Internet Engineering Task Force E. Haleplidis
Internet-Draft University of Patras
Updates: 5812 (if approved) July 4, 2014
Intended status: Standards Track
Expires: January 5, 2015
ForCES Model Extension
draft-ietf-forces-model-extension-03
Abstract
Forwarding and Control Element Separation (ForCES) defines an
architectural framework and associated protocols to standardize
information exchange between the control plane and the forwarding
plane in a ForCES Network Element (ForCES NE). RFC5812 has defined
the ForCES Model that provides a formal way to represent the
capabilities, state, and configuration of forwarding elements within
the context of the ForCES protocol, so that control elements (CEs)
can control the FEs accordingly. More specifically, the model
describes the logical functions that are present in a forwarding
element (FE), what capabilities these functions support, and how
these functions are or can be interconnected.
RFC5812 has been around for two years and experience in its use has
shown room for small extensions without a need to alter the protocol
while retaining backward compatibility with older xml libraries.
This document update RFC5812 and extends the model to allow complex
datatypes for metadata, optional default values for datatypes,
optional access types for structures and fixes an issue with LFB
inheritance. The document also introduces two new features a new
event condition BecomesEqualTo and LFB properties.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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Copyright Notice
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document authors. All rights reserved.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
2. ForCES Model Extensions . . . . . . . . . . . . . . . . . . . 4
2.1. Complex datatypes for Metadata . . . . . . . . . . . . . 4
2.2. Optional Default Value for Datatypes . . . . . . . . . . 5
2.3. Optional Access Type for Structs . . . . . . . . . . . . 8
2.4. New Event Condition: BecomesEqualTo . . . . . . . . . . . 10
2.5. LFB Properties . . . . . . . . . . . . . . . . . . . . . 11
2.6. LFB class inheritance . . . . . . . . . . . . . . . . . . 13
2.7. Enhancing XML Validation . . . . . . . . . . . . . . . . 14
3. XML Extension Schema for LFB Class Library Documents . . . . 14
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
6. Security Considerations . . . . . . . . . . . . . . . . . . . 28
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
7.1. Normative References . . . . . . . . . . . . . . . . . . 28
7.2. Informative References . . . . . . . . . . . . . . . . . 29
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
The ForCES Model [RFC5812] presents a formal way to define FEs
Logical Function Blocks (LFBs) using the eXtensible Markup Language
(XML). [RFC5812] has been published a more than two years and
current experience in its use has demonstrated need for adding new
and changing existing modeling concepts.
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Specifically this document updates the ForCES Model [RFC5812] to
allow complex datatypes for metadata (Section 2.1), optional default
values for datatypes (Section 2.2), optional access types for
structures (Section 2.3) and fixes an issue with LFB class
inheritance (Section 2.6). Additionally the document introduces two
new features a new event condition BecomesEqualTo (Section 2.4) and
LFB properties (Section 2.5).
These extensions are an update to the ForCES model [RFC5812] and do
not require any changes on the ForCES protocol [RFC5810] as they are
simply changes of the schema definition. Additionally backward
compatibility is ensured as XML libraries produced with the earlier
schema are still valid with the new one. In order for XML libraries
produced by the new schema to be compatible with existing ForCES
implementations, the XML Libraries MUST NOT include any of the
features described in this document, else the old implementation will
be unable to parse the XML library.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.2. Definitions
This document uses the terminology defined in the ForCES Model in
[RFC5812]. In particular, the reader is expected to be familiar with
the following terms:
FE Model
LFB (Logical Functional Block) Class (or type)
LFB Instance
LFB Model
Element
Attribute
LFB Metadata
ForCES Component
LFB Class Library
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2. ForCES Model Extensions
2.1. Complex datatypes for Metadata
Section 4.6. (Element for Metadata Definitions) in the ForCES Model
[RFC5812] limits the datatype use in metadata to only atomic types.
Figure 1 shows the xml schema excerpt where ony typeRef and atomic
are allowed for a metadata definition.
However there are cases where complex metadata are used in the
datapath, for example two simple use cases can be seen in the
OpenFlow switch 1.1 [OpenFlowSpec1.1] and beyond:
1. The Action Set metadata is an array of actions descriptors, which
traverses the processing pipeline along with the packet data.
2. When a packet is received from a controller it may be accompanied
by a list of actions, as metadata, to be performed on it prior to
being sent on the processing pipeline. This list of actions is
also an array.
With this extension (Figure 2), complex data types are also allowed,
specifically structs and arrays as metadata. The key declarations
are required to check for validity of content keys in arrays and
componentIDs in structs.
Figure 1: Initial MetadataDefType Definition in the schema
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Figure 2: New MetadataDefType Definition for the schema
2.2. Optional Default Value for Datatypes
In the original schema, default values can only be defined for
datatypes defined inside LFB components and not inside structures or
arrays. Therefore default values of datatypes that are constantly
being reused, e.g. counters with default value of 0, have to be
constantly respecified. Additionally, datatypes inside complex
datatypes cannot be defined with a default value, e.g. a counter
inside a struct that has a default value of 0.
This extension allows optionally to add default values to atomic and
typeref types, whether they are as simple or complex datatypes. A
simple use case would be to have a struct component where one of the
components is a counter which the default value would be zero.
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This extension alters the definition of the typeDeclarationGroup in
the XML schema from Figure 3 to Figure 4 to allow default values to
TypeRef.
Figure 3: Initial Excerpt of typeDeclarationGroup Defintion in the
schema
Figure 4: New Excerpt of typeDeclarationGroup Definition in the
schema
Additionally this document appends to the declaration of the
AtomicType from Figure 5 to Figure 6 to allow default values to
Atomic datatypes. Note that both declarations include the new
special value validation described in Section 2.7
Figure 5: Initial Excerpt of AtomicType Definition in the schema
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Figure 6: New Excerpt of AtomicType Definition in the schema
Examples of using default values is depicted in Figure 7.
Counter Values
Example default values in struct
GoodPacketCoutner
A counter for good packets
uint32
0
BadPacketCoutner
A counter for bad packets
uint32
0
Figure 7: Example of optional default values
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2.3. Optional Access Type for Structs
In the original schema, the access type can only be defined on
components of an LFB and not on components in structs or arrays.
However when it's a struct datatype it is not possible to fine-tune
access type per component in the struct. A simple use case would be
to have a read-write struct component where one of the components is
a counter where the access-type could be read-reset or read-only,
e.g. a read-reset or a read-only counter inside a struct.
With this extension is it allowed to define the access type for a
struct component either in the datatype definitions or in the LFB
component definitions.
When the optional access type for a struct component is defined it
MUST override the access type of the struct. The access type for a
component in a capability is always read-only per [RFC5812]. If an
access type is provided for a component in a capability it MUST be
ignored. Similarly if an access type is provided for a struct in a
metadata it MUST be ignored.
This extension alters the definition of the struct in the xml schema
from Figure 8 to Figure 9.
Figure 8: Initial xml for the struct definition in the schema
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Figure 9: New xml for the struct definition in the schema
An example of using optional access types for structs can be depicted
in Figure 10
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PacketFlows
Packet Flows, match and counter
FlowMatch
Flow Match
MatchType
MatchCounter
Packets matching the flow match
uint32
0
Figure 10: Example of optional access types for struct
2.4. New Event Condition: BecomesEqualTo
This extensions adds one more event condition in the model schema,
that of BecomesEqualTo. The difference between Greater Than and Less
Than, is that when the value is exactly that of the BecomesEqualTo,
the event is triggered. This event condition is particularly useful
when there is a need to monitor one or more states of an LFB or the
FE. For example in the CE High Availability (CEHA) [RFC7121] RFC it
may be useful for the master CE to know which backup CEs have just
become associated in order to connect to them and begin synchronizing
the state of the FE. The master CE could always poll for such
information but getting such an event will speed up the process and
the event may be useful in other cases as well for monitoring state.
The event MUST be triggered only when the value of the targeted
component becomes equal to the event condition value and MUST NOT
generate events while the targeted component's value remains equal to
the event condition's value.
The BecomesEqualTo is appended to the schema as follows:
Figure 11: New Excerpt of BecomesEqualTo event condition definition
in the schema
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It can become useful for the CE to be notified when the state has
changed once the BecomesEqualTo event has been triggered, e.g. the CE
may need to know when a backup CE has lost association. Such an
event can be generated either by defining a second event on the same
component, namely an Event Changed, or by simply reusing
BecomesEqualTo and use event properties, in particular event
hysteresis. We append the following definition for the event
hysteresis defined in section 4.8.5.2 in [RFC5812], with V being the
hysteresis value:
o For an condition, after the last
notification a new notification MUST be
generated only one time once the value has changed by +/- V.
For example using the value of 1 for V, will in effect create a
singular event that will notify the CE that the value has changed by
at least 1.
A developer of a CE must also take into account to use count or time
filtering to avoid being overrun by messages, e.g. in the case of
rapid state changes.
2.5. LFB Properties
The current model definition specifies properties for components of
LFBs. Experience has shown that, at least for debug reasons, it
would be useful to have statistics per LFB instance to monitor sent/
received messages and errors in communication between CE and FE.
These properties are read-only.
In order to avoid ambiguity on protocol path semantics, this document
defines that the LFB component with ID 0 specifically MUST target LFB
properties and ID 0 MUST NOT be used for any component definition.
This disallowment is backwards compatible as no known LFB definition
uses LFB component with ID 0. Any command with a path starting from
LFB component 0 refers to LFB properties. The following change in
the xml schema disallows usage of LFB component 0:
Figure 12: Initial xml for LFB Component IDs
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Figure 13: New xml for the disallowing usage of 0 as LFB Component
The following datatype definitions are to be used as properties for
LFB instances.
LFBProperties
LFB Properties definition
PacketsSentToCE
Packets sent to CE
uint32
SentErrorPacketsToCE
Error Packets sent to CE
uint32
BytesSentToCE
Bytes sent to CE
uint32
SentErrorBytesToCE
Error Bytes sent to CE
uint32
PacketsReceivedFromCE
Packets received from CE
uint32
ReceivedErrorPacketsFromCE
Error Packets received from CE
uint32
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BytesReceivedFromCE
Bytesreceived from CE
uint32
ReceivedErrorBytesFromCE
Error Bytes received from CE
uint32
Properties for LFB instances
2.6. LFB class inheritance
The ForCES model [RFC5812] allows inheritance for LFB classes.
However the xml schema defines only the LFB class from which an LFB
class may inherit. Recent implementations have identified an issue
where ambiguity rises when different versions of an LFB class exists.
This document augments the derivedFrom part of the LFB class
definition with an optional version attribute when the derivedFrom
field is used.
Having the version attribute as optional was a decision based on the
need to maintain backwards compatibility with the XML schema defined
in [RFC5812]. However if the version is omitted, then in the
presence of multiple versions of the same LFB class, the derivedFrom
will always select the latest version.
This extension alters the definition of the derivedFrom in the xml
schema from Figure 14 to Figure 15.
Figure 14: Initial xml for the LFB class inheritance
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Figure 15: New xml for the LFB class inheritance
An example of the use of the version attribute is given in Figure 16
EtherPHYCop
Figure 16: Example of use of new xml for LFB class Inheritance
2.7. Enhancing XML Validation
As specified earlier this is not an extension but an enhancement of
the schema to provide additional validation rules. This includes
adding new key declarations to provide uniqueness as defined by the
ForCES Model [RFC5812]. Such validations work only on within the
same xml file.
The following validation rules have been introduced that did not
exist in the original schema in [RFC5812]:
1. Each metadata ID must be unique.
2. LFB Class IDs must be unique.
3. Component ID, Capability ID and Event Base ID must be unique per
LFB.
4. Event IDs must be unique per LFB.
5. Special Values in Atomic datatypes must be unique per atomic
datatype.
3. XML Extension Schema for LFB Class Library Documents
This section includes the new XML Schema. Note that the namespace
number has been updated from 1.0 to 1.1
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Schema for Defining LFB Classes and associated types
(frames, data types for LFB attributes, and metadata).
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ForCES LFB XML Schema
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4. Acknowledgements
The author would like to acknowledge Joel Halpern, Jamal Hadi Salim
and Dave Hood for their comments and discussion that helped shape
this document in a better way.
5. IANA Considerations
IANA has registered a new XML namespace, as per the guidelines in RFC
3688 [RFC3688].
URI: The URI for this namespace is
urn:ietf:params:xml:ns:forces:lfbmodel:1.1
Registrant Contact: IESG
XML: none, this is an XML namespace
6. Security Considerations
The changes described in this document have no effect on security as
they are simply constructs to write XML library definitions. Thus
they have no effect on security semantics with the protocol and as
such the security considerations that have been described in the
ForCES Model RFC [RFC5812] apply to this document as well.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC5810] Doria, A., Hadi Salim, J., Haas, R., Khosravi, H., Wang,
W., Dong, L., Gopal, R., and J. Halpern, "Forwarding and
Control Element Separation (ForCES) Protocol
Specification", RFC 5810, March 2010.
[RFC5812] Halpern, J. and J. Hadi Salim, "Forwarding and Control
Element Separation (ForCES) Forwarding Element Model", RFC
5812, March 2010.
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[RFC7121] Ogawa, K., Wang, W., Haleplidis, E., and J. Hadi Salim,
"High Availability within a Forwarding and Control Element
Separation (ForCES) Network Element", RFC 7121, February
2014.
7.2. Informative References
[OpenFlowSpec1.1]
http://www.OpenFlow.org/, "The OpenFlow 1.1
Specification.", .
Author's Address
Evangelos Haleplidis
University of Patras
Department of Electrical and Computer Engineering
Patras 26500
Greece
Email: ehalep@ece.upatras.gr
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