Internet Engineering Task Force J. Hadi Salim
Internet-Draft Mojatatu Networks
Intended status: Informational July 05, 2013
Expires: January 06, 2014
ForCES Protocol Extensions
draft-jhs-forces-protoextenstion-01
Abstract
Experience in implementing and deploying ForCES architecture has
demonstrated need for a few small extensions both to ease
programmability and to improve wire efficiency of some transactions.
This document describes a few extensions to the ForCES Protocol
Specification [RFC5810] semantics to achieve that end goal.
Status of This Memo
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Table of Contents
1. Terminology and Conventions . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
1.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Problem Overview . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Table Ranges . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Table Append . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Error codes . . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Bitmap Datatype . . . . . . . . . . . . . . . . . . . . . 6
4. Protocol Update Proposal . . . . . . . . . . . . . . . . . . 6
4.1. Table Ranges . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Table Append . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Error Codes . . . . . . . . . . . . . . . . . . . . . . . 8
4.4. Bitmap Datatype . . . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Terminology and Conventions
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 reiterates the terminology defined by the ForCES
architecture in various documents for the sake of clarity.
FE Model - The FE model is designed to model the logical
processing functions of an FE. The FE model proposed in this
document includes three components; the LFB modeling of individual
Logical Functional Block (LFB model), the logical interconnection
between LFBs (LFB topology), and the FE-level attributes,
including FE capabilities. The FE model provides the basis to
define the information elements exchanged between the CE and the
FE in the ForCES protocol [RFC5810].
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LFB (Logical Functional Block) Class (or type) - A template that
represents a fine-grained, logically separable aspect of FE
processing. Most LFBs relate to packet processing in the data
path. LFB classes are the basic building blocks of the FE model.
LFB Instance - As a packet flows through an FE along a data path,
it flows through one or multiple LFB instances, where each LFB is
an instance of a specific LFB class. Multiple instances of the
same LFB class can be present in an FE's data path. Note that we
often refer to LFBs without distinguishing between an LFB class
and LFB instance when we believe the implied reference is obvious
for the given context.
LFB Model - The LFB model describes the content and structures in
an LFB, plus the associated data definition. XML is used to
provide a formal definition of the necessary structures for the
modeling. Four types of information are defined in the LFB model.
The core part of the LFB model is the LFB class definitions; the
other three types of information define constructs associated with
and used by the class definition. These are reusable data types,
supported frame (packet) formats, and metadata.
LFB Metadata - Metadata is used to communicate per-packet state
from one LFB to another, but is not sent across the network. The
FE model defines how such metadata is identified, produced, and
consumed by the LFBs, but not how the per-packet state is
implemented within actual hardware. Metadata is sent between the
FE and the CE on redirect packets.
ForCES Component - A ForCES Component is a well-defined, uniquely
identifiable and addressable ForCES model building block. A
component has a 32-bit ID, name, type, and an optional synopsis
description. These are often referred to simply as components.
LFB Component - An LFB component is a ForCES component that
defines the Operational parameters of the LFBs that must be
visible to the CEs.
ForCES Protocol - Protocol that runs in the Fp reference points in
the ForCES Framework [RFC3746].
ForCES Protocol Layer (ForCES PL) - A layer in the ForCES protocol
architecture that defines the ForCES protocol messages, the
protocol state transfer scheme, and the ForCES protocol
architecture itself as defined in the ForCES Protocol
Specification [RFC5810].
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ForCES Protocol Transport Mapping Layer (ForCES TML) - A layer in
ForCES protocol architecture that uses the capabilities of
existing transport protocols to specifically address protocol
message transportation issues, such as how the protocol messages
are mapped to different transport media (like TCP, IP, ATM,
Ethernet, etc.), and how to achieve and implement reliability,
ordering, etc. the ForCES SCTP TML [RFC5811] describes a TML that
is mandated for ForCES.
2. Introduction
Experience in implementing and deploying ForCES architecture has
demonstrated need for a few small extensions both to ease
programmability and to improve wire efficiency of some transactions.
This document describes a few extensions to the ForCES Protocol
Specification [RFC5810] semantics to achieve that end goal.
This document describes and justifies the need for 4 small extensions
which are backward compatible.
1. A table range operation to allow a controller or control
application to request or delete an arbitrary range of table
rows.
2. A table append operation to allow a controller to add a new table
row using the next available table index.
3. Improved Error codes returned to the controller (or control
application) to improve granularity of existing defined error
codes.
4. Optimization to packing and addressing commonly used bitmap
structure.
3. Problem Overview
In this section we present sample use cases to illustrate the
challenge being addressed.
3.1. Table Ranges
Consider, for the sake of illustration, an FE table with 1 million
reasonably sized table rows which are sparsely populated.
ForCES GET requests sent from a controller (or control app) are
prepended with a path to a component and sent to the FE. In the case
of indexed tables, the component path can either be to a table or a
table row index. A control application attempting to retrieve the
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first 2000 table rows appearing between row indices 23 and 10023 can
achieve its goal in one of:
o Dump the whole table and filter for the needed 2000 table rows.
o Send upto 10000 ForCES PL requests with monotonically incrementing
indices and stop when the needed 2000 entries are retrieved.
o Use ForCES batching to send fewer large messages (several path
requests at a time with incrementing indices until you hit the
require number of entries).
All of these approaches are programmatically (from an application
point of view) unfriendly, tedious, and are seen as abuse of both
compute and bandwidth resources.
3.2. Table Append
For the sake of illustration, assume that a newly spawned controller
application wishes to install a table row but it has no apriori
knowledge of which table index to use.
ForCES allows a controller/control app to request for the next
available table index as demonstrated in (Figure 1) (refer to
[RFC5810] section 4.8.2 for details of table properties).
CE/App FE
| |
| |
|GETproperty firstUnusedSubscript of table X |
1 |------------------------------------------->|
| |
| Table X firstUnusedSubscript is 1234 |
2 |<-------------------------------------------|
| |
| Table update using index 1234 |
3 |<------------------------------------------>|
| |
Figure 1: ForCES table property request
The problem with the above setup is the application requires one
roundtrip time to figure out the index to insert into. Moreover,
depending on implementation (and in presence of multiple control
applications):
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1. there is no guarantee that the next available subscript in the
above example would stay at 1234 at the moment an application
chooses to do the update; this will entirely depend on
implementation at the FE and/or available holes in the table.
2. In case of multiple apps wishing to insert rows to the same table
concurently, all contending apps will be returned the same value
for unused subscript; however, if all the contending apps try to
insert at the same time, only the first one to reach the FE row
will succeed. A solution involving a reservation mechanism to
ask for an index will contribute complexity.
We conclude that even in the best case scenario, if the application
wishes to insert more than one entry, it will have to incur the
roundtrip time for every to-be-inserted table row. This greatly
affects table add latencies and update rates.
3.3. Error codes
[RFC5810] has defined a generic set of error codes that are to be
returned to the CE from an FE. Deployment experience has shown that
it would be useful to have more fine grained error codes. As an
example, the error code E_NOT_SUPPORTED could be mapped to many FE
error source possibilities that need to be then interpreted by the
caller based on some understanding of the nature of the sent request.
This makes debugging more time consuming.
3.4. Bitmap Datatype
TBA
4. Protocol Update Proposal
This section describes proposals to update the protocol for issues
discussed in Section 3
4.1. Table Ranges
We propose to add a Table-range TLV (type ID 0x117) that will be
associated with the PATH-DATA TLV in the same manner the KEYINFO-TLV
is.
OPER = GET
PATH-DATA:
flags = F_SELTABRANGE, IDCount = 2, IDs = {1,6}
TABLERANGE-TLV = {11,23}
Figure 2: ForCES table range request
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Figure 2 illustrates a GET request for a a table range for rows 11 to
23 of a table with component path of 1/6.
Path flag of F_SELTABRANGE (0x2 i.e bit 1, where bit 0 is F_SELKEY as
defined in RFC 5810) is set to indicate the presence of the Table-
range TLV. The pathflag bit F_SELTABRANGE can only be used in a GET
and is mutually exclusive with F_SELKEY. The FE MUST enforce those
constraints and reject a request with an error code of
E_INVALID_FLAGS with an english description of what the problem is
(refer to Section 4.3).
The Table-range TLV contents constitute:
o A 32 bit start index. An index of 0 implies the beggining of the
table row.
o A 32 bit end index. A value of 0xFFFFFFFFFFFFFFFF implies the
last entry. XXX: Do we need to define the "end wildcard"?
The response for a table range query will either be:
o The requested table data returned (when at least one referenced
row is available); in such a case, a response with a path pointing
to the table and whose data content contain the row(s) will be
sent to the CE. The data content MUST be encapsulated in
sparsedata TLV. The sparse data TLV content will have the "I" (in
ILV) for each table row indicating the table indices.
o A result TLV when:
* data is absent where the result code of E_NOT_SUPPORTED
(typically returned in current implementations when accessing
an empty table entry) with an english message describing the
nature of the error (refer to Section 4.3).
* When both a path key and path table range are reflected on the
the pathflags, an error code of E_INVALID_FLAGS with an english
message describing the nature of the erro (refer to
Section 4.3).
* other standard ForCES errors (such as ACL constraints trying to
retrieve contents of an unreadable table), accessing unknown
components etc.
4.2. Table Append
We propose using a path flag, F_TABAPPEND(0x4, bit 2) to achieve this
goal.
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When a CE application wishes to append to the table, it will set the
path to a desired table index and set the path flag to F_TABAPPEND.
The FE will first attempt to use the specified index and when
unsuccessful will use an available table row index.
On success or failure to insert the table row, a result TLV will be
returned with the appropriate code. Alternatively a the new
EXTENDED-RESULT-TLV (refer to Section 4.3) maybe returned. The path
of the response will contain the table row index where the table row
was inserted (which the application can then learn).
When successful, an E_SUCCESS return code is sent back to the CE.
Upon failure to append the table row, an appropriate error code is
sent back to the CE.
4.3. Error Codes
We propose a new TLV, EXTENDED-RESULT-TLV (0x118) that will carry
both a result code as currently specified but also a string[N] cause.
This is illustrated in Figure 3.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = EXTENDED-RESULT-TLV | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Result Value | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause string |
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Extended Result TLV
o Like all other ForCES TLVs, the Extended Result TLV is expected to
be 32 bit aligned.
o The Result Value is derived from the same current namespace as
specified in RFC 5810, section 7.1.7.
o It is recommended that the maximum size of the cause string should
not exceed 32 bytes. We do not propose the cause string be
standardized.
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XXX: Backward compatibility may require that we add a FEPO capability
to advertise ability to do extended results so that the CE is able to
interpret the results.
4.4. Bitmap Datatype
TBA
5. IANA Considerations
This document registers two new top Level TLVs and two new path
flags.
The following new TLVs are defined:
o Table-range TLV (type ID 0x117)
o EXTENDED-RESULT-TLV (type ID 0x118)
The following new path flags are defined:
o F_SELTABRANGE (value 0x2 i.e bit 1)
o F_TABAPPEND (value 0x4 i.e bit 2)
6. Security Considerations
TBD
7. References
7.1. Normative References
[RFC3746] Yang, L., Dantu, R., Anderson, T., and R. Gopal,
"Forwarding and Control Element Separation (ForCES)
Framework", RFC 3746, April 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.
[RFC5811] Hadi Salim, J. and K. Ogawa, "SCTP-Based Transport Mapping
Layer (TML) for the Forwarding and Control Element
Separation (ForCES) Protocol", RFC 5811, March 2010.
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[RFC5812] Halpern, J. and J. Hadi Salim, "Forwarding and Control
Element Separation (ForCES) Forwarding Element Model", RFC
5812, March 2010.
7.2. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Author's Address
Jamal Hadi Salim
Mojatatu Networks
Suite 400, 303 Moodie Dr.
Ottawa, Ontario K2H 9R4
Canada
Email: hadi@mojatatu.com
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