Internet DRAFT - draft-jadhav-roll-storing-rootack
draft-jadhav-roll-storing-rootack
ROLL R.A. Jadhav, Ed.
Internet-Draft 9 November 2021
Intended status: Standards Track
Expires: 13 May 2022
RPL Storing Root-ACK
draft-jadhav-roll-storing-rootack-03
Abstract
This document explains problems with DAO-ACK handling in RPL Storing
MOP and provides updates to RFC6550 to solve those problems.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 13 May 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Jadhav Expires 13 May 2022 [Page 1]
Internet-Draft Storing Root-ACK November 2021
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language and Terminology . . . . . . . . . . 3
2. Problems with DAO-ACK in Storing MOP . . . . . . . . . . . . 3
2.1. End to End Path Establishment Indication . . . . . . . . 4
2.2. Target node is unaware if it needs to retry the DAO . . . 5
2.3. RPL node acting as router for RULs . . . . . . . . . . . 6
3. Requirements for Root-ACK handling in Storing MOP . . . . . . 6
4. Root-ACK from Root . . . . . . . . . . . . . . . . . . . . . 6
4.1. Transit Information Option update in DAO message . . . . 6
4.2. Root sends Root-ACK addressed to Target . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
RPL [RFC6550] specifies a proactive distance-vector routing scheme
designed for LLNs (Low Power and Lossy Networks). RPL enables the
network to be formed as a DODAG and supports storing mode and non-
storing mode of operations. Non-storing mode allows reduced memory
resource usage on the nodes by allowing non-BR nodes to operate
without managing a routing table and involves use of source routing
by the Root to direct the traffic along a specific path. In storing
mode of operation the routing happens on hop-by-hop basis and
intermediate routers need to maintain routing tables.
DAO messaging helps to install downstream routing paths in the DODAG.
DAOs are generated on hop-by-hop basis. DAO may contain multiple RPL
Control Options. The Target Option identifies the address prefix for
which the route has to be installed and the corresponding Transit
Information Option identifies the parameters (such as lifetime,
freshness-counter, etc) for the target. The DAO base object contains
the 'K' flag indicating that a DAO-ACK is sought by the sender. The
DAO, DAO-ACK progresses on hop-by-hop basis all the way till Root.
In non-storing MOP, the DAO from the target node is directly
addressed to the Root and the Root responds with a DAO-ACK indicating
path establishment status. However, in storing MOP, the DAO-ACK is
immediately sent by the upstream parent. Thus in case of storing
MOP, the target node cannot rely on DAO-ACK as an indication that the
end to end (from the target node to Root) path has been established.
Jadhav Expires 13 May 2022 [Page 2]
Internet-Draft Storing Root-ACK November 2021
This draft highlights various issues with RPL DAO-ACK handling in
Storing MOP. Section 4 of [I-D.ietf-roll-rpl-observations] provides
more context to the problem statement. The draft provides
requirements to solve the issues and provides an updates to RFC6550
based on these requirements.
1.1. Requirements Language and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
MOP: Mode of Operation
NS-MOP: RPL Non-Storing Mode of Operation
S-MOP: RPL Storing Mode of Operation
Root-ACK: The Root-ACK syntax is same as DAO-ACK except that the
Root-ACK is addressed directly to the peer who owns the target
prefix. DAO-ACK in contrast is always sent using link-local IPv6
address in storing MOP.
DelayDAO: Section 9.5 of RFC6550 introduces a delay before the DAO
transmission is initiated.
TIO: (Transit Information Option) Section 6.7.8 of RFC6550. TIO is
an option usually carried in DAO message and augments control
information for the advertised Target.
RUL: (RPL Unaware Leaf) [I-D.ietf-roll-unaware-leaves]
This document uses terminology described in [RFC6550].
2. Problems with DAO-ACK in Storing MOP
Consider the following topology for the subsequent description:
Jadhav Expires 13 May 2022 [Page 3]
Internet-Draft Storing Root-ACK November 2021
(Root)
|
|
|
(A)
/ \
/ \
/ \
(B) -(C)
| / |
| / |
| / |
(D)- (E)
\ ;
\ ;
\ ;
(F)
/ \
/ \
/ \
(G) (H)
Figure 1: Sample topology
2.1. End to End Path Establishment Indication
Nodes need to know whether the end to end path till the Root has been
established before they can initiate application traffic. In case of
NS-MOP, the DAO is addressed to the Root from the Target node and the
Root sends DAO-ACK directly addressed back to the target node. Thus
in case of NS-MOP, the node can make use of this DAO-ACK as an
indication whether the necessary routes have been installed.
However, in case of Storing MOP, the DAO/DAO-ACK signaling happens at
every hop.
Non-Storing MOP
| D ======== B ======== A ======== (Root)
| ---------------DAO------------>
| <-----------DAO-ACK------------
|
V
time
Figure 2: NS-MOP DAO/DAO-ACK handling
Jadhav Expires 13 May 2022 [Page 4]
Internet-Draft Storing Root-ACK November 2021
Storing MOP
| D ======== B ======== A ======== (Root)
| ---DAO--->
| <-DAO-ACK-
| ---DAO--->
| <-DAO-ACK-
| ---DAO--->
| <-DAO-ACK-
V
time
Figure 3: Storing MOP DAO/DAO-ACK handling
Note that in Storing-MOP, the DAO/DAO-ACK signaling happens on hop-
by-hop basis and a DelayDAO timer is used before intermediate 6LRs
generate the DAO. This would mean that the DAO reaching the Root may
take several seconds. The target node should not generate the
application traffic unless the end to end path is established.
Consider Figure 1, when node D sends a DAO, the node B receives the
DAO and instantly sends back DAO-ACK. Node B then subsequently
generates the DAO with Target as Node D and sends it to node A. The
DAO with Target as Node D may take time (since the DAO is scheduled
with DelayDAO timer by every node) to finally reach the Root at which
point the end to end path is established. There is no way for node D
to know when the end to end path is established. This information is
needed for node D to initiate its application traffic. Initiating
application traffic prior to this might almost certainly lead to
application packet retries causing congestion in the network.
2.2. Target node is unaware if it needs to retry the DAO
It is possible that the intermediate 6LR goes down while attempting
to generate DAO on behalf of the target node. In this case, the
target node has no way of knowing to retry the DAO, in which case the
route installation may not happen until the target node's DAO
lifetime expires.
Consider Figure 1, assume that node A was generating DAO with Target
node D and sending it to Root. Node A reboots before attempting to
send DAO to Root. Node A has already sent DAO-ACK downstream to node
B. In this case, the target node D is not aware that sending DAO has
failed somewhere upstream. Note that as per RFC6550 upstream DAO is
scheduled based on DelayDAO but DAO-ACK is sent instantaneously on
DAO reception from downstream node.
Jadhav Expires 13 May 2022 [Page 5]
Internet-Draft Storing Root-ACK November 2021
2.3. RPL node acting as router for RULs
An RPL node may act as a router for RPL unware leaves as described in
[I-D.ietf-roll-unaware-leaves]. Ideally an RPL node should start
accepting RULs solicitation only after making sure that it has
established itself in the network first. In Storing-MOP, there is no
way to ascertain this.
3. Requirements for Root-ACK handling in Storing MOP
Following are the requirements:
Indicate end to end path establishment The Target node must know
when to initiate the application traffic based on end to end path
establishment.
Handle multiple targets in DAOs A DAO message may contain multiple
Target Options. The Root-ACK mechanism must handle multiple
targets in DAO.
Handle DAOs with address prefix RPL DAO Target Option may contain an
address prefix i.e., not the full address.
Provide suitable way for target node to retry The Target node must
have a way to know and retry the DAO in case the DAO transmission
fails enroute.
Backward compatible with current DAO-ACK The current per hop DAO-ACK
must function as it is. Legacy nodes should be able to operate
without any changes.
4. Root-ACK from Root
The draft defines a way for the RPL Root to send the Root-ACK back
directly addressed to the Target node. The Target node can receive
the Root-ACK directly thus getting an indication that the end to end
path till the Root has been successfully established. The Root-ACK
uses the same syntax and message code as DAO-ACK. The only
difference is that the Root-ACK is directly addressed to the Target
node who owns the advertised prefix in the Target Option.
4.1. Transit Information Option update in DAO message
The Target node indicates that it wishes to receive Root-ACK directly
from Root by setting the newly defined 'K' flag in Transit
Information Option.
Jadhav Expires 13 May 2022 [Page 6]
Internet-Draft Storing Root-ACK November 2021
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x06 | Option Length |E|I|K| Flags | Path Control |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Sequence | Path Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Updated Transit Information Option (New K flag added)
The K flag indicates that the Root of the RPLInstance MUST send a
Root-ACK directly to the target node.
4.2. Root sends Root-ACK addressed to Target
On receiving a DAO with Transit Information Option with 'K' flag set,
the Root MUST respond with a Root-ACK immediately to the address
extracted from the corresponding Target Option.
The Root-ACK MUST contain the Transit Information Option with
parameters copied from the DAO's Transit Information Option based on
which this Root-ACK was generated. The PathSequence in the Transit
Information Option helps the Target node to identify for which DAO it
generated it has received the Root-ACK. The DAOSequence in the base
Root-ACK(DAO-ACK) base object is ignored by the Target node.
5. IANA Considerations
IANA is requested to allocate bit 2 from the Transit Information
Option Flags registry for the 'K' flag (Section 4.1).
6. Security Considerations
This node introduces a new flag in response to which the Root of the
DODAG would send a Root-ACK which serves as an indication for the
target node that the end to end route/path is established. The Root-
ACK indication eventually would be used by the end node for
application layer processing such as initiating the application
traffic. A malicious node could generate the Root-ACK pre-maturely
i.e, before the end-to-end path is established and cause the
application to do some processing pre-maturely. However, the
application layer would always account for application layer failures
and thus shouldn't result in any security issues. This could result
in more control overhead which is currently the case where nodes do
not support this specification.
Jadhav Expires 13 May 2022 [Page 7]
Internet-Draft Storing Root-ACK November 2021
A malicious 6LR or 6LN could set the 'K' flag indicating the Root to
send a Root-ACK. The Root would generate a Root-ACK for the
indicated target. The Root need not keep any additional state for
handling the 'K' flag.
This document assumes that the security mechanisms as defined in
[RFC6550] are followed, which means that all the nodes are part of
the RPL network because they have the required credentials. A non-
secure RPL network needs to take into consideration the risks
highlighted in this section as well as those highlighted in
[RFC6550].
7. References
7.1. Normative References
[I-D.ietf-roll-unaware-leaves]
Thubert, P. and M. C. Richardson, "Routing for RPL
(Routing Protocol for Low-Power and Lossy Networks)
Leaves", Work in Progress, Internet-Draft, draft-ietf-
roll-unaware-leaves-30, 22 January 2021,
<https://www.ietf.org/archive/id/draft-ietf-roll-unaware-
leaves-30.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.
7.2. Informative References
[I-D.ietf-roll-rpl-observations]
Jadhav, R. A., Sahoo, R. N., and Y. Wu, "RPL
Observations", Work in Progress, Internet-Draft, draft-
ietf-roll-rpl-observations-06, 3 June 2021,
<https://www.ietf.org/archive/id/draft-ietf-roll-rpl-
observations-06.txt>.
Author's Address
Jadhav Expires 13 May 2022 [Page 8]
Internet-Draft Storing Root-ACK November 2021
Rahul Arvind Jadhav (editor)
Marathahalli
Bangalore 560037
Karnataka
India
Email: rahul.ietf@gmail.com
Jadhav Expires 13 May 2022 [Page 9]
