Interface to the Routing System (I2RS) Traceability: Framework and Information Model
RFC 7922

Internet Engineering Task Force (IETF) J. Clarke
Request for Comments: 7922 G. Salgueiro
Category: Informational C. Pignataro
ISSN: 2070-1721 Cisco
 June 2016
 Interface to the Routing System (I2RS)
 Traceability: Framework and Information Model
Abstract
 This document describes a framework for traceability in the Interface
 to the Routing System (I2RS) and the information model for that
 framework. It specifies the motivation, requirements, and use cases,
 and defines an information model for recording interactions between
 elements implementing the I2RS protocol. This framework provides a
 consistent tracing interface for components implementing the I2RS
 architecture to record what was done, by which component, and when.
 It aims to improve the management of I2RS implementations, and can be
 used for troubleshooting, auditing, forensics, and accounting
 purposes.
Status of This Memo
 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF). It represents the consensus of the IETF community. It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG). Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7922.
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Copyright Notice
 Copyright (c) 2016 IETF Trust and the persons identified as the
 document authors. All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document. Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document. Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
Table of Contents
 1. Introduction ....................................................3
 2. Terminology and Conventions .....................................3
 3. Motivation ......................................................4
 4. Use Cases .......................................................4
 5. Information Model ...............................................5
 5.1. I2RS Traceability Framework ................................5
 5.2. I2RS Trace Log Fields ......................................7
 5.3. End of Message Marker .....................................11
 6. Examples .......................................................11
 7. Operational Guidance ...........................................11
 7.1. Trace Log Creation ........................................12
 7.2. Trace Log Temporary Storage ...............................12
 7.3. Trace Log Rotation ........................................13
 7.4. Trace Log Retrieval .......................................13
 7.4.1. Retrieval via Syslog ...............................14
 7.4.2. Retrieval via I2RS Information Collection ..........14
 7.4.3. Retrieval via I2RS Pub/Sub .........................14
 8. Security Considerations ........................................15
 9. References .....................................................16
 9.1. Normative References ......................................16
 9.2. Informative References ....................................16
 Acknowledgments ...................................................17
 Authors' Addresses ................................................17
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1. Introduction
 The architecture for the Interface to the Routing System [RFC7921]
 specifies that I2RS clients wishing to retrieve or change the routing
 state on a routing element MUST authenticate to an I2RS agent. The
 I2RS client will have a unique identity it provides for
 authentication, and should provide another opaque identity for
 applications communicating through it. The programming of routing
 state will produce a return code containing the results of the
 specified operation and associated reason(s) for the result. All of
 this is critical information to be used for understanding the history
 of I2RS interactions.
 This document defines the framework necessary to trace those
 interactions between the I2RS client and I2RS agent. It goes on to
 describe use cases for traceability within I2RS. Based on these use
 cases, the document proposes an information model and reporting
 requirements to provide for effective recording of I2RS interactions.
 In this context, effective troubleshooting means being able to
 identify what operation was performed by a specific I2RS client via
 the I2RS agent, what was the result of the operation, and when that
 operation was performed.
2. Terminology and Conventions
 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].
 The architecture specification for I2RS [RFC7921] defines additional
 terms used in this document that are specific to the I2RS domain,
 such as "I2RS agent", "I2RS client", etc. The reader is expected to
 be familiar with the terminology and concepts defined in [RFC7921].
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3. Motivation
 As networks scale and policy becomes an increasingly important part
 of the control plane that creates and maintains the forwarding state,
 operational complexity increases as well. I2RS offers more granular
 and coherent control over policy and control-plane state, but it also
 removes or reduces the locality of the policy that has been applied
 to the control plane at any individual forwarding device. The
 ability to automate and abstract even complex policy-based controls
 highlights the need for an equally scalable traceability function to
 provide recording at event-level granularity of the evolution of the
 routing system compliant with the requirements of I2RS (Section 5 of
 [RFC7920]).
4. Use Cases
 An obvious motivation for I2RS traceability is the need to
 troubleshoot and identify root causes of problems in these
 increasingly complex routing systems. For example, since I2RS is a
 high-throughput multi-channel, full duplex, and highly responsive
 interface, I2RS clients may be performing a large number of
 operations on I2RS agents concurrently or at nearly the same time and
 quite possibly in very rapid succession. As these many changes are
 made, the network reacts accordingly. These changes might lead to a
 race condition, performance issues, data loss, or disruption of
 services. In order to isolate the root cause of these issues, it is
 critical that a network operator or administrator has visibility into
 what changes were made via I2RS at a specific time.
 Some network environments have strong auditing requirements for
 configuration and runtime changes. Other environments have policies
 that require saving logging information for operational or regulatory
 compliance considerations. These requirements therefore demand that
 I2RS provides an account of changes made to network element routing
 systems.
 As I2RS becomes increasingly pervasive in routing environments, a
 traceability model that supports controllable trace log retention
 using a standardized structured data format offers significant
 advantages, such as the ability to create common tools supporting
 automated testing, and facilitates the following use cases:
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 o real-time monitoring and troubleshooting of router events;
 o automated event correlation, trend analysis, and anomaly
 detection;
 o offline (manual or tools-based) analysis of router state evolution
 from the retained trace logs;
 o enhanced network audit, management, and forensic analysis
 capabilities;
 o improved accounting of routing system operations; and
 o providing a standardized format for incident reporting and test
 logging.
5. Information Model
 These sections describe the I2RS traceability information model and
 the details about each of the fields to be logged.
5.1. I2RS Traceability Framework
 This section describes a framework for I2RS traceability based on the
 I2RS Architecture.
 The interaction between the optional network application that drives
 client activity, I2RS client, I2RS agent, the Routing System, and the
 data captured in the I2RS trace log is shown in Figure 1.
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 +---------------+
 +----------------+ |
 |Application | |
 |.............. | | 0 or more Applications
 | Application ID | +
 +----------------+
 ^
 |
 |
 v
 +-------------+
 +-------------+ |
 |I2RS Client | |
 |.............| | 1 or more Clients
 | Client ID | +
 +-------------+
 ^
 |
 |
 v
 +-------------+ +-----------------------------+
 |I2RS Agent |---------------->|Trace Log |
 | | |.............................|
 +-------------+ |Log Entry [1 .. N] |
 | ^ |.............................|
 | | |Event ID |
 | | |Starting Timestamp |
 | | |Request State |
 | | |Client ID |
 | | |Client Priority |
 | | |Secondary ID |
 Operation + | | Result Code |Client Address |
 Op Data | | |Requested Operation |
 | | |Applied Operation |
 | | |Operation Data Present |
 | | |Requested Operation Data |
 | | |Applied Operation Data |
 | | |Transaction ID |
 | | |Result Code |
 | | |Ending Timestamp |
 | | |Timeout Occurred |
 v | |End Of Message |
 +-------------+ +-----------------------------+
 |Routing |
 |System |
 +-------------+
 Figure 1: I2RS Interaction Trace Log Capture
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5.2. I2RS Trace Log Fields
 The following fields comprise an I2RS trace log. These fields ensure
 that each I2RS interaction can be properly traced back to the client
 that made the request at a specific point in time.
 The list below describes the fields captured in the I2RS trace log.
 This list represents a common set of fields that MUST appear in all
 I2RS trace logs. In addition to these fields, I2RS agent
 implementations MAY choose to log additional fields such as I2RS
 client vendor or agent statistics like free memory, performance
 metrics, etc.
 Event ID: This is a unique identifier for each event in the I2RS
 trace log. An event can be a client authenticating with the
 agent, a client to agent operation, or a client disconnecting from
 an agent. Operation events can either be logged atomically upon
 completion (in which case they will have both a Starting and an
 Ending Timestamp field) or they can be logged at the beginning of
 each Request State transition. Since operations can occur from
 the same client at the same time, it is important to have an
 identifier that can be unambiguously associated to a specific
 entry. If each state transition is logged for an operation, the
 same ID MUST be used for each of the Request State log entries.
 In this way, the life of a request can be easily followed in the
 I2RS trace log. Beyond the requirement that the Event ID MUST be
 unique for each event, the specific type and value is left up to
 the implementation.
 Starting Timestamp: The specific time at which the I2RS operation
 enters the specified Request State within the agent. If the log
 entry covers the entire duration of the request, then this will be
 the time that it was first received by the agent. This field MUST
 be present in all entries that specify the beginning of the state
 transition, as well as those entries that log the entire duration
 of the request. The time is passed in the full timestamp format
 [RFC3339], including the date and offset from Coordinated
 Universal Time (UTC). Given that many I2RS operations can occur
 in rapid succession, the fractional seconds element of the
 timestamp MUST be used to provide adequate granularity.
 Fractional seconds SHOULD be expressed with at least three
 significant digits in second.microsecond format.
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 Request State: The state of the given operation within the I2RS
 agent state machine at the specified Starting or Ending
 Timestamps. The I2RS agent SHOULD generate a log entry at the
 moment a request enters and exits a state. Upon entering a new
 state, the log entry will have a Starting Timestamp set to the
 time of entry and no Ending Timestamp. Upon exiting a state, the
 log entry will have an Ending Timestamp set to the time of exit
 and no Starting Timestamp. The progression of the request through
 its various states can be linked using the Event ID. The states
 can be one of the following values:
 PENDING: The request has been received and queued for
 processing.
 IN PROCESS: The request is currently being handled by the I2RS
 agent.
 COMPLETED: The request has reached a terminal point.
 Every state transition SHOULD be logged unless doing so will put
 an undue performance burden on the I2RS agent. However, an entry
 with the Request State set to COMPLETED MUST be logged for all
 operations. If the COMPLETED state is the only entry for a given
 request, then it MUST have both Starting and Ending Timestamps
 that cover the entire duration of the request from ingress to the
 agent until completion.
 Client Identity: The I2RS client identity used to authenticate the
 client to the I2RS agent.
 Client Priority: The I2RS client priority assigned by the access
 control model that authenticates the client. For example, this
 can be set by the Network Configuration Protocol (NETCONF) Access
 Control Model (NACM) as described in [RFC6536].
 Secondary Identity: This is an opaque identity that may be known to
 the client from a controlling network application. This is used
 to trace the network application driving the actions of the
 client. The client may not provide this identity to the agent if
 there is no external network application driving the client.
 However, this field MUST be logged even if the client does not
 provide a Secondary Identity. In that case, the field will be
 logged with an empty value.
 Client Address: This is the network address of the client that
 connected to the agent. For example, this may be an IPv4 or an
 IPv6 address.
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 Requested Operation: This is the I2RS operation that was requested
 to be performed. For example, this may be an add route operation
 if a route is being inserted into a routing table. This may not
 be the operation that was actually applied to the agent.
 In the case of a client authenticating to the agent, the Requested
 Operation MUST be "CLIENT AUTHENTICATE". In the case of a client
 disconnecting from the agent, the Requested Operation MUST be
 "CLIENT DISCONNECT".
 Applied Operation: This is the I2RS operation that was actually
 performed. This can differ from the Requested Operation in cases
 where the agent cannot satisfy the Requested Operation. This
 field may not be logged unless the Request State is COMPLETED.
 Operation Data Present: This is a Boolean field that indicates
 whether or not additional per-Operation Data is present.
 Requested Operation Data: This field comprises the data passed to
 the agent to complete the desired operation. For example, if the
 operation is a route add operation, the Operation Data would
 include the route prefix, prefix length, and next-hop information
 to be inserted as well as the specific routing table to which the
 route will be added. If Operation Data is provided, then the
 Operation Data Present field MUST be set to TRUE. Some operations
 may not provide operation data. In those cases, the Operation
 Data Present field MUST be set to FALSE, and this field MUST be
 empty. This may not represent the data that was used for the
 operation that was actually applied on the agent.
 When a client authenticates to the agent, the Requested Operation
 Data MUST contain the client priority. Other attributes such as
 credentials used for authentication MAY be logged.
 Applied Operation Data: This field comprises the data that was
 actually applied as part of the Applied Operation. If the agent
 cannot satisfy the Requested Operation with the Requested
 Operation Data, then this field can differ from the Requested
 Operation Data. This field will be empty unless the Requested
 Operation Data was specified. This field may not be logged unless
 the Request State is COMPLETED.
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 Transaction ID: The Transaction Identity represents that this
 particular operation is part of a long-running I2RS transaction
 that can consist of multiple, related I2RS operations. Using this
 value, one can relate multiple log entries together as they are
 part of a single, overall I2RS operation. This is an optional
 field that may not be logged unless the event is part of a long-
 running transaction.
 Result Code: This field holds the result of the operation once the
 Request State is COMPLETED. In the case of Routing Information
 Base (RIB) operations, this MUST be the return code as specified
 in Section 4 of [RIBINFO]. The operation may not complete with a
 result code in the case of a timeout. If the operation fails to
 complete, it MUST still log the attempted operation with an
 appropriate result code.
 Timeout Occurred: This is a Boolean field that indicates whether or
 not a timeout occurred in the operation. When this is true, the
 value of the Ending Timestamp MUST be set to the time the agent
 recorded for the timeout occurrence. This field may not be logged
 unless the Request State is COMPLETED.
 Ending Timestamp: The specific time at which the I2RS operation
 exits the specified Request State within the I2RS agent. If the
 log entry covers the entire duration of the request, then this
 will be the time that the request reached a terminal point within
 the agent. This field MUST be present in all entries that specify
 the ending of the state transition, as well as those entries that
 log the entire duration of the request. The time is passed in the
 full timestamp format [RFC3339], including the date and offset
 from Coordinated Universal Time (UTC). See the description for
 Starting Timestamp above for the proper format of the Ending
 Timestamp.
 End Of Message: Each log entry SHOULD have an appropriate End Of
 Message (EOM) indicator. See Section 5.3 below for more details.
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5.3. End of Message Marker
 Because of variability within I2RS trace log fields, implementors
 MUST use a format-appropriate End Of Message (EOM) indicator in order
 to signify the end of a particular record. That is, regardless of
 format, the I2RS trace log MUST provide a distinct way of
 distinguishing between the end of one record and the beginning of
 another. For example, in a linear-formatted log (similar to a
 syslog) the EOM marker may be a newline character. In an XML-
 formatted log, the schema would provide for element tags that denote
 the beginning and end of records. In a JSON-formatted log, the
 syntax would provide record separation (likely by comma-separated
 array elements).
6. Examples
 This section shows a sample of what the fields and values could look
 like.
 Event ID: 1
 Starting Timestamp: 2013年09月03日T12:00:01.21+00:00
 Request State: COMPLETED
 Client ID: 5CEF1870-0326-11E2-A21F-0800200C9A66
 Client Priority: 100
 Secondary ID: com.example.RoutingApp
 Client Address: 2001:db8:c0c0::2
 Requested Operation: ROUTE_ADD
 Applied Operation: ROUTE_ADD
 Operation Data Present: TRUE
 Requested Operation Data: PREFIX 2001:db8:feed:: PREFIX-LEN 64
 NEXT-HOP 2001:db8:cafe::1
 Applied Operation Data: PREFIX 2001:db8:feed:: PREFIX-LEN 64
 NEXT-HOP 2001:db8:cafe::1
 Transaction ID: 2763461
 Result Code: SUCCESS(0)
 Timeout Occurred: FALSE
 Ending Timestamp: 2013年09月03日T12:00:01.23+00:00
7. Operational Guidance
 Specific operational procedures regarding temporary log storage,
 rollover, retrieval, and access of I2RS trace logs is out of scope
 for this document. Organizations employing I2RS trace logging are
 responsible for establishing proper operational procedures that are
 appropriately suited to their specific requirements and operating
 environment. In this section, we only provide fundamental and
 generalized operational guidelines that are implementation
 independent.
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7.1. Trace Log Creation
 The I2RS agent interacts with the Routing and Signaling functions of
 the Routing Element. Since the I2RS agent is responsible for
 actually making the routing changes on the associated network device,
 it creates and maintains a log of operations that can be retrieved to
 troubleshoot I2RS-related impact to the network. Changes that occur
 to the network element's local configuration outside of the I2RS
 protocol that preempt I2RS state will only be logged if the network
 element notifies the I2RS agent.
7.2. Trace Log Temporary Storage
 The trace information may be temporarily stored either in an
 in-memory buffer or as a file local to the agent. Care should be
 given to the number of I2RS operations expected on a given agent so
 that the appropriate storage medium is used, and to maximize the
 effectiveness of the log while not impacting the performance and
 health of the agent. client requests may not always be processed
 synchronously or within a bounded time period. Consequently, to
 ensure that trace log fields, such as "Operation" and "Result Code",
 are part of the same trace log record, buffering of the trace log
 entries may be required. This buffering may result in additional
 resource load on the agent and the network element.
 Section 7.3 discusses rotating the trace log in order to preserve the
 operation history without exhausting agent or network device
 resources. It is perfectly acceptable, therefore, to use both an
 in-memory buffer for recent operations while rotating or archiving
 older operations to a local file.
 It is outside the scope of this document to specify the
 implementation details (i.e., size, throughput, data protection,
 etc.) for the physical storage of the I2RS log file. In terms of
 data retention, attention should be paid to the length of time that
 the I2RS trace log data is kept when that data contains security- or
 privacy-sensitive attributes. The longer this data is retained, the
 higher the impact if it were to be leaked. It is also possible that
 legislation may impose some additional requirements on the minimum
 and/or maximum durations for which some kinds of data may be
 retained.
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7.3. Trace Log Rotation
 In order to prevent the exhaustion of resources on the I2RS agent or
 its associated network device, it is RECOMMENDED that the I2RS agent
 implements trace log rotation. The details on how this is achieved
 are left to the implementation and are outside the scope of this
 document. However, it should be possible to do a file rotation based
 on either the time or size of the current trace log. If file
 rollover is supported, multiple archived log files should be
 supported in order to maximize the troubleshooting and accounting
 benefits of the trace log.
7.4. Trace Log Retrieval
 Implementors are free to provide their own, proprietary interfaces
 and develop custom tools to retrieve and display the I2RS trace log.
 These may include the display of the I2RS trace log as command-line
 interface (CLI) output. However, a key intention of defining this
 information model is to establish a vendor-agnostic and consistent
 interface to collect I2RS trace data. Correspondingly, retrieval of
 the data should also be made vendor-agnostic.
 Despite the fact that export of I2RS trace log information could be
 an invaluable diagnostic tool for off-box analysis, exporting this
 information MUST NOT interfere with the ability of the agent to
 process new incoming operations.
 The following three sections describe potential ways the trace log
 can be accessed. The use of I2RS pub/sub for accessing trace log
 data is mandatory-to-implement, while others are optional.
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7.4.1. Retrieval via Syslog
 The syslog protocol [RFC5424] is a standard way of sending event
 notification messages from a host to a collector. However, the
 protocol does not define any standard format for storing the
 messages, and thus implementors of I2RS tracing would be left to
 define their own format. So, while the data contained within the
 syslog message would adhere to this information model, and may be
 consumable by a human operator, it would not be easily parseable by a
 machine. Syslog MAY be employed as a means of retrieving or
 disseminating the I2RS trace log contents.
 If syslog is used for trace log retrieval, then existing logging
 infrastructure and capabilities of syslog [RFC5424] should be
 leveraged without the need to define or extend existing formats.
 That is, the various fields described in Section 5.2 SHOULD be
 modeled and encoded as Structured Data Elements (referred to as
 "SD-ELEMENT"), as described in Section 6.3.1 of [RFC5424].
7.4.2. Retrieval via I2RS Information Collection
 Section 7.7 of the I2RS architecture [RFC7921] defines a mechanism
 for information collection. The information collected includes
 obtaining a snapshot of a large amount of data from the network
 element. It is the intent of I2RS to make this data available in an
 implementor-agnostic fashion. Therefore, the I2RS trace log SHOULD
 be made available via the I2RS information collection mechanism
 either as a single snapshot or via a subscription stream.
7.4.3. Retrieval via I2RS Pub/Sub
 Section 7.6 of the I2RS architecture [RFC7921] goes on to describe
 notification mechanisms for a feed of changes happening within the
 I2RS layer. Specifically, the requirements for a publish-subscribe
 system for I2RS are defined in [RFC7923]. I2RS agents MUST support
 publishing I2RS trace log information to that feed as described in
 [RFC7923]. Subscribers would then receive a live stream of I2RS
 interactions in trace log format and could flexibly choose to do a
 number of things with the log messages. For example, the subscribers
 could log the messages to a datastore, aggregate, and summarize
 interactions from a single client, etc. The full range of potential
 activities is virtually limitless and the details of how they are
 performed are outside the scope of this document, however.
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8. Security Considerations
 The I2RS trace log, like any log file, reveals the state of the
 entity producing it as well as the identifying information elements
 and detailed interactions of the system containing it. The
 information model described in this document does not itself
 introduce any security issues, but it does define the set of
 attributes that make up an I2RS log file. These attributes may
 contain sensitive information, and thus should adhere to the
 security, privacy, and permission policies of the organization making
 use of the I2RS log file.
 It is outside the scope of this document to specify how to protect
 the stored log file, but it is expected that adequate precautions and
 security best practices such as disk encryption, appropriately
 restrictive file/directory permissions, suitable hardening and
 physical security of logging entities, mutual authentication,
 transport encryption, channel confidentiality, and channel integrity
 if transferring log files. Additionally, the potentially sensitive
 information contained in a log file SHOULD be adequately anonymized
 or obfuscated by operators to ensure its privacy.
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9. References
9.1. Normative References
 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
 Requirement Levels", BCP 14, RFC 2119,
 DOI 10.17487/RFC2119, March 1997,
 <http://www.rfc-editor.org/info/rfc2119>.
 [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
 Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
 <http://www.rfc-editor.org/info/rfc3339>.
 [RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424,
 DOI 10.17487/RFC5424, March 2009,
 <http://www.rfc-editor.org/info/rfc5424>.
 [RFC7921] Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
 Nadeau, "An Architecture for the Interface to the Routing
 System", RFC 7921, DOI 10.17487/RFC7921, June 2016,
 <http://www.rfc-editor.org/info/rfc7921>.
 [RFC7923] Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
 for Subscription to YANG Datastores", RFC 7923,
 DOI 10.17487/RFC7923, June 2016.
9.2. Informative References
 [RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration
 Protocol (NETCONF) Access Control Model", RFC 6536,
 DOI 10.17487/RFC6536, March 2012,
 <http://www.rfc-editor.org/info/rfc6536>.
 [RFC7920] Atlas, A., Ed., Nadeau, T., Ed., and D. Ward, "Problem
 Statement for the Interface to the Routing System",
 RFC 7923, DOI 10.17487/RFC7923, June 2016,
 <http://www.rfc-editor.org/info/rfc7920>.
 [RIBINFO] Bahadur, N., Ed., Kini, S., Ed., and J. Medved, "Routing
 Information Base Info Model", Work in Progress,
 draft-ietf-i2rs-rib-info-model-08, October 2015.
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Acknowledgments
 The authors would like to thank Alia Atlas for her initial feedback
 and overall support for this work. Additionally, the authors
 acknowledge Alvaro Retana, Russ White, Matt Birkner, Jeff Haas, Joel
 Halpern, Dean Bogdanovich, Ignas Bagdonas, Nobo Akiya, Kwang-koog
 Lee, Sue Hares, Mach Chen, Alex Clemm, Stephen Farrell, Benoit
 Claise, Les Ginsberg, Suresh Krishnan, and Elwyn Davies for their
 reviews, contributed text, and suggested improvements to this
 document.
Authors' Addresses
 Joe Clarke
 Cisco Systems, Inc.
 7200-12 Kit Creek Road
 Research Triangle Park, NC 27709
 United States
 Phone: +1-919-392-2867
 Email: jclarke@cisco.com
 Gonzalo Salgueiro
 Cisco Systems, Inc.
 7200-12 Kit Creek Road
 Research Triangle Park, NC 27709
 United States
 Email: gsalguei@cisco.com
 Carlos Pignataro
 Cisco Systems, Inc.
 7200-11 Kit Creek Road
 Research Triangle Park, NC 27709
 United States
 Email: cpignata@cisco.com
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