ANIMA WG M. Behringer, Ed.
Internet-Draft S. Bjarnason
Intended status: Standards Track Balaji. BL
Expires: September 22, 2016 T. Eckert
Cisco Systems
March 21, 2016
An Autonomic Control Plane
draft-ietf-anima-autonomic-control-plane-02
Abstract
Autonomic functions need a control plane to communicate, which
depends on some addressing and routing. This Autonomic Control Plane
should ideally be self-managing, and as independent as possible of
configuration. This document defines an "Autonomic Control Plane",
with the primary use as a control plane for autonomic functions. It
also serves as a "virtual out of band channel" for OAM communications
over a network that is not configured, or mis-configured.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 22, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Use Cases for an Autonomic Control Plane . . . . . . . . . . 4
2.1. An Infrastructure for Autonomic Functions . . . . . . . . 4
2.2. Secure Bootstrap over an Unconfigured Network . . . . . . 4
2.3. Data Plane Independent Permanent Reachability . . . . . . 5
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Self-Creation of an Autonomic Control Plane . . . . . . . . . 8
5.1. Preconditions . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Candidate ACP Neighbor Selection . . . . . . . . . . . . 8
5.3. Capability Negotiation . . . . . . . . . . . . . . . . . 9
5.4. Channel Establishment . . . . . . . . . . . . . . . . . . 10
5.5. Context Separation . . . . . . . . . . . . . . . . . . . 10
5.6. Addressing inside the ACP . . . . . . . . . . . . . . . . 11
5.6.1. Fundamental Concepts of Autonomic Addressing . . . . 11
5.6.2. The Base Addressing Scheme . . . . . . . . . . . . . 12
5.6.3. Possible Sub-Schemes . . . . . . . . . . . . . . . . 13
5.6.4. Usage of the Zone Field . . . . . . . . . . . . . . . 14
5.7. Routing in the ACP . . . . . . . . . . . . . . . . . . . 15
6. Workarounds for Non-Autonomic Nodes . . . . . . . . . . . . . 16
6.1. Connecting a Non-Autonomic Controller / NMS system . . . 16
6.2. ACP through Non-Autonomic L3 Clouds . . . . . . . . . . . 16
7. Building the ACP . . . . . . . . . . . . . . . . . . . . . . 17
7.1. Neighbor discovery via GRASP . . . . . . . . . . . . . . 17
7.2. Channel Selection . . . . . . . . . . . . . . . . . . . . 17
7.3. Security Association protocols . . . . . . . . . . . . . 18
7.3.1. ACP via IPsec . . . . . . . . . . . . . . . . . . . . 18
7.3.2. ACP via GRE/IPsec . . . . . . . . . . . . . . . . . . 19
7.3.3. ACP via dTLS . . . . . . . . . . . . . . . . . . . . 19
7.3.4. GRASP/TLS negotiation . . . . . . . . . . . . . . . . 19
7.3.5. ACP Security Profiles . . . . . . . . . . . . . . . . 20
7.4. GRASP instance details . . . . . . . . . . . . . . . . . 20
8. Self-Healing Properties . . . . . . . . . . . . . . . . . . . 21
9. Self-Protection Properties . . . . . . . . . . . . . . . . . 22
10. The Administrator View . . . . . . . . . . . . . . . . . . . 22
11. Explanations . . . . . . . . . . . . . . . . . . . . . . . . 23
11.1. Why GRASP to discover autonomic neighbors . . . . . . . 23
12. Security Considerations . . . . . . . . . . . . . . . . . . . 24
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
15. Change log [RFC Editor: Please remove] . . . . . . . . . . . 26
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15.1. Initial version . . . . . . . . . . . . . . . . . . . . 26
15.2. draft-behringer-anima-autonomic-control-plane-00 . . . . 26
15.3. draft-behringer-anima-autonomic-control-plane-01 . . . . 26
15.4. draft-behringer-anima-autonomic-control-plane-02 . . . . 26
15.5. draft-behringer-anima-autonomic-control-plane-03 . . . . 27
15.6. draft-ietf-anima-autonomic-control-plane-00 . . . . . . 27
15.7. draft-ietf-anima-autonomic-control-plane-01 . . . . . . 27
15.8. draft-ietf-anima-autonomic-control-plane-02 . . . . . . 28
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
Appendix A. Background on the choice of routing protocol . . . . 29
Appendix B. Alternative: An ACP without Separation . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction
Autonomic Networking is a concept of self-management: Autonomic
functions self-configure, and negotiate parameters and settings
across the network. [RFC7575] defines the fundamental ideas and
design goals of Autonomic Networking. A gap analysis of Autonomic
Networking is given in [RFC7576]. The reference architecture for
Autonomic Networking in the IETF is currently being defined in the
document [I-D.behringer-anima-reference-model]
Autonomic functions need a stable and robust infrastructure to
communicate on. This infrastructure should be as robust as possible,
and it should be re-usable by all autonomic functions. [RFC7575]
calls it the "Autonomic Control Plane". This document defines the
Autonomic Control Plane.
Today, the management and control plane of networks typically runs in
the global routing table, which is dependent on correct configuration
and routing. Misconfigurations or routing problems can therefore
disrupt management and control channels. Traditionally, an out of
band network has been used to recover from such problems, or
personnel is sent on site to access devices through console ports.
However, both options are operationally expensive.
In increasingly automated networks either controllers or distributed
autonomic service agents in the network require a control plane which
is independent of the network they manage, to avoid impacting their
own operations.
This document describes options for a self-forming, self-managing and
self-protecting "Autonomic Control Plane" (ACP) which is inband on
the network, yet as independent as possible of configuration,
addressing and routing problems (for details how this achieved, see
Section 5). It therefore remains operational even in the presence of
configuration errors, addressing or routing issues, or where policy
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could inadvertently affect control plane connectivity. The Autonomic
Control Plane serves several purposes at the same time:
o Autonomic functions communicate over the ACP. The ACP therefore
supports directly Autonomic Networking functions, as described in
[I-D.behringer-anima-reference-model]. For example, GRASP
[I-D.ietf-anima-grasp] can run inside the ACP.
o An operator can use it to log into remote devices, even if the
data plane is misconfigured or unconfigured.
o A controller or network management system can use it to securely
bootstrap network devices in remote locations, even if the network
in between is not yet configured; no data-plane dependent
bootstrap configuration is required. An example of such a secure
bootstrap process is described in
[I-D.ietf-anima-bootstrapping-keyinfra]
This document describes some use cases for the ACP in Section 2, it
defines the requirements in Section 3, Section 4 gives an overview
how an Autonomic Control Plane is constructed, and in Section 5 the
detailed process is explained. Section 6 explains how non-autonomic
nodes and networks can be integrated, Section 7 defines the
negotiation protocol, and Section 7.3 the first channel types for the
ACP.
The document "Autonomic Network Stable Connectivity"
[I-D.eckert-anima-stable-connectivity] describes how the ACP can be
used to provide stable connectivity for OAM applications. It also
explains on how existing management solutions can leverage the ACP in
parallel with traditional management models, when to use the ACP
versus the data plane, how to integrate IPv4 based management, etc.
2. Use Cases for an Autonomic Control Plane
2.1. An Infrastructure for Autonomic Functions
Autonomic Functions need a stable infrastructure to run on, and all
autonomic functions should use the same infrastructure to minimise
the complexity of the network. This way, there is only need for a
single discovery mechanism, a single security mechanism, and other
processes that distributed functions require.
2.2. Secure Bootstrap over an Unconfigured Network
Today, bootstrapping a new device typically requires all devices
between a controlling node (such as an SDN controller) and the new
device to be completely and correctly addressed, configured and
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secured. Therefore, bootstrapping a network happens in layers around
the controller. Without console access (for example through an out
of band network) it is not possible today to make devices securely
reachable before having configured the entire network between.
With the ACP, secure bootstrap of new devices can happen without
requiring any configuration on the network. A new device can
automatically be bootstrapped in a secure fashion and be deployed
with a domain certificate. This does not require any configuration
on intermediate nodes, because they can communicate through the ACP.
2.3. Data Plane Independent Permanent Reachability
Today, most critical control plane protocols and network management
protocols are running in the data plane (global routing table) of the
network. This leads to undesirable dependencies between control and
management plane on one side and the data plane on the other: Only if
the data plane is operational, will the other planes work as
expected.
Data plane connectivity can be affected by errors and faults, for
example certain AAA misconfigurations can lock an administrator out
of a device; routing or addressing issues can make a device
unreachable; shutting down interfaces over which a current management
session is running can lock an admin irreversibly out of the device.
Traditionally only console access can help recover from such issues.
Data plane dependencies also affect NOC/SDN controller applications:
Certain network changes are today hard to operate, because the change
itself may affect reachability of the devices. Examples are address
or mask changes, routing changes, or security policies. Today such
changes require precise hop-by-hop planning.
The ACP provides reachability that is largely independent of the data
plane, which allows control plane and management plane to operate
more robustly:
o For management plane protocols, the ACP provides the functionality
of a "Virtual-out-of-band (VooB) channel", by providing
connectivity to all devices regardless of their configuration or
global routing table.
o For control plane protocols, the ACP allows their operation even
when the data plane is temporarily faulty, or during transitional
events, such as routing changes, which may affect the control
plane at least temporarily. This is specifically important for
autonomic service agents, which could affect data plane
connectivity.
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The document "Autonomic Network Stable Connectivity"
[I-D.eckert-anima-stable-connectivity] explains the use cases for the
ACP in significantly more detail and explains how the ACP can be used
in practical network operations.
3. Requirements
The Autonomic Control Plane has the following requirements:
1. The ACP SHOULD provide robust connectivity: As far as possible,
it should be independent of configured addressing, configuration
and routing. Requirements 2 and 3 build on this requirement, but
also have value on their own.
2. The ACP MUST have a separate address space from the data plane.
Reason: traceability, debug-ability, separation from data plane,
security (can block easily at edge).
3. The ACP MUST use autonomically managed address space. Reason:
easy bootstrap and setup ("autonomic"); robustness (admin can't
mess things up so easily). This document suggests to use ULA
addressing for this purpose.
4. The ACP MUST be generic. Usable by all the functions and
protocols of the AN infrastructure. It MUST NOT be tied to a
particular protocol.
5. The ACP MUST provide security: Messages coming through the ACP
MUST be authenticated to be from a trusted node, and SHOULD (very
strong SHOULD) be encrypted.
The default mode of operation of the ACP is hop-by-hop, because this
interaction can be built on IPv6 link local addressing, which is
autonomic, and has no dependency on configuration (requirement 1).
It may be necessary to have end-to-end connectivity in some cases,
for example to provide an end-to-end security association for some
protocols. This is possible, but then has a dependency on routable
address space.
4. Overview
The Autonomic Control Plane is constructed in the following way (for
details, see Section 5):
o An autonomic node creates a virtual routing and forwarding (VRF)
instance, or a similar virtual context.
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o It determines, following a policy, a candidate peer list. This is
the list of nodes to which it should establish an autonomic
control plane. Default policy is: To all adjacent nodes in the
same domain. Intent can override this default policy.
o For each node in the candidate peer list, it authenticates that
node and negotiates a mutually acceptable channel type.
o It then establishes a secure tunnel of the negotiated channel
type. These tunnels are placed into the previously set up VRF.
This creates an overlay network with hop-by-hop tunnels.
o Inside the ACP VRF, each node sets up a virtual interface with its
ULA IPv6 address.
o Each node runs a lightweight routing protocol, to announce
reachability of the virtual addresses inside the ACP.
o Non-autonomic NMS systems or controllers have to be manually
connected into the ACP.
o Connecting over non-autonomic Layer-3 clouds initially requires a
tunnel between autonomic nodes.
o None of the above operations (except manual ones) is reflected in
the configuration of the device.
The following figure illustrates the ACP.
autonomic node 1 autonomic node 2
................... ...................
secure . . secure . . secure
tunnel : +-----------+ : tunnel : +-----------+ : tunnel
..--------| ACP VRF |---------------------| ACP VRF |---------..
: / \ / \ <--routing--> / \ / \ :
: \ / \ / \ / \ / :
..--------| virtual |---------------------| virtual |---------..
: | interface | : : | interface | :
: +-----------+ : : +-----------+ :
: : : :
: data plane :...............: data plane :
: : link : :
:.................: :.................:
Figure 1
The resulting overlay network is normally based exclusively on hop-
by-hop tunnels. This is because addressing used on links is IPv6
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link local addressing, which does not require any prior set-up. This
way the ACP can be built even if there is no configuration on the
devices, or if the data plane has issues such as addressing or
routing problems.
5. Self-Creation of an Autonomic Control Plane
This section describes the steps to set up an Autonomic Control
Plane, and highlights the key properties which make it
"indestructible" against many inadvert changes to the data plane, for
example caused by misconfigurations.
5.1. Preconditions
An autonomic node can be a router, switch, controller, NMS host, or
any other IP device. We assume an autonomic node has:
o A globally unique domain certificate, with which it can
cryptographically assert its membership of the domain. The
document [I-D.ietf-anima-bootstrapping-keyinfra] describes how a
domain certificate can be automatically and securely derived from
a vendor specific Unique Device Identifier (UDI) or IDevID
certificate. (Note the UDI used in this document is NOT the UUID
specified in [RFC4122].)
o An adjacency table, which contains information about adjacent
autonomic nodes, at a minimum: node-ID, IP address, domain,
certificate. An autonomic device maintains this adjacency table
up to date. Where the next autonomic device is not directly
adjacent, the information in the adjacency table can be
supplemented by configuration. For example, the node-ID and IP
address could be configured.
The adjacency table MAY contain information about the validity and
trust of the adjacent autonomic node's certificate. However,
subsequent steps MUST always start with authenticating the peer.
The adjacency table contains information about adjacent autonomic
nodes in general, independently of their domain and trust status.
The next step determines to which of those autonomic nodes an ACP
connection should be established.
5.2. Candidate ACP Neighbor Selection
An autonomic node must determine to which other autonomic nodes in
the adjacency table it should build an ACP connection.
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The ACP is by default established exclusively between nodes in the
same domain.
Intent can change this default behaviour. The precise format for
this Intent needs to be defined outside this document. Example
Intent policies are:
o The ACP should be built between all sub-domains for a given parent
domain. For example: For domain "example.com", nodes of
"example.com", "access.example.com", "core.example.com" and
"city.core.example.com" should all establish one single ACP.
o Two domains should build one single ACP between themselves, for
example "example1.com" should establish the ACP also with nodes
from "example2.com". For this case, the two domains must be able
to validate their trust, typically by cross-signing their
certificate infrastructure.
The result of the candidate ACP neighbor selection process is a list
of adjacent or configured autonomic neighbors to which an ACP channel
should be established. The next step begins that channel
establishment.
5.3. Capability Negotiation
Autonomic devices may have different capabilities based on the type
of device, OS version, etc. To establish a trusted secure ACP
channel, devices must first negotiate their mutual capabilities in
the data plane. This allows for the support of different channel
types in the future.
For each node on the candidate ACP neighbor list, capabilities need
to be exchanged. The capability negotiation is based on GRASP
[I-D.ietf-anima-grasp]. The relevant protocol details are defined in
Section 7. This negotiation MUST be secure: The identity of the
other node MUST be validated during capability negotiation, and the
exchange MUST be authenticated.
The first parameter to be negotiated is the ACP Channel type. The
channel types are defined in Section 7.3. Other parameters may be
added later.
Intent may also influence the capability negotiation. For example,
Intent may require a minimum ACP tunnel security. This is outside
scope for this document.
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5.4. Channel Establishment
After authentication and capability negotiation autonomic nodes
establish a secure channel towards the AN neighbors with the above
negotiated parameters.
The channel establishment MUST be authenticated. Whether or not, and
how, a channel is encrypted is part of the capability negotiation,
potentially controlled by Intent.
In order to be independent of configured link addresses, channels
SHOULD use IPv6 link local addresses between adjacent neighbors
wherever possible. This way, the ACP tunnels are independent of
correct network wide routing.
Since channels are by default established between adjacent neighbors,
the resulting overlay network does hop by hop encryption. Each node
decrypts incoming traffic from the ACP, and encrypts outgoing traffic
to its neighbors in the ACP. Routing is discussed in Section 5.7.
If two nodes are connected via several links, the ACP SHOULD be
established on every link, but it is possible to establish the ACP
only on a sub-set of links. Having an ACP channel on every link has
a number of advantages, for example it allows for a faster failover
in case of link failure, and it reflects the physical topology more
closely. Using a subset of links (for example, a single link),
reduces resource consumption on the devices, because state needs to
be kept per ACP channel.
5.5. Context Separation
The ACP is in a separate context from the normal data plane of the
device. This context includes the ACP channels IPv6 forwarding and
routing as well as any required higher layer ACP functions.
In classical network device platforms, a dedicated so called "Virtual
routing and forwarding instance" (VRF) is one logical implementation
option for the ACP. If possible by the platform SW architecture,
separation options that minimize shared components are preferred.
The context for the ACP needs to be established automatically during
bootstrap of a device. As much as possible it should be protected
from being modified unintentionally by data plane configuration.
Context separation improves security, because the ACP is not
reachable from the global routing table. Also, configuration errors
from the data plane setup do not affect the ACP.
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[EDNOTE: Previous versions of this document also discussed an option
where the ACP runs in the data plane without logical separation.
Consensus is to focus only on the separated ACP now, and to remove
the ACP in the data plane from this document. See Appendix B for the
reasons for this decision.]
5.6. Addressing inside the ACP
The channels explained above typically only establish communication
between two adjacent nodes. In order for communication to happen
across multiple hops, the autonomic control plane requires internal
network wide valid addresses and routing. Each autonomic node must
create a virtual interface with a network wide unique address inside
the ACP context mentioned in Section 5.5. This address may be used
also in other virtual contexts.
With the algorithm introduced here, all autonomic devices in the same
domain have the same /48 prefix. Conversely, global IDs from
different domains are unlikely to clash, such that two networks can
be merged, as long as the policy allows that merge. See also
Section 8 for a discussion on merging domains.
Links inside the ACP only use link-local IPv6 addressing, such that
each node only requires one routable virtual address.
5.6.1. Fundamental Concepts of Autonomic Addressing
o Usage: Autonomic addresses are exclusively used for self-
management functions inside a trusted domain. They are not used
for user traffic. Communications with entities outside the
trusted domain use another address space, for example normally
managed routable address space.
o Separation: Autonomic address space is used separately from user
address space and other address realms. This supports the
robustness requirement.
o Loopback-only: Only loopback interfaces of autonomic nodes carry a
routable address; all other interfaces exclusively use IPv6 link
local for autonomic functions. The usage of IPv6 link local
addressing is discussed in [RFC7404].
o Use-ULA: For loopback interfaces of autonomic nodes, we use Unique
Local Addresses (ULA), as specified in [RFC4193]. An alternative
scheme was discussed, using assigned ULA addressing. The
consensus was to use standard ULA, because it was deemed to be
sufficient.
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o No external connectivity: They do not provide access to the
Internet. If a node requires further reaching connectivity, it
should use another, traditionally managed address scheme in
parallel.
The ACP is based exclusively on IPv6 addressing, for a variety of
reasons:
o Simplicity, reliability and scale: If other network layer
protocols were supported, each would have to have its own set of
security associations, routing table and process, etc.
o Autonomic functions do not require IPv4: Autonomic functions and
autonomic service agents are new concepts. They can be
exclusively built on IPv6 from day one. There is no need for
backward compatibility.
o OAM protocols no not require IPv4: The ACP may carry OAM
protocols. All relevant protocols (SNMP, TFTP, SSH, SCP, Radius,
Diameter, ...) are available in IPv6.
5.6.2. The Base Addressing Scheme
The Base ULA addressing scheme for autonomic nodes has the following
format:
8 40 3 77
+--+--------------+------+------------------------------------------+
|FD| hash(domain) | Type | (sub-scheme) |
+--+--------------+------+------------------------------------------+
Figure 2: Base Addressing Scheme
The first 48 bits follow the ULA scheme, as defined in [RFC4193], to
which a type field is added:
o "FD" identifies a locally defined ULA address.
o The "global ID" is set here to be a hash of the domain name, which
results in a pseudo-random 40 bit value. It is calculated as the
first 40 bits of the MD5 hash of the domain name, in the example
"example.com".
o Type: Set to 000 (3 zero bits). This field allows different
address sub-schemes in the future. The goal is to start with a
minimal number (ideally one) of sub-schemes initially, but to
allow for extensions later if and when required. This addresses
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the "upgradability" requirement. Assignment of types for this
field should be maintained by IANA.
5.6.3. Possible Sub-Schemes
The sub-schemes listed here are not intended to be all supported
initially, but are listed for discussion. The final document should
define ideally only a single sub-scheme for now, and leave the other
"types" for later assignment.
5.6.3.1. Sub-Scheme 1
51 13 64
+------------------------+---------+--------------------------------+
| (base scheme) | Zone ID | Device ID |
+------------------------+---------+--------------------------------+
Figure 3: Addressing Scheme 1
The fields are defined as follows: [Editor's note: The lengths of the
fields is for discussion.]
o Zone ID: If set to all zero bits: The device ID bits are used as
an identifier (as opposed to a locator). This results in a non-
hierarchical, flat addressing scheme. Any other value indicates a
zone. See section Section 5.6.4 on how this field is used in
detail.
o Device ID: A unique value for each device.
The device ID is derived as follows: In an Autonomic Network, a
registrar is enrolling new devices. As part of the enrolment process
the registrar assigns a number to the device, which is unique for
this registrar, but not necessarily unique in the domain. The 64 bit
device ID is then composed as:
o 48 bit: Registrar ID, a number unique inside the domain that
identifies the registrar which assigned the name to the device. A
MAC address of the registrar can be used for this purpose.
o 16 bit: Device number, a number which is unique for a given
registrar, to identify the device. This can be a sequentially
assigned number.
The "device ID" itself is unique in a domain (i.e., the Zone-ID is
not required for uniqueness). Therefore, a device can be addressed
either as part of a flat hierarchy (zone ID = 0), or with an
aggregation scheme (any other zone ID). A address with zone-ID could
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be interpreted as an identifier, with another zone-ID as a locator.
See Section 5.6.4 for a description of the zone bits.
5.6.3.2. Sub-Scheme 2
51 13 64-V ?
+------------------------+---------+----------------------------+---+
| (base scheme) | Zone ID | Device ID | V |
+------------------------+---------+----------------------------+---+
Figure 4: Addressing Scheme 2
The fields are defined as follows: [Editor's note: The lengths of the
fields is for discussion.]
o Zone ID: As in sub-scheme 1.
o Device ID: As in sub-scheme 1.
o V: Virtualization bit(s): 1 or more bits that indicate a virtual
context on an autonomic node.
In addition the scheme 1 (Section 5.6.3.1), this scheme allows the
direct addressing of specific virtual containers / VMs on an
autonomic node. An increasing number of hardware platforms have a
distributed architecture, with a base OS for the node itself, and the
support for hardware blades with potentially different OSs. The VMs
on the blades could be considered as separate autonomic nodes, in
which case it would make sense to be able to address them directly.
Autonomic Service Agents (ASAs) could be instantiated in either the
base OS, or one of the VMs on a blade. This addressing scheme allows
for the easy separation of the hardware context.
The location of the V bit(s) at the end of the address allows to
announce a single prefix for each autonomic node, while having
separate virtual contexts addressable directly.
5.6.4. Usage of the Zone Field
The "zone ID" allows for the introduction of structure in the
addressing scheme.
Zone = zero is the default addressing scheme in an autonomic domain.
Every autonomic node MUST respond to its ACP address with zone=0.
Used on its own this leads to a non-hierarchical address scheme,
which is suitable for networks up to a certain size. In this case,
the addresses primarily act as identifiers for the nodes, and
aggregation is not possible.
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If aggregation is required, the 13 bit value allows for up to 8191
zones. The allocation of zone numbers may either happen
automatically through a to-be-defined algorithm; or it could be
configured and maintained manually. [We could divide the zone space
into manual and automatic space - to be discussed.]
If a device learns through an autonomic method or through
configuration that it is part of a zone, it MUST also respond to its
ACP address with that zone number. In this case the ACP loopback is
configured with two ACP addresses: One for zone 0 and one for the
assigned zone. This method allows for a smooth transition between a
flat addressing scheme and an hierarchical one.
(Theoretically, the 13 bits for the zone ID would allow also for two
levels of zones, introducing a sub-hierarchy. We do not think this
is required at this point, but a new type could be used in the future
to support such a scheme.)
Note: Another way to introduce hierarchy is to use sub-domains in the
naming scheme. The node names "node17.subdomainA.example.com" and
"node4.subdomainB.example.com" would automatically lead to different
ULA prefixes, which can be used to introduce a routing hierarchy in
the network, assuming that the subdomains are aligned with routing
areas.
5.7. Routing in the ACP
Once ULA address are set up all autonomic entities should run a
routing protocol within the autonomic control plane context. This
routing protocol distributes the ULA created in the previous section
for reachability. The use of the autonomic control plane specific
context eliminates the probable clash with the global routing table
and also secures the ACP from interference from the configuration
mismatch or incorrect routing updates.
The establishment of the routing plane and its parameters are
automatic and strictly within the confines of the autonomic control
plane. Therefore, no manual configuration is required.
All routing updates are automatically secured in transit as the
channels of the autonomic control plane are by default secured.
The routing protocol inside the ACP should be light weight and highly
scalable to ensure that the ACP does not become a limiting factor in
network scalability. We suggest the use of RPL [RFC6550] as one such
protocol which is light weight and scales well for the control plane
traffic. See Appendix A for more details on the choice of RPL.
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6. Workarounds for Non-Autonomic Nodes
6.1. Connecting a Non-Autonomic Controller / NMS system
The Autonomic Control Plane can be used by management systems, such
as controllers or network management system (NMS) hosts (henceforth
called simply "NMS hosts"), to connect to devices through it. For
this, an NMS host must have access to the ACP. By default, the ACP
is a self-protecting overlay network, which only allows access to
trusted systems. Therefore, a traditional, non-autonomic NMS system
does not have access to the ACP by default, just like any other
external device.
If the NMS host is not autonomic, i.e., it does not support autonomic
negotiation of the ACP, then it can be brought into the ACP by
explicit configuration. On an adjacent autonomic node with ACP, the
interface with the NMS host can be configured to be part of the ACP.
In this case, the NMS host is with this interface entirely and
exclusively inside the ACP. It would likely require a second
interface for connections between the NMS host and administrators, or
Internet based services. This mode of connecting an NMS host has
security consequences: All systems and processes connected to this
implicitly trusted interface have access to all autonomic nodes on
the entire ACP, without further authentication. Thus, this
connection must be physically controlled.
The non-autonomic NMS host must be routed in the ACP. This involves
two parts: 1) the NMS host must point default to the AN device for
the ULA prefix used inside the ACP, and 2) the prefix used between AN
node and NMS host must be announced into the ACP, and distributed
there.
The document "Autonomic Network Stable Connectivity"
[I-D.eckert-anima-stable-connectivity] explains in more detail how
the ACP can be integrated in a mixed NOC environment.
6.2. ACP through Non-Autonomic L3 Clouds
Not all devices in a network may be autonomic. If non-autonomic
Layer-2 devices are between autonomic nodes, the communications
described in this document should work, since it is IP based.
However, non-autonomic Layer-3 devices do not forward link local
autonomic messages, and thus break the Autonomic Control Plane.
One workaround is to manually configure IP tunnels between autonomic
nodes across a non-autonomic Layer-3 cloud. The tunnels are
represented on each autonomic node as virtual interfaces, and all
autonomic transactions work across such tunnels.
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Such manually configured tunnels are less "indestructible" than an
automatically created ACP based on link local addressing, since they
depend on correct data plane operations, such as routing and
addressing.
7. Building the ACP
7.1. Neighbor discovery via GRASP
Autonomic devices use inscure GRASP to discovery candidate autonomic
neighbors across L2 adjacencies. When Alice discovers Bob:
o If Alice is not part an autonomic domain, she starts autonomic
enrollment with Bob as the proxy using procedures described in
[I-D.ietf-anima-bootstrapping-keyinfra].
o If Alice is part of an autonomic domain, Alice attempts to build
the ACP to Bob. Bob will do the same.
7.2. Channel Selection
To avoid attacks, initial discovery of candidate ACP peers can not
include any non-protected negotiation. To avoid re-inventing and
validating security association mechanisms, the next step after
discoving the address of a candidate neighbor can only be to try
first to establish a security association with that neighbor using a
well-known security association method.
At this time in the lifecycle of autonomic devices, it is unclear
whether it is feasible to even decide on a single MTI (mandatory to
implement) security association protocol across all autonomic
devices.
From the use-cases it is clear that not all type of autonomic devices
can or need to connect directly to each other or are able to support
or prefer all possible mechanisms. For example, code space limited
IoT devices may only support dTLS (because that code exists already
on them for end-to-end security use-cases), but low-end in-ceiling L2
switches may only want to support MacSec because that is also
supported in HW, and only a more flexible garteway device may need to
support both of these mechanisms and potentially more.
To support these requirements, and make ACP channel negotiation also
easily extensible, the secure channel selection between Alice and Bob
is a potentially two stage process. In the first stage, Alice and
Bob directly try to establish a secure channel using the security-
association and channel protocols they support. One or more of these
protocols may simply be protocols not directly resulting in an ACP
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channel, but instead establishing a secure negotiation channel
through which the final secure channel protocol is decided. If both
Alice and Bob support such a negotiation step, then this secured
negotiation channel is the first step, and the secure channel
protocol is the second step.
If Alice supports multiple security association protocols in the
first step, it is a matter of Alices local policy to determine the
order in which she will try to build the connection to Bob. To
support multiple security association protocols, Alice must be able
to simultaneously act as a responder in parallel for all of them - so
that she can respond to any order in which Bob wants to prefer
building the security association.
When ACP setup between Alice and Bob results in the first secure
association to be established, the peer with the higher Device-ID in
the certificate will stop building new security associations. The
peer with the lower certificate Device-ID is now responsible to
continue building its most preferred security association and to tear
down all but that most preferred one - unless the secure association
is one of a negotation protocols whose rules superceed this.
All this negotiation is in the context of an "L2 interface". Alice
and Bob will build ACP connections to each other on every "L2
interface" that they both connect to.
7.3. Security Association protocols
The following sections define the security association protocols that
we consider to be important and feasible to specify in this document.
In all cases, the mutual authentication is done via the autonomic
domain certificate of the peer as follows - unless superceeded by
intent:
o The certificate is valid as proven by the security associations
protocol exchanges.
o The peers certificate is signed by the same CA as the devices
domain certificate.
o The peers OU (Organizational Unit) field in the certificates
Subject is the same as in the devices certificate.
7.3.1. ACP via IPsec
To run ACP via IPsec transport mode, no further IANA assignments/
definitions are required. All autonomic devices suppoting IPsec MUST
support IPsec security setup via IKEv2, transpoort mode encapsulation
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via the device and peer link-local IPv6 addresses and AES256
encryption. Further parameter options can be negotiated via IKEv2 or
via GRASP/TLS.
7.3.2. ACP via GRE/IPsec
In network devices it is often easier to provide virtual interfaces
on top of GRE encapsulation than natively on top of a simple IPsec
association. On those devices it may be necessary to run the ACP
secure channel on top of a GRE connection protected by the IPsec
association. The requirements for the IPsec association are the same
as described above, but instead of directly carrying the ACP IPv6
packets, the payload is an ACP IPv6 packet inside GREP/IPv6.
Note that without explicit negotiation (eg: via GRASP/TLS), this
method is incompatible to direct ACP via IPsec, so it must only be
used as an option during GRASP/TLS negotiation.
7.3.3. ACP via dTLS
To run ACP via UDP and dTLS v1.2 [RFC6347] an IANA assigned port
[TBD] is used. All autonomic devices supporting ACP via dTLS must
support AES256 encryption.
7.3.4. GRASP/TLS negotiation
To explicitly allow negotiation of the ACP channel protocol, GRASP
over a TLS connection using the GRASP_LISTEN_PORT and the devices and
peers link-local IPv6 address is used. When Alice and Bob support
GRASP negotiation, they do prefer it over any other non-explicitly
negotiated security association protocol and should wait trying any
non-negotiated ACP channel protocol until after it is clear that
GRASP/TLS will not work to the peer.
When Alice and Bob successfully establish the GRASP/TSL session, they
will initially negotiate the channel mechanism to use. Bob and Alice
each have a list of channel mehanisms they support, sorted by
preference. They negotiate the best mechansm supported by both of
them. In the absence of Intent, the mechanism choosen is the best
one for the device with the lower Device-ID.
After agreeing on a channel mechanism, Alice and Bob start the
selected Channel protocol. The GRASP/TLS connection can be kept
alive or timed out as long as the seelected channel protocol has a
secure association between Alice and Bob. When it terminates, it
needs to be re-negotiated via GRASP/TLS.
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Negotiation of a channel type may require IANA assignments of code
points. See IANA Considerations (Section 13) for the formal
definition of those code points.
TBD: The exact negotiation steps in GRASP to achieve this outcome.
7.3.5. ACP Security Profiles
A baseline autonomic device MUST support IPsec and SHOULD support
GRASP/TLS and dTLS. A constrained autonomic device MUST support
dTLS.
Autonomic devices need to specify in documentation the set of secure
ACP mechanisms they suppport.
7.4. GRASP instance details
GRASP run to (insecurely) discover autonomic neighbors are isolated
instances from each other and other uses of GRASP - GRASP/TLS
sessions of L2 interfaces and GRASP inside the ACP
Received GRASP packets are assigned to an instance of GRASP by the
context they are received on:
o GRASP packets received on an ACP (virtual) interfaces are assigned
to the ACP instance of GRASP
o GRASP/UDP packets received on L2 interfaces where the device is
willing to run ACP across are are assigned to a separate instance
of GRASP for that L2 interface. We call those instances of GRASP
the "insecure L2 GRASP instances" and the ASA to perform the
discovery the "insecure L2 discovery ASA" (IL2D).
o GRASP packets received inside a TLS connection established for
GRASP/TLS ACP negotiation are assigned to a separate instance of
GRASP for that negotiation
All insecure L2 discovery of candidate ACP neighbors via GRASP and
the potentially following GRASP/TLS negotiation is per-L2 interface:
If Alice and Bob connect to each other via multiple interfaces, they
will independently establish the ACP to each other across each of
these interfaces.
For every L2-discovery instance of GRASP and its IL2D, the following
rules apply, amending and overriding the recommendations in
[I-D.ietf-anima-grasp]:
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o GRASP link-local multicast discovery messages MUST use GTSM
[RFC5082]. With GTSM, discovery packets are sent with a TTL of
255 and packets received with a TTL smaller than 255 are ignored
upon receipt.
o The GRASP loop count of GRASP discovery packets must be set to 1
on sending.
o GRASP MUST send response messages for the discovery objected
defined here (overriding the MAY).
o GRASP MUST NOT respond to discovery objectives with the Divert
option - objectives learned and cached are solely for local
consumption.
o GRASP MUST NOT relay discovery or any other messages across
different interfaces.
TBD: The Details of the GRASP objective/packet formats still need to
be defined. Eg: Need to define an allocation for the objective of
"Autonomic Node".
8. Self-Healing Properties
The ACP is self-healing:
o New neighbors will automatically join the ACP after successful
validation and will become reachable using their unique ULA
address across the ACP.
o When any changes happen in the topology, the routing protocol used
in the ACP will automatically adapt to the changes and will
continue to provide reachability to all devices.
o If an existing device gets revoked, it will automatically be
denied access to the ACP as its domain certificate will be
validated against a Certificate Revocation List during
authentication. Since the revocation check is only done at the
establishment of a new security association, existing ones are not
automatically torn down. If an immediate disconnect is required,
existing sessions to a freshly revoked device can be re-set.
The ACP can also sustain network partitions and mergers. Practically
all ACP operations are link local, where a network partition has no
impact. Devices authenticate each other using the domain
certificates to establish the ACP locally. Addressing inside the ACP
remains unchanged, and the routing protocol inside both parts of the
ACP will lead to two working (although partitioned) ACPs.
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There are few central dependencies: A certificate revocation list
(CRL) may not be available during a network partition; a suitable
policy to not immediately disconnect neighbors when no CRL is
available can address this issue. Also, a registrar or Certificate
Authority might not be available during a partition. This may delay
renewal of certificates that are to expire in the future, and it may
prevent the enrolment of new devices during the partition.
After a network partition, a re-merge will just establish the
previous status, certificates can be renewed, the CRL is available,
and new devices can be enrolled everywhere. Since all devices use
the same trust anchor, a re-merge will be smooth.
Merging two networks with different trust anchors requires the trust
anchors to mutually trust each other (for example, by cross-signing).
As long as the domain names are different, the addressing will not
overlap (see Section 5.6).
9. Self-Protection Properties
As explained in Section 5, the ACP is based on channels being built
between devices which have been previously authenticated based on
their domain certificates. The channels themselves are protected
using standard encryption technologies like DTLS or IPsec which
provide additional authentication during channel establishment, data
integrity and data confidentiality protection of data inside the ACP
and in addition, provide replay protection.
An attacker will therefore not be able to join the ACP unless having
a valid domain certificate, also packet injection and sniffing
traffic will not be possible due to the security provided by the
encryption protocol.
The remaining attack vector would be to attack the underlying AN
protocols themselves, either via directed attacks or by denial-of-
service attacks. However, as the ACP is built using link-local IPv6
address, remote attacks are impossible. The ULA addresses are only
reachable inside the ACP context, therefore unreachable from the data
plane. Also, the ACP protocols should be implemented to be attack
resistant and not consume unnecessary resources even while under
attack.
10. The Administrator View
An ACP is self-forming, self-managing and self-protecting, therefore
has minimal dependencies on the administrator of the network.
Specifically, since it is independent of configuration, there is no
scope for configuration errors on the ACP itself. The administrator
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may have the option to enable or disable the entire approach, but
detailed configuration is not possible. This means that the ACP must
not be reflected in the running configuration of devices, except a
possible on/off switch.
While configuration is not possible, an administrator must have full
visibility of the ACP and all its parameters, to be able to do
trouble-shooting. Therefore, an ACP must support all show and debug
options, as for any other network function. Specifically, a network
management system or controller must be able to discover the ACP, and
monitor its health. This visibility of ACP operations must clearly
be separated from visibility of data plane so automated systems will
never have to deal with ACP aspect unless they explicitly desire to
do so.
Since an ACP is self-protecting, a device not supporting the ACP, or
without a valid domain certificate cannot connect to it. This means
that by default a traditional controller or network management system
cannot connect to an ACP. See Section 6.1 for more details on how to
connect an NMS host into the ACP.
11. Explanations
This section is non-normative and intended to provide further
explanations for the choices made in this document.
11.1. Why GRASP to discover autonomic neighbors
None of the considered mechanisms to establish security associations
(eg: IPsec or dTLS) include mechanisms to discover candidate
neighbors, so these security mechanisms themselves are insufficient
for the discovery.
Existing L2 mechanisms such as LLDP (or vendor speccific alternatives
like Ciscos CDP) are L2 link-local. If an autonomic device connects
via an LLDP capable, but non-autonomic capable L2 switch to another
autonomic device, then the non-autonomic L2 switch would not
propagate the LLDP messages, so discovery would not work as desired.
Existing L3/L4 link local discovery mechanisms such as mDNS or Web-
Services Discovery (http://specs.xmlsoap.org/ws/2005/04/discovery/ws-
discovery.pdf) are capable to support the simple discovery required
by autonomic devices but have the following downsides compared to
GRASP.
There is no clear single ubiquitoous protocol that would apply
equally well to all market segments in which autonomic routers are
intended to be deployed. Making a choice is therefore difficult.
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In some of these protocols, the fact that they operate L3 link local
is often seen as a limitation rather than as a necessity for the
application.
Various mechanisms are used or considered in these protocols to
expand the scope of discovery beyond a single L3 subnet. If
autonomic devices would use such a protocol, then autonomic discovery
messages could more likely leak into remote networks and give more
undesired (insecured) visibility into the presence of autonomic
devices and potentially leading to more attempts to establish
autonomic associations with those discovered devices. To achieve the
maximum resilience with the minimum number of ACP channels, those
channels need to follow as closely the physcial hops in the topology
as possible.
Visibility of discovery protocols in other domains may be
undesirable: Visibility of mDNS messages for example could extend all
the way into end user application level service browsers. It is
undesirable to see desvices announcing themselves as automic there.
Existing protocols can be more complex compared to GRASP as they have
been designed for different purposes, for example to be more flexible
and generic. In mDNS, if DNS-SD was used, it would require at least
four RRs to be exchanged for a single service: a PTR, a SRV, a TXT
and a AAAA RR. Minimizing the number of protocol exchanges by
coalescing these RRs is possible but requires additional software
design considerations.
GRASP is already required inside the ACP and a highly desirable
option for secure ACP channel negotiation (GRASP/TLS). Using it for
discovery allows to reuse that already necessary code basis. If any
other protocol was used for discovery, then autonomic discovery might
be the only purpose for which the protocol code exists in the device.
None of the above arguments individually are strong reasons not to
use one of these GRASP alternatives, but together they make it
reasonable to first define GRASP as the MTI (Mandatory To Implement)
for the discovery step.
12. Security Considerations
An ACP is self-protecting and there is no need to apply configuration
to make it secure. Its security therefore does not depend on
configuration.
However, the security of the ACP depends on a number of other
factors:
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o The usage of domain certificates depends on a valid supporting PKI
infrastructure. If the chain of trust of this PKI infrastructure
is compromised, the security of the ACP is also compromised. This
is typically under the control of the network administrator.
o Security can be compromised by implementation errors (bugs), as in
all products.
Fundamentally, security depends on correct operation, implementation
and architecture. Autonomic approaches such as the ACP largely
eliminate the dependency on correct operation; implementation and
architectural mistakes are still possible, as in all networking
technologies.
13. IANA Considerations
Section 7.3.3 describes ACP over dTLS, which requires a well-known
UDP port. We request IANA to assign this UDP port for 'ACP over
dTLS'.
Section 7.3.4 describes an option for the channel negotiation, the
'ACP channel type'. We request IANA to create a registry for 'ACP
channel type'.
The ACP channel type is a 8-bit unsigned integer. This document only
assigns the first value.
Number | Channel Type | RFC
---------+-----------------------------------+------------
0 | GRE tunnel protected with | this document
| IPsec transport mode |
1-255 | reserved for future channel types |
Section 5.6.2 describes a 'type' field in the base addressing scheme.
We request IANA to create a registry for the 'ACP addressing scheme
type'. The initial value and definition will be determined in a
later version of this document.
14. Acknowledgements
This work originated from an Autonomic Networking project at Cisco
Systems, which started in early 2010. Many people contributed to
this project and the idea of the Autonomic Control Plane, amongst
which (in alphabetical order): Ignas Bagdonas, Parag Bhide, Alex
Clemm, Yves Hertoghs, Bruno Klauser, Max Pritikin, Ravi Kumar
Vadapalli.
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Further input and suggestions were received from: Rene Struik, Brian
Carpenter, Benoit Claise.
15. Change log [RFC Editor: Please remove]
15.1. Initial version
First version of this document:
[I-D.behringer-autonomic-control-plane]
15.2. draft-behringer-anima-autonomic-control-plane-00
Initial version of the anima document; only minor edits.
15.3. draft-behringer-anima-autonomic-control-plane-01
o Clarified that the ACP should be based on, and support only IPv6.
o Clarified in intro that ACP is for both, between devices, as well
as for access from a central entity, such as an NMS.
o Added a section on how to connect an NMS system.
o Clarified the hop-by-hop crypto nature of the ACP.
o Added several references to GDNP as a candidate protocol.
o Added a discussion on network split and merge. Although, this
should probably go into the certificate management story longer
term.
15.4. draft-behringer-anima-autonomic-control-plane-02
Addresses (numerous) comments from Brian Carpenter. See mailing list
for details. The most important changes are:
o Introduced a new section "overview", to ease the understanding of
the approach.
o Merged the previous "problem statement" and "use case" sections
into a mostly re-written "use cases" section, since they were
overlapping.
o Clarified the relationship with draft-eckert-anima-stable-
connectivity
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15.5. draft-behringer-anima-autonomic-control-plane-03
o Took out requirement for IPv6 --> that's in the reference doc.
o Added requirement section.
o Changed focus: more focus on autonomic functions, not only virtual
out of band. This goes a bit throughout the document, starting
with a changed abstract and intro.
15.6. draft-ietf-anima-autonomic-control-plane-00
No changes; re-submitted as WG document.
15.7. draft-ietf-anima-autonomic-control-plane-01
o Added some paragraphs in addressing section on "why IPv6 only", to
reflect the discussion on the list.
o Moved the data-plane ACP out of the main document, into an
appendix. The focus is now the virtually separated ACP, since it
has significant advantages, and isn't much harder to do.
o Changed the self-creation algorithm: Part of the initial steps go
into the reference document. This document now assumes an
adjacency table, and domain certificate. How those get onto the
device is outside scope for this document.
o Created a new section 6 "workarounds for non-autonomic nodes", and
put the previous controller section (5.9) into this new section.
Now, section 5 is "autonomic only", and section 6 explains what to
do with non-autonomic stuff. Much cleaner now.
o Added an appendix explaining the choice of RPL as a routing
protocol.
o Formalised the creation process a bit more. Now, we create a
"candidate peer list" from the adjacency table, and form the ACP
with those candidates. Also it explains now better that policy
(Intent) can influence the peer selection. (section 4 and 5)
o Introduce a section for the capability negotiation protocol
(section 7). This needs to be worked out in more detail. This
will likely be based on GRASP.
o Introduce a new parameter: ACP tunnel type. And defines it in the
IANA considerations section. Suggest GRE protected with IPSec
transport mode as the default tunnel type.
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o Updated links, lots of small edits.
15.8. draft-ietf-anima-autonomic-control-plane-02
o Added explicitly text for the ACP channel negotiation.
o Merged draft-behringer-anima-autonomic-addressing-02 into this
document, as suggested by WG chairs.
16. References
[I-D.behringer-anima-autonomic-addressing]
Behringer, M., "An Autonomic IPv6 Addressing Scheme",
draft-behringer-anima-autonomic-addressing-02 (work in
progress), October 2015.
[I-D.behringer-anima-reference-model]
Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L.,
Liu, B., Jeff, J., and J. Strassner, "A Reference Model
for Autonomic Networking", draft-behringer-anima-
reference-model-04 (work in progress), October 2015.
[I-D.behringer-autonomic-control-plane]
Behringer, M., Bjarnason, S., BL, B., and T. Eckert, "An
Autonomic Control Plane", draft-behringer-autonomic-
control-plane-00 (work in progress), June 2014.
[I-D.eckert-anima-stable-connectivity]
Eckert, T. and M. Behringer, "Using Autonomic Control
Plane for Stable Connectivity of Network OAM", draft-
eckert-anima-stable-connectivity-02 (work in progress),
October 2015.
[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., and S.
Bjarnason, "Bootstrapping Key Infrastructures", draft-
ietf-anima-bootstrapping-keyinfra-02 (work in progress),
March 2016.
[I-D.ietf-anima-grasp]
Bormann, C., Carpenter, B., and B. Liu, "A Generic
Autonomic Signaling Protocol (GRASP)", draft-ietf-anima-
grasp-04 (work in progress), March 2016.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<http://www.rfc-editor.org/info/rfc4122>.
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[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>.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
<http://www.rfc-editor.org/info/rfc5082>.
[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>.
[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,
<http://www.rfc-editor.org/info/rfc6550>.
[RFC7404] Behringer, M. and E. Vyncke, "Using Only Link-Local
Addressing inside an IPv6 Network", RFC 7404,
DOI 10.17487/RFC7404, November 2014,
<http://www.rfc-editor.org/info/rfc7404>.
[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>.
[RFC7576] Jiang, S., Carpenter, B., and M. Behringer, "General Gap
Analysis for Autonomic Networking", RFC 7576,
DOI 10.17487/RFC7576, June 2015,
<http://www.rfc-editor.org/info/rfc7576>.
Appendix A. Background on the choice of routing protocol
In a pre-standard implementation, the "IPv6 Routing Protocol for Low-
Power and Lossy Networks (RPL, [RFC6550] was chosen. This
Appendix explains the reasoning behind that decision.
Requirements for routing in the ACP are:
o Self-management: The ACP must build automatically, without human
intervention. Therefore routing protocol must also work
completely automatically. RPL is a simple, self-managing
protocol, which does not require zones or areas; it is also self-
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configuring, since configuration is carried as part of the
protocol (see Section 6.7.6 of [RFC6550]).
o Scale: The ACP builds over an entire domain, which could be a
large enterprise or service provider network. The routing
protocol must therefore support domains of 100,000 nodes or more,
ideally without the need for zoning or separation into areas. RPL
has this scale property. This is based on extensive use of
default routing. RPL also has other scalability improvements,
such as selecting only a subset of peers instead of all possible
ones, and trickle support for information synchronisation.
o Low resource consumption: The ACP supports traditional network
infrastructure, thus runs in addition to traditional protocols.
The ACP, and specifically the routing protocol must have low
resource consumption both in terms of memory and CPU requirements.
Specifically, at edge nodes, where memory and CPU are scarce,
consumption should be minimal. RPL builds a destination-oriented
directed acyclic graph (DODAG), where the main resource
consumption is at the root of the DODAG. The closer to the edge
of the network, the less state needs to be maintained. This
adapts nicely to the typical network design. Also, all changes
below a common parent node are kept below that parent node.
o Support for unstructured address space: In the Autonomic
Networking Infrastructure, node addresses are identifiers, and may
not be assigned in a topological way. Also, nodes may move
topologically, without changing their address. Therefore, the
routing protocol must support completely unstructured address
space. RPL is specifically made for mobile ad-hoc networks, with
no assumptions on topologically aligned addressing.
o Modularity: To keep the initial implementation small, yet allow
later for more complex methods, it is highly desirable that the
routing protocol has a simple base functionality, but can import
new functional modules if needed. RPL has this property with the
concept of "objective function", which is a plugin to modify
routing behaviour.
o Extensibility: Since the Autonomic Networking Infrastructure is a
new concept, it is likely that changes in the way of operation
will happen over time. RPL allows for new objective functions to
be introduced later, which allow changes to the way the routing
protocol creates the DAGs.
o Multi-topology support: It may become necessary in the future to
support more than one DODAG for different purposes, using
different objective functions. RPL allow for the creation of
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several parallel DODAGs, should this be required. This could be
used to create different topologies to reach different roots.
o No need for path optimisation: RPL does not necessarily compute
the optimal path between any two nodes. However, the ACP does not
require this today, since it carries mainly non-delay-sensitive
feedback loops. It is possible that different optimisation
schemes become necessary in the future, but RPL can be expanded
(see point "Extensibility" above).
Appendix B. Alternative: An ACP without Separation
Section 5 explains how the ACP is constructed as a virtually
separated overlay network. An alternative ACP design can be achieved
without the VRFs. In this case, the autonomic virtual addresses are
part of the data plane, and subject to routing, filtering, QoS, etc
on the data plane. The secure tunnels are in this case used by
traffic to and from the autonomic address space. They are still
required to provide the authentication function for all autonomic
packets.
At IETF 93 in Prague, the suggestion was made to not advance with the
data plane ACP, and only continue with the virtually separate ACP.
The reason for this decision is that the contextual separation of the
ACP provides a range of benefits (more robustness, less potential
interactions with user configurations), while it is not much harder
to achieve.
This appendix serves to explain the decision; it will be removed in
the next version of the draft.
Authors' Addresses
Michael H. Behringer (editor)
Cisco Systems
Building D, 45 Allee des Ormes
Mougins 06250
France
Email: mbehring@cisco.com
Steinthor Bjarnason
Cisco Systems
Email: sbjarnas@cisco.com
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Balaji BL
Cisco Systems
Email: blbalaji@cisco.com
Toerless Eckert
Cisco Systems
Email: eckert@cisco.com
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