very
high cost; doing BCP38 at every node (linking layer-3 addresses to
layer-2 addresses, and to already present layer-2 cryptographic
mechanisms) would be cheaper should RPL be run in an environment
where hostile nodes are likely to be a part of the LLN.
My understanding is that IPsec SA will be needed between each parent -
children and that a hop-by-hop decapsulation/encapsulation is happening.
If that is correct, we may avoid the situation where each node deals
with 2 * n *(n-1) SA. However without any transit devices IPsec provides
no obvious advantages over L2 security. It might be god to recommend
that one or the other layer implements security.
In addition, I am also wondering if the use of IPsec would not be
recommended as an alternative when LLN are involving communication over
the Internet.