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2 Internet Engineering Task Force E. Haleplidis
3 Internet-Draft University of Patras
4 Intended status: Informational July 08, 2013
5 Expires: January 09, 2014
7 ForCES Model Extension
8 draft-haleplidis-forces-model-extension-04
10 Abstract
12 Forwarding and Control Element Separation (ForCES) defines an
13 architectural framework and associated protocols to standardize
14 information exchange between the control plane and the forwarding
15 plane in a ForCES Network Element (ForCES NE). RFC5812 has defined
16 the ForCES Model provides a formal way to represent the capabilities,
17 state, and configuration of forwarding elements within the context of
18 the ForCES protocol, so that control elements (CEs) can control the
19 FEs accordingly. More specifically, the model describes the logical
20 functions that are present in an FE, what capabilities these
21 functions support, and how these functions are or can be
22 interconnected.
24 RFC5812 has been around for two years and experience in its use has
25 shown room for small extensions without a need to alter the protocol
26 while retaining backward compatibility with older xml libraries.
27 This document extends the model to allow complex datatypes for
28 metadata, optional default values for datatypes and optional access
29 types for structures. The document also introduces three new
30 features, bitmap as a new datatype, a new event condition
31 BecomesEqualTo and LFB properties.
33 Status of This Memo
35 This Internet-Draft is submitted in full conformance with the
36 provisions of BCP 78 and BCP 79.
38 Internet-Drafts are working documents of the Internet Engineering
39 Task Force (IETF). Note that other groups may also distribute
40 working documents as Internet-Drafts. The list of current Internet-
41 Drafts is at http://datatracker.ietf.org/drafts/current/.
43 Internet-Drafts are draft documents valid for a maximum of six months
44 and may be updated, replaced, or obsoleted by other documents at any
45 time. It is inappropriate to use Internet-Drafts as reference
46 material or to cite them other than as "work in progress."
48 This Internet-Draft will expire on January 09, 2014.
50 Copyright Notice
52 Copyright (c) 2013 IETF Trust and the persons identified as the
53 document authors. All rights reserved.
55 This document is subject to BCP 78 and the IETF Trust's Legal
56 Provisions Relating to IETF Documents
57 (http://trustee.ietf.org/license-info) in effect on the date of
58 publication of this document. Please review these documents
59 carefully, as they describe your rights and restrictions with respect
60 to this document. Code Components extracted from this document must
61 include Simplified BSD License text as described in Section 4.e of
62 the Trust Legal Provisions and are provided without warranty as
63 described in the Simplified BSD License.
65 Table of Contents
67 1. Terminology and Conventions . . . . . . . . . . . . . . . . . 2
68 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
69 1.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 2
70 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
71 3. ForCES Model Extension proposal . . . . . . . . . . . . . . . 4
72 3.1. Complex datatypes for Metadata . . . . . . . . . . . . . 4
73 3.2. Optional Default Value for Datatypes . . . . . . . . . . 6
74 3.3. Optional Access Type for Structs . . . . . . . . . . . . 7
75 3.4. New datatype: Bitmap . . . . . . . . . . . . . . . . . . 8
76 3.5. New Event Condition: BecomesEqualTo . . . . . . . . . . . 10
77 3.6. LFB Properties . . . . . . . . . . . . . . . . . . . . . 10
78 3.7. Enhancing XML Validation . . . . . . . . . . . . . . . . 11
79 4. XML Extension Schema for LFB Class Library Documents . . . . 12
80 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
81 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
82 7. Security Considerations . . . . . . . . . . . . . . . . . . . 25
83 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
84 8.1. Normative References . . . . . . . . . . . . . . . . . . 25
85 8.2. Informative References . . . . . . . . . . . . . . . . . 26
86 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 26
88 1. Terminology and Conventions
90 1.1. Requirements Language
92 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
93 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
94 document are to be interpreted as described in [RFC2119].
96 1.2. Definitions
97 This document follows the terminology defined by the ForCES Model in
98 [RFC5812]. The required definitions are repeated below for clarity.
100 FE Model - The FE model is designed to model the logical
101 processing functions of an FE. The FE model proposed in this
102 document includes three components; the LFB modeling of individual
103 Logical Functional Block (LFB model), the logical interconnection
104 between LFBs (LFB topology), and the FE-level attributes,
105 including FE capabilities. The FE model provides the basis to
106 define the information elements exchanged between the CE and the
107 FE in the ForCES protocol [RFC5810].
109 LFB (Logical Functional Block) Class (or type) - A template that
110 represents a fine-grained, logically separable aspect of FE
111 processing. Most LFBs relate to packet processing in the data
112 path. LFB classes are the basic building blocks of the FE model.
114 LFB Instance - As a packet flows through an FE along a data path,
115 it flows through one or multiple LFB instances, where each LFB is
116 an instance of a specific LFB class. Multiple instances of the
117 same LFB class can be present in an FE's data path. Note that we
118 often refer to LFBs without distinguishing between an LFB class
119 and LFB instance when we believe the implied reference is obvious
120 for the given context.
122 LFB Model - The LFB model describes the content and structures in
123 an LFB, plus the associated data definition. XML is used to
124 provide a formal definition of the necessary structures for the
125 modeling. Four types of information are defined in the LFB model.
126 The core part of the LFB model is the LFB class definitions; the
127 other three types of information define constructs associated with
128 and used by the class definition. These are reusable data types,
129 supported frame (packet) formats, and metadata.
131 Element - Element is generally used in this document in accordance
132 with the XML usage of the term. It refers to an XML tagged part
133 of an XML document. For a precise definition, please see the full
134 set of XML specifications from the W3C. This term is included in
135 this list for completeness because the ForCES formal model uses
136 XML.
138 Attribute - Attribute is used in the ForCES formal modeling in
139 accordance with standard XML usage of the term, i.e., to provide
140 attribute information included in an XML tag.
142 LFB Metadata - Metadata is used to communicate per-packet state
143 from one LFB to another, but is not sent across the network. The
144 FE model defines how such metadata is identified, produced, and
145 consumed by the LFBs, but not how the per-packet state is
146 implemented within actual hardware. Metadata is sent between the
147 FE and the CE on redirect packets.
149 ForCES Component - A ForCES Component is a well-defined, uniquely
150 identifiable and addressable ForCES model building block. A
151 component has a 32-bit ID, name, type, and an optional synopsis
152 description. These are often referred to simply as components.
153 LFB Component - An LFB component is a ForCES component that
154 defines the Operational parameters of the LFBs that must be
155 visible to the CEs.
157 LFB Class Library - The LFB class library is a set of LFB classes
158 that has been identified as the most common functions found in
159 most FEs and hence should be defined first by the ForCES Working
160 Group.
162 2. Introduction
164 The ForCES Model [RFC5812] presents a formal way to define FEs
165 Logical Function Blocks (LFBs) using XML. [RFC5812] has been
166 published a more than two years and current experience in its use has
167 demonstrated need for adding new and changing existing modeling
168 concepts.
170 Specifically this document extends the ForCES Model to allow complex
171 datatypes for metadata, optional default values for datatypes and
172 optional access types for structures. Additionally the document
173 introduces three new features, bitmap as a new datatype, a new event
174 condition BecomesEqualTo and LFB properties.
176 These extensions are an addendum to the ForCES model [RFC5812] and do
177 not require any changes on the ForCES protocol [RFC5810] as they are
178 simply changes of the schema definition. Additionally backward
179 compatibility is ensured as xml libraries produced with the earlier
180 schema are still valid with the new one.
182 XXX: Discussion is needed to specify whether bitmap required protocol
183 definition of how bitmap is sent through the wire.
185 3. ForCES Model Extension proposal
187 3.1. Complex datatypes for Metadata
189 Section 4.6. (Element for Metadata Definitions) in the ForCES Model
190 [RFC5812] limits the datatype use in metadata to only atomic types.
191 Figure 1 shows the xml schema excerpt where ony typeRef and atomic
192 are allowed for a metadata definition.
194 However there are cases where complex metadata are used in the
195 datapath, for example two simple use cases can be seen in the
196 OpenFlow switch 1.1 [OpenFlowSpec1.1] and beyond:
198 1. The Action Set metadata follows a packet inside the Flow Tables.
199 The Action Set metadata is an array of actions to be performed at
200 the end of the pipeline.
202 2. When a packet is received from a controller it may be accompanied
203 by a list of actions to be performed on it prior to be sent on
204 the flow table pipeline which is also an array.
206 With this extension (Figure 2), complex data types are also allowed,
207 specifically structs and arrays as metadata. The key declarations
208 are required to check for validity of content keys in arrays and
209 componentIDs in structs.
211
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230 Figure 1: Initial MetadataDefType Defintion in the schema
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263 Figure 2: New MetadataDefType Defintion for the schema
265 3.2. Optional Default Value for Datatypes
267 In the original schema, default values can only be defined for
268 datatypes defined inside LFB components and not inside structures or
269 arrays. Therefore default values of datatypes that are constantly
270 being reused, e.g. counters with default value of 0, have to be
271 constantly respecified. Additionally, datatypes inside complex
272 datatypes cannot be defined with a default value, e.g. a counter
273 inside a struct that has a default value of 0.
275 This extension allows optionally to add default values to atomic and
276 typeref types, whether they are as simple or complex datatypes. A
277 simple use case would be to have a struct component where one of the
278 components is a counter which the default value would be zero.
280 This extension alters the definition of the typeDeclarationGroup in
281 the xml schema from Figure 3 to Figure 4 to allow default values to
282 TypeRef.
284
286 Figure 3: Initial Excerpt of typeDeclarationGroup Defintion in the
287 schema
289
290
291
293
295 Figure 4: New Excerpt of typeDeclarationGroup Defintion in the schema
297 Additionally it appends to the declaration of the AtomicType this xml
298 (Figure 5) to allow default values to Atomic datatypes.
300
302 Figure 5: Appending xml in of AtomicType Defintion in the schema
304 3.3. Optional Access Type for Structs
306 In the original schema, the access type can be only be defined on
307 components of LFB and not on components in structs or arrays.
308 However when it's a struct datatype it is not possible to fine-tune
309 access type per component in the struct. A simple use case would be
310 to have a read-write struct component where one of the components is
311 a counter where the access-type could be read-reset or read-only,
312 e.g. a read-reset or a read-only counter inside a struct.
314 With this extension is it allowed to define the access type for a
315 struct component either in the datatype definitions or in the LFB
316 component definitions.
318 When the optional access type for a struct component is defined it
319 MUST override the access type of the struct. If by accident an
320 access type for a component in a capability is defined, the access
321 type MUST NOT be taken into account and MUST always be considered as
322 read-only.
324 This extension alters the definition of the struct in the xml schema
325 from Figure 6 to Figure 7.
327
328
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347 Figure 6: Initial xml for the struct definition in the schema
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375 Figure 7: New xml for the struct definition in the schema
377 3.4. New datatype: Bitmap
379 With the current schema it is valid to create a struct of booleans in
380 order to simulate a bitmap value. However each boolean is sent as
381 4bytes. This extension adds the bitmap, a set of sequential named
382 bits.
384 Bitmaps may be useful in describing capabilities, e.g. Link speed
385 capabilities as multiple boolean values.
387 XXX Discussion may be required as to whether there is a need for
388 protocol description of how the bitmap is sent through the wire.
390 In the new schema, bits are named followed an optional bit value. An
391 example:
393
394 Bitmap example
395 A bitmap field example
396
397
398
399
400
402 Figure 8: Example of bitmap Defintion
404 The ordering of the bits MUST be implemented in the order that are
405 defined in the xml library.
407 The bitmap is defined in the model extension schema is as follows:
409
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427 Figure 9: New Excerpt of bitmap Defintion in the schema
429 Along with the needed addition to the typeDeclarationGroup
430 Definition:
432
434 Figure 10: New Excerpt of typeDeclarationGroup Defintion in the
435 schema
437 3.5. New Event Condition: BecomesEqualTo
439 This extensions adds one more event condition in the model schema,
440 that of BecomesEqualTo. The difference between Greater Than and Less
441 Than, is that when the value is exactly that of the BecomesEqualTo,
442 the event is triggered. This event condition is particular useful
443 when there is a need to monitor one or more states of an LFB or the
444 FE. For example in the CEHA [I-D.ietf-forces-ceha] document it may
445 be useful for the master CE to know which backup CEs have just become
446 associated in order to connect to them and begin synchronizing the
447 state of the FE. The master CE could always poll for such
448 information but getting such an event will speed up the process and
449 the event may be useful in other cases as well for monitoring state.
451 The event MUST be triggered only when the value of the targeted
452 component becomes equal to the event condition value and MUST NOT
453 generate events while the targeted component's value remains equal to
454 the event condition's value.
456 The BecomesEqualTo is appended to the schema as follows:
458
461 Figure 11: New Excerpt of BecomesEqualTo event condition definition
462 in the schema
464 3.6. LFB Properties
466 The current model definition specifies properties for components of
467 LFBs. Experience however has proven valuable at least for debug
468 reasons, to have statistics per LFB instance to monitor sent/received
469 messages and errors for communication between CE and FE. These
470 properties are read-only.
472 XXX: Discussion for addressing LFB properties. Possibly in the
473 protocol extension?
475 The following datatype definitions are to be used as properties for
476 LFB instances.
478
479 LFBProperties
480 LFB Properties definition
481
482
483 SentToCE
484 Messages sent to CE
485 uint32
486
487
488 SentErrorsToCE
489 Error messages sent to CE
490 uint32
491
492
493 ReceivedFromCE
494 Messages received from CE
495 uint32
496
497
498 ReceivedErrorsFromCE
499 Error messages received from CE
500 uint32
501
502
503
505 Properties for LFB instances
507 3.7. Enhancing XML Validation
509 As specified earlier this is not an extension but an enhancement of
510 the schema to provide additional validation rules. This includes
511 adding new key declarations to provide uniqueness as deinfed by the
512 ForCES Model [RFC5812]. Such validations work only on within the
513 same xml file.
515 The following validation rules have been appended in the original
516 schema in [RFC5812]:
518 1. Each metadata ID must be unique.
520 2. LFB Class IDs must be unique.
522 3. Component ID, Capability ID and Event Base ID must be unique per
523 LFB.
525 4. Event IDs must be unique per LFB.
527 5. Special Values in Atomic datatypes must be unique per atomic
528 datatype.
530 4. XML Extension Schema for LFB Class Library Documents
532
533
538
539
540 Schema for Defining LFB Classes and associated types (
541 frames, data types for LFB attributes, and metadata).
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1176 OpenFlow XML Library
1178 5. Acknowledgements
1180 The author would like to acknowledge Joel Halpern, Jamal Hadi and
1181 Dave Hood for their comments and discussion that helped shape this
1182 document in a better way.
1184 6. IANA Considerations
1186 This memo includes no request to IANA.
1188 7. Security Considerations
1190 The security considerations that have been described in the ForCES
1191 Model RFC [RFC5812] apply to this document as well.
1193 8. References
1195 8.1. Normative References
1197 [I-D.ietf-forces-ceha]
1198 Ogawa, K., Wang, W., Haleplidis, E., and J. Salim, "ForCES
1199 Intra-NE High Availability", draft-ietf-forces-ceha-07
1200 (work in progress), May 2013.
1202 [OpenFlowSpec1.1]
1203 http://www.OpenFlow.org/, "The OpenFlow 1.1
1204 Specification.", , .
1207 [RFC5810] Doria, A., Hadi Salim, J., Haas, R., Khosravi, H., Wang,
1208 W., Dong, L., Gopal, R., and J. Halpern, "Forwarding and
1209 Control Element Separation (ForCES) Protocol
1210 Specification", RFC 5810, March 2010.
1212 [RFC5812] Halpern, J. and J. Hadi Salim, "Forwarding and Control
1213 Element Separation (ForCES) Forwarding Element Model", RFC
1214 5812, March 2010.
1216 8.2. Informative References
1218 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
1219 Requirement Levels", BCP 14, RFC 2119, March 1997.
1221 Author's Address
1223 Evangelos Haleplidis
1224 University of Patras
1225 Department of Electrical and Computer Engineering
1226 Patras 26500
1227 Greece
1229 Email: ehalep@ece.upatras.gr