| ANIMA WG | M. Behringer, Ed. |
| Internet-Draft | |
| Intended status: Standards Track | T. Eckert, Ed. |
| Expires: January 4, 2018 | Huawei |
| S. Bjarnason | |
| Arbor Networks | |
| July 3, 2017 |
An Autonomic Control Plane
draft-ietf-anima-autonomic-control-plane-07
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.
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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.ietf-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 (craft 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 could inadvertently affect control plane connectivity. The Autonomic Control Plane serves several purposes at the same time:
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, and Section 5.6 the first channel types for the ACP.
The document "Autonomic Network 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.
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.
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 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.
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:
The document "Autonomic Network 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.
The Autonomic Control Plane has the following requirements:
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 ACP connectivity over non-autonomic nodes, for example to link autonomic nodes over the general Internet. This is possible, but then has a dependency on routing over the non-autonomic hops.
The Autonomic Control Plane is constructed in the following way (for details, see Section 5):
Note:
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 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.
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.
An autonomic node can be a router, switch, controller, NMS host, or any other IP device. We assume an autonomic node has a globally unique domain certificate (LDevID), as well as an adjacency table.
To establish an ACP securely, an Autnomic Node MUST have a globally unique domain certificate (LDevID), with which it can cryptographically assert its membership in the domain. The document [I-D.ietf-anima-bootstrapping-keyinfra] (BRSKI) describes how a domain certificate can automatically and securely be derived from a vendor specific Unique Device Identifier (UDI) or IDevID certificate.
The domain certificate (LDevID) of an autonomic node MUST contain ANIMA specific information, specifically the domain name, the address of the device in the ACP with the Zone-ID set to zero ("ACP address"). This information MUST be encoded in the LDevID in the subjectAltName / rfc822Name field in the following way:
anima.acp+<ACP address>{+<extensions>}@<domain>
Example:
anima.acp+FDA3:79A6:F6EE:0:200:0:6400:1@example.com
The ACP address MUST be specified in its canonical form, as specified in [RFC5952], to allow for easy textual comparisons.
The optional <extensions> field is used for future extensions to this specification. It MUST be ignored unless otherwise specified.
The subjectAlName / rfc822Name encoding of the ACP domain name and ACP address is used for the following reasons:
In the BRSKI bootstrap process in an ANIMA network, the registrar (acting as an EST server) MUST include the subjectAltName / rfc822Name encoded ACP address and domain name to the enrolling device (called pledge) via its response to the pledges EST CSR Attribute request that is mandatory in BRSKI.
The Certificate Authority in an ANIMA network MUST not change this, and create the respective subjectAltName / rfc822Name in the certificate.
ANIMA nodes can therefore find ACP address and domain using this field in the domain certificate, both for themselves, as well as for other nodes.
See section 4.2.1.6 of [RFC5280] for details on the subjectAltName field.
To know to which nodes to establish an ACP channel, every autonomic node maintains an adjacency table. The adjacency table contains information about adjacent autonomic nodes, at a minimum: node-ID, IP address, domain, certificate. An autonomic device MUST maintain this adjacency table up to date. This table is used to determine to which neighbor an ACP connection is established.
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.
ANrtr1 ------ ANswitch1 --- ANswitch2 ------- ANrtr2
.../ \ \ ...
ANrtrM ------ \ ------- ANrtrN
ANswitchM ...
Figure 2
Consider a large L2 LAN with ANrtr1...ANrtrN connected via some topology of L2 switches (eg: in a large enterprise campus or IoT environment using large L2 LANs). If the discovery protocol used for the ACP is operating at the subnet level, every AN router will see all other AN routers on the LAN as neighbors and a full mesh of ACP channels will be built. If some or all of the AN switches are autonomic with the same discovery protocol, then the full mesh would include those switches as well.
A full mesh of ACP connections like this can creates fundamental challenges. The number of security associations of the secure channel protocols will not scale arbitrarily, especially when they leverage platform accelerated encryption/decryption. Likewise, any other ACP operations needs to scale to the number of direct ACP neigbors. An AN router with just 4 interfaces might be deployed into a LAN with hundreds of neighbors connected via switches. Introducing such a new unpredictable scaling factor requirement makes it harder to support the ACP on arbitrary platforms and in arbitrary deployments.
Predictable scaling requirements for ACP neighbors can most easily be achieved if in topologies like these, AN capable L2 switches can ensure that discovery messages terminate on them so that neighboring AN routers and switches will only find the physcially connected AN L2 switches as their candidate ACP neighbors. With such a discovery mechanism in place, the ACP and its security associations will only need to scale to the number of physcial interfaces instead of a potentially much larger number of "LAN-connected" neighbors. And the ACP topology will follow directly the physical topology, something which can then also be leveraged in management operations or by ASAs.
In the example above, consider ANswitch1 and ANswitchM are AN capable, and ANswitch2 is not AN capable. The desired ACP topology is therefore that ANrtr1 and ANrtrM only have an ACP connetion to ANswitch1, and that ANswitch1, ANrtr2, ANrtrN have a full mesh of ACP connection amongst each other. ANswitch1 also has an ACP connection with ANswitchM and ANswitchM has ACP connections to anything else behind it.
LLDP (and Cisco's CDP) are example of L2 discovery protocols that terminate their messages on L2 ports. If those protocols would be chosen for ACP neighbor discovery, ACP neighbor discovery would therefore also terminate on L2 ports. This would prevent ACP construction over non-ANIMA switches.
mDNS operates at the subnet level, and is also used on L2 switches. The authors of this document are not aware of mDNS implementation that terminate their messages on L2 ports instead of the subnet level. If mDNS was used as the ACP discovery mechanism on an ACP capable L2 switch, then this would be necessary to implement. It is likely that termination of mDNS messages could only be applied to all mDNS messages from a port, which would then make it necessary to software forward any non-ACP related mDNS messages to maintain prior non-ACP mDNS functionality. With low performance of software forwarding in many L2 switches, this could easily make the ACP unsupportable on such L2 switches.
Because of the above considerations, the ACP uses DULL (Discovery Unsolicited Link-Local) insecure instances of GRASP for discovery of ACP neighbors. See section 3.5.2.2 of [I-D.ietf-anima-grasp] These can easily be set up to match the aforementioned requirements without affecting other uses of GRASP. Note that each such DULL instance of GRASP is also used for the discovery of a bootstrap proxy when the device is not yet enrolled into the autonomic domain. Because the discover of ACP neighbors only happens after the device is enrolled into the autonomic domain, it never needs to discover a bootstrap proxy and ACP neighbor at the same time.
An autonomic node announces itself to potential ACP peers by use of the "AN_ACP" objective. This is a synchronization objective intended to be flooded on a single link using the GRASP Flood Synchronization (M_FLOOD) message. In accordance with the design of the Flood message, a locator consisting of a specific link-local IP address, IP protocol number and port number will be distributed with the flooded objective. An example of the message is informally:
[M_FLOOD, 12340815, h'fe80000000000000c0011001FEEF0000, 1,
["AN_ACP", SYNCH-FLAG, 1, "IKEv2"],
[O_IPv6_LOCATOR,
h'fe80000000000000c0011001FEEF0000, UDP, 15000]
]
The formal CDDL definition is:
flood-message = [M_FLOOD, session-id, initiator, ttl,
+[objective, (locator-option / [])]]
objective = ["AN_ACP", objective-flags, loop-count,
objective-value]
objective-flags = ; as in the GRASP specification
loop-count = 1 ; limit to link-local operation
objective-value = text ; name of the (list of) secure
; channel negotiation protocol(s)
The objective-flags field is set to indicate synchronization.
The ttl and loop-count are fixed at 1 since this is a link-local operation.
The session-id is a random number used for loop prevention (distinguishing a message from a prior instance of the same message). In DULL this field is irrelevant but must still be set according to the GRASP specification.
The originator MUST be the IPv6 link local address of the originating autonomic node on the sending interface.
The 'objective-value' parameter is (normally) a string indicating the secure channel protocol available at the specified or implied locator.
The locator is optional and only required when the secure channel protocol is not offered at a well-defined port number, or if there is no well defined port number. For example, "IKEv2" has a well defined port number 500, but in the above example, the candidate ACP neighbor is offering ACP secure channel negotiation via IKEv2 on port 15000 (for the sake of creating the example).
If a locator is included, it MUST be an O_IPv6_LOCATOR, and the IPv6 address MUST be the same as the initiator address (these are DULL requirements to minimize third party DoS attacks).
The secure channel methods defined in this document use the objective values of "IKEv2" and "dTLS". There is no disstinction between IKEv2 native and GRE-IKEv2 because this is purely negotiated via IKEv2.
A node that supports more than one secure channel protocol needs to flood multiple versions of the "AN_ACP" objective, each accompanied by its own locator. This can be in a single GRASP M_FLOOD packet.
If multiple secure channel protocols are supported that all are run on well-defined ports, then they can be announced via a single AN_ACP objective using a list of string names as the objective value without a following locator-option.
Note that a node serving both as an ACP node and BRSKI Join Proxy may choose to distribute the "AN_ACP" objective and "AN_join_proxy" objective in the same flood message, since GRASP allows multiple objectives in one Flood message. This may be impractical though if ACP and BRSKI operations are implemented via separate software modules / ASAs though.
As explained above, in an ACP enabled L2 switch, each of these GRASP instances would actually need to be per-L2-port. The result of the discovery is the IPv6 link-local address of the neighbor as well as its supported secure channel protocols (and non-standard port they are running on). It is stored in the AN Adjacency Table, see Section 5.1.2 which then drives the further building of the ACP to that neighbor.
For example, ANswitch1 would run separate DULL GRASP instances on its ports to ANrtr1, ANswitch2 and ANswitchI, even though all those three ports may be in the data plane in the same (V)LAN. This is easily achieved by extracting native GRASP multicast messages by their MAC multicast destination address. None of the other type of GRASP instances (eg: as used inside the ACP) use GRASP messages that would be affected by such extraction, because all other GRASP messages have encrypted encapsulations.
An autonomic node must determine to which other autonomic nodes in the adjacency table it should build an ACP connection. This is based on the information in the AN Adjacency table.
The ACP is by default established exclusively between nodes in the same domain.
Intent can change this default behaviour. Since Intent is transported over the ACP, the first ACP connection a node establishes is always following the default behaviour. The precise format for this Intent needs to be defined outside this document. Example Intent policies which need to be supported include:
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.
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 seems 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 gateway device may need to support both of these mechanisms and potentially more.
To support extensible secure channel protocol selection without a single common MTI protocol, autonomic devices must try all the ACP secure channel protocols it supports and that are feasible because the candidate ACP neighbor also announced them via its AN_ACP GRASP parameters (these are called the "feasible" ACP secure channel protocols).
To ensure that the selection of the secure channel protocols always succeeds in a predictable fashion without blocking, the following rules apply:
An autonomic device may choose to attempt initiate the different feasible ACP secure channel protocol it supports according to its local policies sequentially or in parallel, but it MUST support acting as a responder to all of them in parallel.
Once the first secure channel protocol succeeds, the two peers know each others certificates (because that must be used by all secure channel protocols for mutual authentication. The device with the lower Device-ID in the ACP address becomes Bob, the one with the higher Device-ID in the certificate Alice.
Bob becomes passive, he does not attempt to further initiate ACP secure channel protocols with Alice and does not consider it to be an error when Alice closes secure channels. Alice becomes the active party, continues to attempt setting up secure channel protocols with Bob until she arrives at the best one (from her view) that also works with Bob.
For example, originally Bob could have been the initiator of one ACP secure channel protocol that Bob preferred and the security association succeeded. The roles of Bob abd Alice are then assigned. At this stage, the protocol may not even have completed negotiationg a common security profile. The protocol could for example have been IPsec. It is not up to Alice to devide how to proceed. Even if the IPsec connecting determined a working profile with Bob, Alice might prefer some other secure protocol (eg: dTLS) and try to set that up with Bob. If that succeeds, she would close the IPsec connection. If no better protocol attempt succeeds, she would keep the IPsec connection.
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. An autonomic device must not assume that neighbors with the same L2 or link-local IPv6 addresses on different L2 interfaces are the ame devices. This can only be determined after examining the certificate after a successful security association attempt.
Independent of the security association protocol choosen, candidate ACP neighbors need to be authenticated based on their autonomic domain certificate. This implies that any security association protocol MUST support certificate based authentication that can support the following verification steps:
This document does not mandate specific support for CRL or OCSP options. If CRL or OCSP URLs are specified in the devices certificate then the device SHOULD connect to the URL via the ACP if it has an IPv6 address that is reachable via the ACP. Better mechanisms to locate CRL or OCSP server(s), for example via GRASP are subject to future documents.
The following sections define the security association protocols that we consider to be important and feasible to specify in this document:
An autonomic device announces its ability to support IKEv2 as the ACP secure channel protcol in GRASP as "IKEv2".
To run ACP via IPsec transport mode, no further IANA assignments/definitions are required. All autonomic devices supporting IPsec MUST support IPsec security setup via IKEv2, transport mode encapsulation via the device and peer link-local IPv6 addresses, AES256 encryption and SHA256 hash.
In terms of IKEv2, this means the initiator will offer to support IPsec transport mode with next protocol equal 41 (IPv6).
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 in the native IPsec case, but instead of directly carrying the ACP IPv6 packets, the payload is an ACP IPv6 packet inside GRE/IPv6. The mandatory security profile is the same as for native IPsec: peer link-local IPv6 addresses, AES256 encryption, SHA256 hash.
In terms of IKEv2 negotiation, this means the initiator must offer to support IPsec transport mode with next protocol equal to GRE (47), followed by 41 (IPv6) (because native IPsec is required to be supported, see below).
If IKEv2 initiator and responder support GRE, it will be selected. The version of GRE to be used must the according to [RFC7676].
We define the use of ACP via dTLS in the assumption that it is likely the first transport encryption code basis supported in some classes of constrained devices.
To run ACP via UDP and dTLS v1.2 [RFC6347] a locally assigned UDP port is used that is announced as a parameter in the GRASP AN_ACP objective to candidate neighbors. All autonomic devices supporting ACP via dTLS must use AES256 encryption.
There is no additional session setup or other security association besides this simple dTLS setup. As soon as the dTLS session is functional, the ACP peers will exchange ACP IPv6 packets as the payload of the dTLS transport connection. Any dTLS defined security association mechanisms such as re-keying are used as they would be for any transport application relying solely on dTLS.
A baseline autonomic device MUST support IPsec. A constrained autonomic device MUST support dTLS. Autonomic edge device connecting constrained areas with baseline areas MUST therefore support IPsec and dTLS.
The MTU for ACP secure channels must be derived locally from the underlying link MTU minus the security encapsulation overhead. Given how ACP channels are built across layer2 connections only, the probability for MTU mismatch is low. For additional reliability, applications to be runa cross the ACP should only assume to have minimum MTU available (1280).
Autonomic devices need to specify in documentation the set of secure ACP mechanisms they suppport.
Received GRASP packets are assigned to an instance of GRASP by the context they are received on:
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, such as a logical container or virtual machine instance. 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.
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 5.8. 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 7 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.
The ACP is based exclusively on IPv6 addressing, for a variety of reasons:
The Base ULA addressing scheme for autonomic nodes has the following format:
8 40 3 77 +--+--------------+------+------------------------------------------+ |FD| hash(domain) | Type | (sub-scheme) | +--+--------------+------+------------------------------------------+
Figure 3: ACP Addressing Base Scheme
The first 48 bits follow the ULA scheme, as defined in [RFC4193], to which a type field is added:
The sub-scheme defined here is defined by the Type value 0 (zero) in the base scheme.
51 13 63 1
+------------------------+---------+----------------------------+---+
| (base scheme) | Zone-ID | Device-ID | V |
+------------------------+---------+----------------------------+---+
Figure 4: ACP Addressing Sub-Scheme
The fields are defined as follows: [Editor's note: The lengths of the fields is for discussion.]
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:
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 = 0 is an identifier, with another zone-ID as a locator. See Section 5.9.4 for a description of the zone bits.
This addressing sub-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.
[EDNOTE: various suggestions from mcr in his mail from 30 Nov 2016 to be considered (https://mailarchive.ietf.org/arch/msg/anima/nZpEphrTqDCBdzsKMpaIn2gsIzI).]
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.
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.
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. Because the domain name in the ACP information field of the certificate is used to authenticate an ACP peers certificate, care must be taken when using such an approach though: To allow for devices in separate subdomains to have mutually permitted certificates, the domain part of the ACP information can not carry the subdomain. Instead it shuold be carried as an extension to the address part. This part will be ignored and instead only the address field using the different subdomain hash based ULA prefix will be used. Example: anima.acp+FDA3:79A6:F6EE:0:200:0:6400:1+sub:subdomainA@example.com
Other ACP addressing sub-schemes can be defined if and when required. IANA would need to assign a new "type" for each new addressing sub-scheme.
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, and this routing runs only inside the ACP.
The routing protocol inside the ACP is RPL ([RFC6550]) with the following profile. See Appendix A for more details on the choice of RPL.
The RPL root can create additional RPL instances with other OF and metrics as desired, eg: via 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 5.10.
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.
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. The ACP is a self-protecting overlay network, which allows by default access only to trusted, autonomic 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. To support connections to adjacent non-autonomic nodes, an autonomic node with ACP must support "ACP connect" (sometimes also connect "autonomic connect"):
"ACP connect" is a function on an autonomic device that we call an "ACP edge device". With "ACP connect", interfaces on the device can be configured to be put into the ACP VRF. The ACP is then accessible to other (NOC) systems on such an interface without those systems having to support any ACP discovery or ACP channel setup. This is also called "native" access to the ACP because to those (NOC) systems the interface looks like a normal network interface (without any encryption/novel-signaling).
data-plane "native" (no ACP)
.
+-----------+ +-----------+ . +-------------+
| | | Autonomic | v | |+
| | | Device |-----------------| |+
| Autonomic |-----------|"ACP edge | | NOC Device ||
| Device | ^ | device" O-----------------| "NMS hosts" ||
| | . | | . ^ | ||
+-----------+ . +-----------+ . . +-------------+|
. . . +-------------+
data-plane "native" . ACP "native" (unencrypted)
+ ACP auto-negotiated .
and encrypted ACP connect interface
eg: "vrf ACP native" (config)
Figure 5: ACP connect
ACP connect has security consequences: All systems and processes connected via ACP connect have access to all autonomic nodes on the entire ACP, without further authentication. Thus, the ACP connect interface and (NOC) systems connected to it must be physically controlled/secured.
The ACP connect interface must be configured with some IPv6 address prefix. This prefix could use the ACP address prefix or could be different. It must be distributed into the ACP routing protocol unless the ACP device is the root of the ACP routing protocol (eg: when all other autonomic devices have a default route in the ACP towards it). The NOC hosts must route the ACP address prefix to the ACP edge devices address on the ACP connect interface.
An ACP connect interface provides exclusively access to only the ACP. This is likely insufficient for many NOC hosts. Instead, they would likely require a second interface outside the ACP for connections between the NMS host and administrators, or Internet based services, or even for direct access to the data plane. The document "Autonomic Network Stable Connectivity" explains in more detail how the ACP can be integrated in a mixed NOC environment.
Note: If an NMS host is autonomic itself, it negotiates access to the ACP with its neighbor, like any other autonomic node and then runs a normal (encrypted) ACP connection to the neighbor.
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.
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.
Future work should envisage an option where the edge device of the L3 cloud is configured to automatically forward ACP discovery messages to the right exit point. This optimisation is not considered in this document.
The ACP is self-healing:
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.
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 5.9).
It is also highly desirable for implementation of the ACP to be able to run it over interfaces that are administratively down. If this is not feasible, then it might instead be possible to request explicit operator override upon administrative actions that would administratively bring down an interface across whicht the ACP is running. Especially if bringing down the ACP is known to disconnect the operator from the device. For example any such down administrative action could perform a dependency check to see if the transport connection across which this action is performed is affected by the down action (with default RPL routing used, packet forwarding will be symmetric, so this is actually possible to check).
As explained in Section 5, the ACP is based on secure channels built between devices that have mutually authenticated each other with 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.
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 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.
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:
There is no prevention of source-address spoofing inside the ACP. This implies that if an attacker gains access to the ACP, (s)he can spoof all addresses inside the ACP and fake messages from any other device.
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.
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, Balaji BL, Alex Clemm, Yves Hertoghs, Bruno Klauser, Max Pritikin, Ravi Kumar Vadapalli.
Special thanks to Pascal Thubert to provide the details for the recommendations of the RPL profile to use in the ACP
Further input and suggestions were received from: Rene Struik, Brian Carpenter, Benoit Claise.
First version of this document: draft-behringer-autonomic-control-plane
Initial version of the anima document; only minor edits.
Addresses (numerous) comments from Brian Carpenter. See mailing list for details. The most important changes are:
No changes; re-submitted as WG document.
Changed discovery of ACP neighbor back from mDNS to GRASP after revisiting the L2 problem. Described problem in discovery section itself to justify. Added text to explain how ACP discovery relates to BRSKY (bootstrap) discovery and pointed to Michael Richardsons draft detailing it. Removed appendix section that contained the original explanations why GRASP would be useful (current text is meant to be better).
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:
The mechanism described in the normative part of this document to support multiple different ACP secure channel protocols without a single network wide MTI protocol is important to allow extending secure ACP channel protocols beyond what is specified in this document, but it will run into problem if it would be used for multiple protocols:
The need to potentially have multiple of these security associations even temporarily run in parallel to determine which of them works best does not support the most lightweight implementation options.
The simple policy of letting one side (Alice) decide what is best may not lead to the mutual best result.
The two limitations can easier be solved if the solution was more modular and as few as possible initial secure channel negotiation protocols would be used, and these protocols would then take on the responsibility to support more flexible objectives to negotiate the mutually preferred ACP security channel protocol.
IKEv2 is the IETF standard protocol to negotiate network security associations. It is meant to be extensible, but it is unclear whether it would be feasible to extend IKEv2 to support possible future requirements for ACP secure channel negotiation:
Consider the simple case where the use of native IPsec vs. IPsec via GRE is to be negotiated and the objective is the maximum throughput. Both sides would indicate some agreed upon performance metric and the preferred encapsulation is the one with the higher performance of the slower side. IKEv2 does not support negotiation with this objective.
Consider dTLS and some form of 802.1AE (MacSEC) are to be added as negotiation options - and the performance objective should work across all IPsec, dDTLS and 802.1AE options. In the case of MacSEC, the negotiation would also need to determine a key for the peering. It is unclear if it would be even appropriate to consider extending the scope of negotiation in IKEv2 to those cases. Even if feasible to define, it is unclear if implementations of IKEv2 would be eager to adopt those type of extension given the long cycles of security testing that necessarily goes along with core security protocols such as IKEv2 implementations.
A more modular alternative to extending IKEv2 could be to layer a modular negotiation mechanism on top of the multitide of existing or possible future secure channel protocols. For this, GRASP over TLS could be considered as a first ACP secure channel negotiation protocol. The following are initial considerations for such an approach. A full specification is subject to a separate document:
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 negotiate the channel mechanism to use using objectives such as performance and perceived quality of the security. After agreeing on a channel mechanism, Alice and Bob start the selected Channel protocol. Once the secure channel protocol is successfully running, the GRASP/TLS connection can be kept alive or timed out as long as the selected channel protocol has a secure association between Alice and Bob. When it terminates, it needs to be re-negotiated via GRASP/TLS.
Notes: