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Versions: (draft-eckert-anima-stable-connectivity)
00 01 02 03 04 05 06 07 08 09 10 RFC 8368
ANIMA T. Eckert, Ed.
Internet-Draft Huawei
Intended status: Informational M. Behringer
Expires: January 28, 2018 July 27, 2017
Using Autonomic Control Plane for Stable Connectivity of Network OAM
draft-ietf-anima-stable-connectivity-04
Abstract
OAM (Operations, Administration and Maintenance - as per BCP161,
[RFC6291]) processes for data networks are often subject to the
problem of circular dependencies when relying on connectivity
provided by the network to be managed for the OAM purposes.
Provisioning during device/network bring up tends to be far less easy
to automate than service provisioning later on, changes in core
network functions impacting reachability may not be easy to be
automated either because of ongoing connectivity requirements for the
OAM, and widely used OAM protocols are not secure enough to be
carried across the network without security concerns.
This document describes how to integrate OAM with the autonomic
control plane (ACP) in Autonomic Networks (AN) to provide stable and
secure connectivity for conducting OAM. This connectivity is not
subject to aforementioned circular dependencies.
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 http://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 January 28, 2018.
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Copyright Notice
Copyright (c) 2017 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
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publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Self dependent OAM Connectivity . . . . . . . . . . . . . 2
1.2. Data Communication Networks (DCNs) . . . . . . . . . . . 3
1.3. Leveraging the ACP . . . . . . . . . . . . . . . . . . . 4
2. Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Stable Connectivity for Centralized OAM . . . . . . . . . 4
2.1.1. Simple Connectivity for Non-ACP capable NMS Hosts . . 5
2.1.2. Challenges and Limitation of Simple Connectivity . . 6
2.1.3. Simultaneous ACP and Data Plane Connectivity . . . . 7
2.1.4. IPv4-only NMS Hosts . . . . . . . . . . . . . . . . . 9
2.1.5. Path Selection Policies . . . . . . . . . . . . . . . 10
2.1.6. Autonomic NOC Device/Applications . . . . . . . . . . 12
2.1.7. Encryption of data-plane connections . . . . . . . . 12
2.1.8. Long Term Direction of the Solution . . . . . . . . . 13
2.2. Stable Connectivity for Distributed Network/OAM . . . . . 14
3. Security Considerations . . . . . . . . . . . . . . . . . . . 14
4. No IPv4 for ACP . . . . . . . . . . . . . . . . . . . . . . . 16
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
7. Change log [RFC Editor: Please remove] . . . . . . . . . . . 17
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
1.1. Self dependent OAM Connectivity
OAM (Operations, Administration and Maintenance - as per BCP161,
[RFC6291]) for data networks is often subject to the problem of
circular dependencies when relying on the connectivity service
provided by the network to be managed. OAM can easily but
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unintentionally break the connectivity required for its own
operations. Avoiding these problems can lead to complexity in OAM.
This document describes this problem and how to use the Autonomic
Control Plane (ACP) to solve it without further OAM complexity:
The ability to perform OAM on a network device requires first the
execution of OAM necessary to create network connectivity to that
device in all intervening devices. This typically leads to
sequential, 'expanding ring configuration' from a NOC (Network
Operations Center). It also leads to tight dependencies between
provisioning tools and security enrollment of devices. Any process
that wants to enroll multiple devices along a newly deployed network
topology needs to tightly interlock with the provisioning process
that creates connectivity before the enrollment can move on to the
next device.
When performing change operations on a network, it likewise is
necessary to understand at any step of that process that there is no
interruption of connectivity that could lead to removal of
connectivity to remote devices. This includes especially change
provisioning of routing, forwarding, security and addressing policies
in the network that often occur through mergers and acquisitions, the
introduction of IPv6 or other mayor re-hauls in the infrastructure
design. Examples include change of an IGP or areas, PA (Provider
Aggregatabe) to PI (Provider Independent) addressing, or systematic
topology changes (such as L2 to L3 changes).
All these circular dependencies make OAM complex and potentially
fragile. When automation is being used, for example through
provisioning systems, this complexity extends into that automation
software.
1.2. Data Communication Networks (DCNs)
In the late 1990'th and early 2000, IP networks became the method of
choice to build separate OAM networks for the communications
infrastructure within Network Providers. This concept was
standardized in ITU-T G.7712/Y.1703 [ITUT] and called "Data
Communications Networks" (DCN). These where (and still are)
physically separate IP(/MPLS) networks that provide access to OAM
interfaces of all equipment that had to be managed, from PSTN (Public
Switched Telephone Network) switches over optical equipment to
nowadays Ethernet and IP/MPLS production network equipment.
Such DCN provide stable connectivity not subject to aforementioned
problems because they are separate network entirely, so change
configuration of the production IP network is done via the DCN but
never affects the DCN configuration. Of course, this approach comes
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at a cost of buying and operating a separate network and this cost is
not feasible for many providers, most notably smaller providers, most
enterprises and typical IoT networks (Internet of Things).
1.3. Leveraging the ACP
One of the goals of the Autonomic Networks Autonomic Control Plane
(ACP as defined in [I-D.ietf-anima-autonomic-control-plane] ) is to
provide similar stable connectivity as a DCN, but without having to
build a separate DCN. It is clear that such 'in-band' approach can
never achieve fully the same level of separation, but the goal is to
get as close to it as possible.
This solution approach has several aspects. One aspect is designing
the implementation of the ACP in network devices to make it actually
perform without interruption by changes in what we will call in this
document the "data-plane", a.k.a: the operator or controller
configured services planes of the network equipment. This aspect is
not currently covered in this document.
Another aspect is how to leverage the stable IPv6 connectivity
provided by the ACP for OAM purposes. This is the current scope of
this document.
2. Solutions
2.1. Stable Connectivity for Centralized OAM
The ANI is the "Autonomic Networking Infrastructure" consisting of
secure zero touch Bootstrap (BRSKI -
[I-D.ietf-anima-bootstrapping-keyinfra]), GeneRic Autonomic Signaling
Protocol (GRASP - [I-D.ietf-anima-grasp]), and Autonomic Control
Plane (ACP - [I-D.ietf-anima-autonomic-control-plane]). Refer to
[I-D.ietf-anima-reference-model] for an overview of the ANI and how
its components interact and [RFC7575] for concepts and terminology of
ANI and autonomic networks.
This section describes stable connectivity for centralized OAM via
ACP/ANI starting by what we expect to be the most easy to deploy
short-term option. It then describes limitation and challenges of
that approach and their solutions/workarounds to finish with the
preferred target option of autonomic NOC devices in Section 2.1.6.
This order was chosen because it helps to explain how simple initial
use of ACP can be, how difficult workarounds can become (and
therefore what to avoid), and finally because one very promising
long-term solution alternative is exactly like the most easy short-
term solution only virtualized and automated.
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In the most common case, OAM will be performed by one or more
applications running on a variety of centralized NOC systems that
communicate with network devices. We describe differently advanced
approaches to leverage the ACP for stable connectivity. There is a
wide range of options, some of which are simple, some more complex.
Three stages can be considered:
o There are simple options described in sections Section 2.1.1
through Section 2.1.3 that we consider to be good starting points
to operationalize the use of the ACP for stable connectivity
today. These options require only network and OAN/NOC device
configuration.
o The are workarounds to connect the ACP to non-IPv6 capable NOC
devices through the use of IPv4/IPv6 NAT (Network Address
Translation) as described in section Section 2.1.4. These
workarounds are not recommended but if such non-IPv6 capable NOC
devices need to be used longer term, then this is the only option
to connect them to the ACP.
o Near to long term options can provide all the desired operational,
zero touch and security benefits of an autonomic network, but a
range of details for this still have to be worked out and
development work on NOC/OAM equipment is necessary. These options
are discussed in sections Section 2.1.5 through Section 2.1.8.
2.1.1. Simple Connectivity for Non-ACP capable NMS Hosts
In the most simple candidate deployment case, the ACP extends all the
way into the NOC via one or more "ACP edge devices" as defined in
section 6.1 of [I-D.ietf-anima-autonomic-control-plane]. These
devices "leak" the (otherwise encrypted) ACP natively to NMS hosts.
They acts as the default router to those NMS hosts and provide them
with IPv6 connectivity into the ACP. NMS hosts with this setup need
to support IPv6 (see e.g. [RFC6434]) but require no other
modifications to leverage the ACP.
Note that even though the ACP only uses IPv6, it can of course
support OAM for any type of network deployment as long as the network
devices support the ACP: The Data Plane can be IPv4 only, dual-stack
or IPv6 only. It is always spearate from the ACP, therefore there is
no dependency between the ACP and the IP version(s) used in the Data
Plane.
This setup is sufficient for troubleshooting such as SSH into network
devices, NMS that performs SNMP read operations for status checking,
software downloads into autonomic devices, provisioning of devices
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via NETCONF and so on. In conjunction with otherwise unmodified OAM
via separate NMS hosts it can provide a good subset of the stable
connectivity goals. The limitations of this approach are discussed
in the next section.
Because the ACP provides 'only' for IPv6 connectivity, and because
addressing provided by the ACP does not include any topological
addressing structure that operations in a NOC often relies on to
recognize where devices are on the network, it is likely highly
desirable to set up DNS (Domain Name System - see [RFC1034]) so that
the ACP IPv6 addresses of autonomic devices are known via domain
names that include the desired structure. For example, if DNS in the
network was set up with names for network devices as
devicename.noc.example.com, and the well known structure of the Data
Plane IPv4 addresses space was used by operators to infer the region
where a device is located in, then the ACP address of that device
could be set up as devicename_<region>.acp.noc.example.com, and
devicename.acp.noc.example.com could be a CNAME to
devicename_<region>.acp.noc.example.com. Note that many networks
already use names for network equipment where topological information
is included, even without an ACP.
2.1.2. Challenges and Limitation of Simple Connectivity
This simple connectivity of non-autonomic NMS hosts suffers from a
range of challenges (that is, operators may not be able to do it this
way) or limitations (that is, operator cannot achieve desired goals
with this setup). The following list summarizes these challenges and
limitations. The following sections describe additional mechanisms
to overcome them.
Note that these challenges and limitations exist because ACP is
primarily designed to support distributed ASA in the most lightweight
fashion, but not mandatorily require support for additional
mechanisms to best support centralized NOC operations. It is this
document that describes additional (short term) workarounds and (long
term) extensions.
1. (Limitation) NMS hosts cannot directly probe whether the desired
so called 'data-plane' network connectivity works because they do
not directly have access to it. This problem is similar to
probing connectivity for other services (such as VPN services)
that they do not have direct access to, so the NOC may already
employ appropriate mechanisms to deal with this issue (probing
proxies). See Section 2.1.3 for candidate solutions.
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2. (Challenge) NMS hosts need to support IPv6 which often is still
not possible in enterprise networks. See Section 2.1.4 for some
workarounds.
3. (Limitation) Performance of the ACP will be limited versus normal
'data-plane' connectivity. The setup of the ACP will often
support only non-hardware accelerated forwarding. Running a
large amount of traffic through the ACP, especially for tasks
where it is not necessary will reduce its performance/
effectiveness for those operations where it is necessary or
highly desirable. See Section 2.1.5 for candidate solutions.
4. (Limitation) Security of the ACP is reduced by exposing the ACP
natively (and unencrypted) into a LAN in the NOC where the NOC
devices are attached to it. See Section 2.1.7 for candidate
solutions.
These four problems can be tackled independently of each other by
solution improvements. Combining some of these solutions
improvements together can lead towards a candiate long term solution.
2.1.3. Simultaneous ACP and Data Plane Connectivity
Simultaneous connectivity to both ACP and data-plane can be achieved
in a variety of ways. If the data-plane is IPv4-only, then any
method for dual-stack attachment of the NOC device/application will
suffice: IPv6 connectivity from the NOC provides access via the ACP,
IPv4 will provide access via the data-plane. If as explained above
in the simple case, an autonomic device supports native attachment to
the ACP, and the existing NOC setup is IPv4 only, then it could be
sufficient to attach the ACP device(s) as the IPv6 default router to
the NOC LANs and keep the existing IPv4 default router setup
unchanged.
If the data-plane of the network is also supporting IPv6, then the
NOC devices that need access to the ACP should have a dual-homing
IPv6 setup. One option is to make the NOC devices multi-homed with
one logical or physical IPv6 interface connecting to the data-plane,
and another into the ACP. The LAN that provides access to the ACP
should then be given an IPv6 prefix that shares a common prefix with
the IPv6 ULA (see [RFC4193]) of the ACP so that the standard IPv6
interface selection rules on the NOC host would result in the desired
automatic selection of the right interface: towards the ACP facing
interface for connections to ACP addresses, and towards the data-
plane interface for anything else. If this cannot be achieved
automatically, then it needs to be done via IPv6 static routes in the
NOC host.
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Providing two virtual (e.g. dot1q subnet) connections into NOC hosts
may be seen as an undesired complexity. In that case the routing
policy to provide access to both ACP and data-plane via IPv6 needs to
happen in the NOC network itself: The NMS host gets a single
attachment interface but still with the same two IPv6 addresses as in
before - one for use towards the ACP, one towards the data-plane.
The first-hop router connecting to the NMS host would then have
separate interfaces: one towards the data-plane, one towards the ACP.
Routing of traffic from NMS hosts would then have to be based on the
source IPv6 address of the host: Traffic from the address designated
for ACP use would get routed towards the ACP, traffic from the
designated data-plane address towards the data-plane.
In the simple case, we get the following topology: Existing NMS hosts
connect via an existing NOClan and existing first hop Rtr1 to the
data-plane. Rtr1 is not made autonomic, but instead the edge router
of the Autonomic network ANrtr is attached via a separate interface
to Rtr1 and ANrtr provides access to the ACP via ACPaccessLan. Rtr1
is configured with the above described IPv6 source routing policies
and the NOC-app-devices are given the secondary IPv6 address for
connectivity into the ACP.
--... (data-plane)
NOC-app-device(s) -- NOClan -- Rtr1
--- ACPaccessLan -- ANrtr ... (ACP)
Figure 1
If Rtr1 was to be upgraded to also implement Autonomic Networking and
the ACP, the picture would change as follows:
---- ... (data-plane)
NOC-app-device(s) ---- NOClan --- ANrtr1
. . ---- ... (ACP)
\-/
(ACP to data-plane loopback)
Figure 2
In this case, ANrtr1 would have to implement some more advanced
routing such as cross-VRF routing because the data-plane and ACP are
most likely run via separate VRFs. A workaround without additional
software functionality could be a physical external loopback cable
into two ports of ANrtr1 to connect the data-plane and ACP VRF as
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shown in the picture. A (virtual) software loopback between the ACP
and data plane VRF would of course be the better solution.
2.1.4. IPv4-only NMS Hosts
ACP does not support IPv4: Single stack IPv6 management of the
network via ACP and (as needed) data plane. Independent of whether
the data plane is dual-stack, has IPv4 as a service or is single
stack IPv6. Dual plane management, IPv6 for ACP, IPv4 for the data
plane is likewise an architecturally simple option.
The downside of this architectural decision is the potential need for
short-term workarounds when the operational practices in a network
that cannot meet these target expectations. This section motivates
when and why these workarounds may be necessary and describes them.
All the workarounds described in this section are HIGHLY UNDESIRABLE.
The only recommended solution is to enable IPv6 on NMS hosts.
Most network equipment today supports IPv6 but it is by far not
ubiquitously supported in NOC backend solutions (HW/SW), especially
not in the product space for enterprises. Even when it is supported,
there are often additional limitations or issues using it in a dual
stack setup or the operator mandates for simplicity single stack for
all operations. For these reasons an IPv4 only management plane is
still required and common practice in many enterprises. Without the
desire to leverage the ACP, this required and common practice is not
a problem for those enterprises even when they run dual stack in the
network. We document these workarounds here because it is a short
term deployment challenge specific to the operations of the ACP.
To bridge an IPv4 only management plane with the ACP, IPv4 to IPv6
NAT can be used. This NAT setup could for example be done in Rt1r1
in above picture to also support IPv4 only NMS hots connected to
NOClan.
To support connections initiated from IPv4 only NMS hosts towards the
ACP of network devices, it is necessary to create a static mapping of
ACP IPv6 addresses into an unused IPv4 address space and dynamic or
static mapping of the IPv4 NOC application device address (prefix)
into IPv6 routed in the ACP. The main issue in this setup is the
mapping of all ACP IPv6 addresses to IPv4. Without further network
intelligence, this needs to be a 1:1 address mapping because the
prefix used for ACP IPv6 addresses is too long to be mapped directly
into IPv4 on a prefix basis.
One could implement in router software dynamic mappings by leveraging
DNS, but it seems highly undesirable to implement such complex
technologies for something that ultimately is a temporary problem
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(IPv4 only NMS hosts). With today's operational directions it is
likely more preferable to automate the setup of 1:1 NAT mappings in
that NAT router as part of the automation process of network device
enrollment into the ACP.
The ACP can also be used for connections initiated by the network
device into the NMS hosts. For example, syslog from autonomic
devices. In this case, static mappings of the NMS hosts IPv4
addresses are required. This can easily be done with a static prefix
mapping into IPv6.
Overall, the use of NAT is especially subject to the ROI (Return On
Investment) considerations, but the methods described here may not be
too different from the same problems encountered totally independent
of AN/ACP when some parts of the network are to introduce IPv6 but
NMS hosts are not (yet) upgradeable.
2.1.5. Path Selection Policies
As mentioned above, the ACP is not expected to have high performance
because its primary goal is connectivity and security, and for
existing network device platforms this often means that it is a lot
more effort to implement that additional connectivity with hardware
acceleration than without - especially because of the desire to
support full encryption across the ACP to achieve the desired
security.
Some of these issues may go away in the future with further adoption
of the ACP and network device designs that better tender to the needs
of a separate OAM plane, but it is wise to plan for even long-term
designs of the solution that does NOT depend on high-performance of
the ACP. This is opposite to the expectation that future NMS hosts
will have IPv6, so that any considerations for IPv4/NAT in this
solution are temporary.
To solve the expected performance limitations of the ACP, we do
expect to have the above describe dual-connectivity via both ACP and
data-plane between NOC application devices and AN devices with ACP.
The ACP connectivity is expected to always be there (as soon as a
device is enrolled), but the data-plane connectivity is only present
under normal operations but will not be present during e.g. early
stages of device bootstrap, failures, provisioning mistakes or during
network configuration changes.
The desired policy is therefore as follows: In the absence of further
security considerations (see below), traffic between NMS hosts and AN
devices should prefer data-plane connectivity and resort only to
using the ACP when necessary, unless it is an operation known to be
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so much tied to the cases where the ACP is necessary that it makes no
sense to try using the data plane. An example here is of course the
SSH connection from the NOC into a network device to troubleshoot
network connectivity. This could easily always rely on the ACP.
Likewise, if an NMS host is known to transmit large amounts of data,
and it uses the ACP, then its performance need to be controlled so
that it will not overload the ACP performance. Typical examples of
this are software downloads.
There is a wide range of methods to build up these policies. We
describe a few:
Ideally, a NOC system would learn and keep track of all addresses of
a device (ACP and the various data plane addresses). Every action of
the NOC system would indicate via a "path-policy" what type of
connection it needs (e.g. only data-plane, ACP-only, default to data-
plane, fallback to ACP,...). A connection policy manager would then
build connection to the target using the right address(es). Shorter
term, a common practice is to identify different paths to a device
via different names (e.g. loopback vs. interface addresses). This
approach can be expanded to ACP uses, whether it uses NOC system
local names or DNS. We describe example schemes using DNS:
DNS can be used to set up names for the same network devices but with
different addresses assigned: One name (name.noc.example.com) with
only the data-plane address(es) (IPv4 and/or IPv6) to be used for
probing connectivity or performing routine software downloads that
may stall/fail when there are connectivity issues. One name (name-
acp.noc.example.com) with only the ACP reachable address of the
device for troubleshooting and probing/discovery that is desired to
always only use the ACP. One name with data plane and ACP addresses
(name-both.noc.example.com).
Traffic policing and/or shaping of at the ACP edge in the NOC can be
used to throttle applications such as software download into the ACP.
MPTCP (Multipath TCP -see [RFC6824]) is a very attractive candidate
to automate the use of both data-plane and ACP and minimize or fully
avoid the need for the above mentioned logical names to pre-set the
desired connectivity (data-plane-only, ACP only, both). For example,
a set-up for non MPTCP aware applications would be as follows:
DNS naming is set up to provide the ACP IPv6 address of network
devices. Unbeknownst to the application, MPTCP is used. MPTCP
mutually discovers between the NOC and network device the data-plane
address and caries all traffic across it when that MPTCP subflow
across the data-plane can be built.
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In the Autonomic network devices where data-plane and ACP are in
separate VRFs, it is clear that this type of MPTCP subflow creation
across different VRFs is new/added functionality. Likewise, the
policies of preferring a particular address (NOC-device) or VRF (AN
device) for the traffic is potentially also a policy not provided as
a standard.
2.1.6. Autonomic NOC Device/Applications
Setting up connectivity between the NOC and autonomic devices when
the NOC device itself is non-autonomic is as mentioned in the
beginning a security issue. It also results as shown in the previous
paragraphs in a range of connectivity considerations, some of which
may be quite undesirable or complex to operationalize.
Making NMS hosts autonomic and having them participate in the ACP is
therefore not only a highly desirable solution to the security
issues, but can also provide a likely easier operationalization of
the ACP because it minimizes NOC-special edge considerations - the
ACP is simply built all the way automatically, even inside the NOC
and only authorized and authenticate NOC devices/applications will
have access to it.
Supporting the ACP all the way into an application device requires
implementing the following aspects in it: AN bootstrap/enrollment
mechanisms, the secure channel for the ACP and at least the host side
of IPv6 routing setup for the ACP. Minimally this could all be
implemented as an application and be made available to the host OS
via e.g. a tap driver to make the ACP show up as another IPv6 enabled
interface.
Having said this: If the structure of NMS hosts is transformed
through virtualization anyhow, then it may be considered equally
secure and appropriate to construct (physical) NMS host system by
combining a virtual AN/ACP enabled router with non-AN/ACP enabled
NOC-application VMs via a hypervisor, leveraging the configuration
options described in the previous sections but just virtualizing
them.
2.1.7. Encryption of data-plane connections
When combining ACP and data-plane connectivity for availability and
performance reasons, this too has an impact on security: When using
the ACP, the traffic will be mostly encryption protected, especially
when considering the above described use of AN application devices.
If instead the data-plane is used, then this is not the case anymore
unless it is done by the application.
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The simplest solution for this problem exists when using AN capable
NMS hosts, because in that case the communicating AN capable NMS host
and the AN network device have certificates through the AN enrollment
process that they can mutually trust (same AN domain). In result,
data-plane connectivity that does support this can simply leverage
TLS/DTLS ([RFC5246]/[RFC6347]) with mutual AN-domain certificate
authentication - and does not incur new key management.
If this automatic security benefit is seen as most important, but a
"full" ACP stack into the NMS host is unfeasible, then it would still
be possible to design a stripped down version of AN functionality for
such NOC hosts that only provides enrollment of the NOC host into the
AN domain to the extent that the host receives an AN domain
certificate, but without directly participating in the ACP
afterwards. Instead, the host would just leverage TLS/DTLS using its
AN certificate via the data-plane with AN network devices as well as
indirectly via the ACP with the above mentioned in-NOC network edge
connectivity into the ACP.
When using the ACP itself, TLS/DTLS for the transport layer between
NMS hosts and network device is somewhat of a double price to pay
(ACP also encrypts) and could potentially be optimized away, but
given the assumed lower performance of the ACP, it seems that this is
an unnecessary optimization.
2.1.8. Long Term Direction of the Solution
If we consider what potentially could be the most lightweight and
autonomic long term solution based on the technologies described
above, we see the following direction:
1. NMS hosts should at least support IPv6. IPv4/IPv6 NAT in the
network to enable use of ACP is long term undesirable. Having
IPv4 only applications automatically leverage IPv6 connectivity
via host-stack translation may be an option but the operational
viability of this approach is not well enough understood.
2. Build the ACP as a lightweight application for NMS hosts so ACP
extends all the way into the actual NMS hosts.
3. Leverage and as necessary enhance MPTCP with automatic dual-
connectivity: If an MPTCP unaware application is using ACP
connectivity, the policies used should add subflow(s) via the
data-plane and prefer them.
4. Consider how to best map NMS host desires to underlying transport
mechanisms: With the above mentioned 3 points, not all options
are covered. Depending on the OAM, one may still want only ACP,
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only data-plane, or automatically prefer one over the other and/
or use the ACP with low performance or high-performance (for
emergency OAM such as countering DDoS). It is as of today not
clear what the simplest set of tools is to enable explicitly the
choice of desired behavior of each OAM. The use of the above
mentioned DNS and MPTCP mechanisms is a start, but this will
require additional thoughts. This is likely a specific case of
the more generic scope of TAPS.
2.2. Stable Connectivity for Distributed Network/OAM
The ANI (ACP, Bootstrap, GRASP) can provide via the GRASP protocol
common direct-neighbor discovery and capability negotiation (GRASP
via ACP and/or data-plane) and stable and secure connectivity for
functions running distributed in network devices (GRASP via ACP). It
can therefore eliminate the need to re-implement similar functions in
each distributed function in the network. Today, every distributed
protocol does this with functional elements usually called "Hello"
mechanisms and with often protocol specific security mechanisms.
KARP (Keying and Authentication for Routing Protocols, see [RFC6518])
has tried to start provide common directions and therefore reduce the
re-invention of at least some of the security aspects, but it only
covers routing-protocols and it is unclear how well it applicable to
a potentially wider range of network distributed agents such as those
performing distributed OAM. The ACP can help in these cases.
3. Security Considerations
In this section, we discuss only security considerations not covered
in the appropriate sub-sections of the solutions described.
Even though ACPs are meant to be isolated, explicit operator
misconfiguration to connect to insecure OAM equipment and/or bugs in
ACP devices may cause leakage into places where it is not expected.
Mergers/Acquisitions and other complex network reconfigurations
affecting the NOC are typical examples.
ULA addressing as proposed in this document is preferred over
globally reachable addresses because it is not routed in the global
Internet and will therefore be subject to more filtering even in
places where specific ULA addresses are being used.
Random ULA addressing provides more than sufficient protection
against address collision even though there is no central assignment
authority. This is helped by the expectation, that ACPs are never
expected to connect all together, but only few ACPs may ever need to
connect together, e.g. when mergers and aquisitions occur.
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If packets with unexpected ULA addresses are seen and one expects
them to be from another networks ACP from which they leaked, then
some form of ULA prefix registration (not allocation) can be
beneficial. Some voluntary registries exist, for example
https://www.sixxs.net/tools/grh/ula/, although none of them is
preferable because of being operated by some recognized authority.
If an operator would want to make its ULA prefix known, it might need
to register it with multiple existing registries.
ULA Centrally assigned ULA addresses (ULA-C) was an attempt to
introduce centralized registration of randomly assigned addresses and
potentially even carve out a different ULA prefix for such addresses.
This proposal is currently not proceeding, and it is questionable
whether the stable connectivity use case provides sufficient
motivation to revive this effort.
Using current registration options implies that there will not be
reverse DNS mapping for ACP addresses. For that one will have to
rely on looking up the unknown/unexpected network prefix in the
registry to determine the owner of these addresses.
Reverse DNS resolution may be beneficial for specific already
deployed insecure legacy protocols on NOC OAM systems that intend to
communicate via the ACP (e.g. TFTP) and leverages reverse-DNS for
authentication. Given how the ACP provides path security except
potentially for the last-hop in the NOC, the ACP does make it easier
to extend the lifespan of such protocols in a secure fashion as far
to just the transport is concerned. The ACP does not make reverse
DNS lookup a secure authentication method though. Any current and
future protocols must rely on secure end-to-end communications (TLS/
DTLS) and identification and authentication via the certificates
assigned to both ends. This is enabled by the certificate mechanisms
of the ACP.
If DNS and especially reverse DNS are set up, then it should be set
up in an automated fashion, linked to the autonomic registrar backend
so that the DNS and reverse DNS records are actually derived from the
subject name elements of the ACP device certificates in the same way
as the autonomic devices themselves will derive their ULA addresses
from their certificates to ensure correct and consistent DNS entries.
If an operator feels that reverse DNS records are beneficial to its
own operations but that they should not be made available publically
for "security" by concealment reasons, then the case of ACP DNS
entries is probably one of the least problematic use cases for split-
DNS: The ACP DNS names are only needed for the NMS hosts intending to
use the ACP - but not network wide across the enterprise.
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4. No IPv4 for ACP
The ACP is targeted to be IPv6 only, and the prior explanations in
this document show that this can lead to some complexity when having
to connect IPv4 only NOC solutions, and that it will be impossible to
leverage the ACP when the OAM agents on an ACP network device do not
support IPv6. Therefore, the question was raised whether the ACP
should optionally also support IPv4.
The decision not to include IPv4 for ACP as something that is
considered in the use cases in this document is because of the
following reasons:
In SP networks that have started to support IPv6, often the next
planned step is to consider moving out IPv4 from a native transport
as just a service on the edge. There is no benefit/need for multiple
parallel transport families within the network, and standardizing on
one reduces OPEX and improves reliability. This evolution in the
data plane makes it highly unlikely that investing development cycles
into IPv4 support for ACP will have a longer term benefit or enough
critical short-term use-cases. Support for IPv4-only for ACP is
purely a strategic choice to focus on the known important long term
goals.
In other type of networks as well, we think that efforts to support
autonomic networking is better spent in ensuring that one address
family will be support so all use cases will long-term work with it,
instead of duplicating effort into IPv4. Especially because auto-
addressing for the ACP with IPv4 would be more complex than in IPv6
due to the IPv4 addressing space.
5. IANA Considerations
This document requests no action by IANA.
6. Acknowledgements
This work originated from an Autonomic Networking project at cisco
Systems, which started in early 2010 including customers involved in
the design and early testing. Many people contributed to the aspects
described in this document, including in alphabetical order: BL
Balaji, Steinthor Bjarnason, Yves Herthoghs, Sebastian Meissner, Ravi
Kumar Vadapalli. The author would also like to thank Michael
Richardson, James Woodyatt and Brian Carpenter for their review and
comments. Special thanks to Sheng Jiang and Mohamed Boucadair for
their thorough review.
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7. Change log [RFC Editor: Please remove]
04: Integrated fixes from Mohamed Boucadairs review.
03: Integrated fixes from Shepherd review (Sheng Jiang).
01: Refresh timeout. Stable document, change in author
association.
01: Refresh timeout. Stable document, no changes.
00: Changed title/dates.
individual-02: Updated references.
individual-03: Modified ULA text to not suggest ULA-C as much
better anymore, but still mention it.
individual-02: Added explanation why no IPv4 for ACP.
individual-01: Added security section discussing the role of
address prefix selection and DNS for ACP. Title change to
emphasize focus on OAM. Expanded abstract.
individual-00: Initial version.
8. References
[I-D.ietf-anima-autonomic-control-plane]
Behringer, M., Eckert, T., and S. Bjarnason, "An Autonomic
Control Plane (ACP)", draft-ietf-anima-autonomic-control-
plane-08 (work in progress), July 2017.
[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
S., and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
keyinfra-07 (work in progress), July 2017.
[I-D.ietf-anima-grasp]
Bormann, C., Carpenter, B., and B. Liu, "A Generic
Autonomic Signaling Protocol (GRASP)", draft-ietf-anima-
grasp-15 (work in progress), July 2017.
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[I-D.ietf-anima-reference-model]
Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L.,
Pierre, P., Liu, B., Nobre, J., and J. Strassner, "A
Reference Model for Autonomic Networking", draft-ietf-
anima-reference-model-04 (work in progress), July 2017.
[ITUT] International Telecommunication Union, "Architecture and
specification of data communication network",
ITU-T Recommendation G.7712/Y.1703, June 2008.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<http://www.rfc-editor.org/info/rfc4193>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
D., and S. Mansfield, "Guidelines for the Use of the "OAM"
Acronym in the IETF", BCP 161, RFC 6291,
DOI 10.17487/RFC6291, June 2011,
<http://www.rfc-editor.org/info/rfc6291>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.
[RFC6418] Blanchet, M. and P. Seite, "Multiple Interfaces and
Provisioning Domains Problem Statement", RFC 6418,
DOI 10.17487/RFC6418, November 2011,
<http://www.rfc-editor.org/info/rfc6418>.
[RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
Requirements", RFC 6434, DOI 10.17487/RFC6434, December
2011, <http://www.rfc-editor.org/info/rfc6434>.
[RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for
Routing Protocols (KARP) Design Guidelines", RFC 6518,
DOI 10.17487/RFC6518, February 2012,
<http://www.rfc-editor.org/info/rfc6518>.
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[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
<http://www.rfc-editor.org/info/rfc6824>.
[RFC7575] Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
Networking: Definitions and Design Goals", RFC 7575,
DOI 10.17487/RFC7575, June 2015,
<http://www.rfc-editor.org/info/rfc7575>.
Authors' Addresses
Toerless Eckert (editor)
Futurewei Technologies Inc.
2330 Central Expy
Santa Clara 95050
USA
Email: tte+ietf@cs.fau.de
Michael H. Behringer
Email: michael.h.behringer@gmail.com
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