Keywords: serviceability, SDN, resilience, robustness, network programmability, network API, application control, service-aware networking, automation
Independent Submission S. Vinapamula
Request for Comments: 7767 Juniper Networks
Category: Informational S. Sivakumar
ISSN: 2070-1721 Cisco Systems
M. Boucadair
Orange
T. Reddy
Cisco
February 2016
Application-Initiated Check-Pointing via the Port Control Protocol (PCP)
Abstract
This document specifies a mechanism for a host to indicate via the
Port Control Protocol (PCP) which connections should be protected
against network failures. These connections will then be subject to
high-availability mechanisms enabled on the network side.
This approach assumes that applications and/or users have more
visibility about sensitive connections than any heuristic that can be
enabled on the network side to guess which connections should be
check-pointed.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
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/rfc7767.
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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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Note . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Issues with the Existing Implementations . . . . . . . . . . 4
3. CHECKPOINT_REQUIRED PCP Option . . . . . . . . . . . . . . . 4
3.1. Format . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Operation . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Sample Use Cases . . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Additional Considerations . . . . . . . . . . . . . 11
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
The risk of Internet service disruption is critical in service
providers and enterprise networking environments. Such a risk is
often mitigated with the introduction of active/backup systems. Such
designs not only contribute to minimize the risk of service
disruption, but also facilitate maintenance operations (e.g., hitless
hardware or software upgrades).
In addition, the nature of some connections leads to the
establishment and the maintenance of connection-specific states by
some of the network functions invoked when the connection is
established. During active/backup failover in case of a network
failure, the said states need to be check-pointed by the backup
system. Additional issues are discussed in Section 2.
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Heuristics based on the protocol, mapping lifetime, etc., are used in
the network to elect which connections need to be check-pointed
(e.g., by means of high-availability (HA) techniques). This document
advocates for an application-initiated approach that would allow
applications and/or users to signal to the network which of their
connections are critical.
Within this document, "check-pointing" refers to a process of state
replication and synchronization between active and backup PCP-
controlled devices. When the active PCP-controlled device fails, the
backup PCP-controlled device will take over all the existing
established sessions that were check-pointed. This process is
transparent to internal hosts.
This document specifies how PCP [RFC6887] can be extended to indicate
which connection should be check-pointed for high availability
(Section 3). A set of use cases are provided for illustrative
purposes in Section 4. This document does not make any assumptions
about the PCP-controlled device that will process the PCP-formatted
signaling information from PCP clients. These devices are likely to
be flow aware.
The approach in this document is aligned with the networking trends
advocating for open network APIs to interact with applications/
services (e.g., [RFC7149]). For instance, the decision-making
process about policy on the network side will be enriched with
information provided by applications using PCP.
1.1. Note
The CHECKPOINT_REQUIRED PCP option (Section 3) is defined in the
"Specification Required" range (see Section 6). In order to be
assigned a code point in that range, a permanent publication is
required as per Section 4.1 of [RFC5226]. Publication of an RFC is
an ideal means of achieving this requirement and also to ease
interoperability.
Note, this work was presented to the Port Control Protocol (PCP) WG,
but there was no consensus to define this option in the "Standards
Action" range despite positive feedback that was received from the
working group. Technical comments that were received during PCP
meetings and those received on the mailing list were addressed.
1.2. 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 RFC 2119 [RFC2119].
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2. Issues with the Existing Implementations
Regardless of the selected technology or design like HA-based
designs, reliably securing connections is expensive in terms of
memory, CPU usage, and other resources. Also, check-pointing may not
be required for all connections, as all connections may not be
critical. But, this leaves a challenge to identify what connections
to check-point.
Typically, this is addressed by identifying long-lived connections
and check-pointing the state of only those connections that lived
long enough, to the backup for service continuity.
However, check-pointing long-lived connections raises the following
issues:
1. It is hard for a network to identify (or guess) which connection
is (business) critical. This characterization is often customer-
specific: a flow can be sensitive for a User #1, while it is not
for another User #2. Furthermore, this characterization can vary
over time: a flow can be sensitive during hour X, while it is not
during other times.
2. Heuristics are not deterministic.
3. A potentially long-lived connection may experience disruption
upon failure of the active system, but before it is check-
pointed.
4. A connection may not be long-lived but it may be critical, e.g.,
for Voice over IP (VoIP) conversations.
5. Likewise, not all long-lived connections are deemed critical: for
example, connections that pertain to free Internet services are
usually considered not critical compared to the equivalent
connections for paid services. Only the latter need to be check-
pointed.
3. CHECKPOINT_REQUIRED PCP Option
3.1. Format
The solution is based on the assumption that an application or user
is the best judge of which of its connections are critical.
An application or user may explicitly identify the connections that
need to be check-pointed by means of a PCP client, using the
CHECKPOINT_REQUIRED option as described in Figure 1.
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The entry to be backed up is indicated by the content of a MAP or
PEER message.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Option Code=192| Reserved | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Name: CHECKPOINT_REQUIRED
Number: 192
Purpose: Indicate if an entry needs to be check-pointed.
Valid for Opcodes: MAP, PEER
Length: 0.
May appear in: Request and response.
Maximum occurrences: 1.
Figure 1: CHECKPOINT_REQUIRED PCP Option
The description of the fields is as follows:
o Option Code: 192 (see Section 6).
o Reserved: This field is initialized as specified in Section 7.3 of
[RFC6887].
o Option Length: 0. This means no data is included in the option.
An application or user can take advantage of this PCP option to
explicitly indicate which of the connections need to be check-pointed
and should not be disrupted. The processing of this option by the
PCP server will then yield the check-pointing of the corresponding
states by the relevant devices or functions dynamically controlled by
the PCP server.
Communication between application/user and PCP client is
implementation specific.
3.2. Operation
Support of the CHECKPOINT_REQUIRED option by PCP servers and PCP
clients is optional. This option (Code 192; see Figure 1) may be
included in a PCP MAP or PEER request to indicate a connection is to
be protected against network failures.
There is a risk that every PCP client may wish to check-point every
connection; this can potentially load the system. Administration
SHOULD restrict the number of connections that can be elected to be
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backed up and the rate of check-pointing per network attachment point
(e.g., Customer Premises Equipment (CPE), host). To that aim, the
PCP server should unambiguously identify the network attachment point
a PCP client belongs to. For example, the PCP server may rely on the
PCP identity [RFC7652], the assigned prefix to a CPE or host, the
subscriber-mask [PREFIX-BINDING], or other identification means.
The PCP client includes a CHECKPOINT_REQUIRED option in a MAP or PEER
request to signal that the corresponding mapping is to be protected.
If the PCP client does not receive a CHECKPOINT_REQUIRED option in
response to a PCP request that enclosed the CHECKPOINT_REQUIRED
option, this means that either the PCP server does not support the
option, or the PCP server is configured to ignore the option, or the
PCP server cannot satisfy the request expressed in this option (e.g.,
because of a lack of resources).
If the CHECKPOINT_REQUIRED option is not included in the PCP client
request, the PCP server MUST NOT include the CHECKPOINT_REQUIRED
option in the associated response.
When the PCP server receives a CHECKPOINT_REQUIRED option, the PCP
server checks if it can honor this request depending on whether
resources are available for check-pointing. If there are no
resources available for check-pointing, but there are resources
available to honor the MAP or PEER request, a response is sent back
to the PCP client without including the CHECKPOINT_REQUIRED option
(i.e., the request is processed as any MAP or PEER request that does
not convey a CHECKPOINT_REQUIRED option). If check-pointing
resources are still available and the quota for this PCP client has
not been reached, the PCP server tags the corresponding entry as
eligible to the HA mechanism and sends back the CHECKPOINT_REQUIRED
option in the positive answer to the PCP client.
To update the check-pointing behavior of a mapping maintained by the
PCP server, the PCP client generates a PCP MAP or PEER renewal
request that includes a CHECKPOINT_REQUIRED option to indicate this
mapping has to be check-pointed or that doesn't include a
CHECKPOINT_REQUIRED option to indicate this mapping does not need be
check-pointed anymore. Upon receipt of the PCP request, the PCP
server proceeds with the same operations to validate a MAP or PEER
request to update an existing mapping. If validation checks are
passed, the PCP server updates the check-point flag associated with
that mapping accordingly (i.e., it is set if a CHECKPOINT_REQUIRED
option was included in the update request or it is cleared if no
CHECKPOINT_REQUIRED option was included), and the PCP server returns
the response to the PCP client accordingly.
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What information to check-point and how to check-point are outside
the scope of this document and are left for implementations. Also,
the mechanism for users or applications to indicate check-pointing in
a PCP request may be automatic, semiautomatic, or require human
intervention. This behavior is also left for application
implementations. For managed CPEs, a service provider may influence
what connections are to be check-pointed.
For honored requests, it is RECOMMENDED to check-point state on
backup before a response is sent to the PCP client.
4. Sample Use Cases
Below are provided some examples for illustrative purposes:
Example 1: Consider a streaming service such as live TV
broadcasting, or any other media streaming, that supports check-
pointing signaling functionality. Suppose this application is
installed in three hosts A, B and C. For A, the application is
critical and should not be interrupted, while for B it is not.
While for C, only some programs are of interest. At the time of
installing this application's software, corresponding preferences
can be provisioned. When the application starts streaming:
* All the flows associated with the streaming application are
critical for A. Limiting the number of flows to be backed up
will ensure that host doesn't exceed the user's limit.
* For B, none of these flows are critical for check-pointing.
The CHECKPOINT_REQUIRED option is not included in the PCP
requests.
* For C, the user is invited to interact with the application by
means of a configuration option that is provided to dynamically
select which streaming to check-point, based on the user's
interest.
Example 2: Consider a streaming service offered by a provider.
Suppose three levels of subscriptions are offered by that
provider, e.g., gold, silver, and bronze. To guarantee a certain
level of quality of service for each subscription, policies are
configured such that:
* All flows associated with a gold subscription should be check-
pointed.
* Only some flows associated with a silver subscription are
check-pointed.
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* None of the flows associated with a bronze subscription are
check-pointed.
When a user invokes the streaming service, he/she may fall into
one of those buckets, and according to the configured policy, his/
her associated streaming flows are automatically check-pointed.
Login credentials can be used as a trigger to determine the
subscription level (and therefore the associated check-pointing
behavior).
Example 3: Consider a VoIP application that is able to request that
its flows be check-pointed. No matter what is configured by the
user, some calls such as emergency calls should be check-pointed.
The application has to identify such calls.
Example 4: In the context of an enterprise network, applications are
customized by the administrator. Instructions about whether a
CHECKPOINT_REQUIRED option is to be included are determined by the
administrator. Only the subset of applications identified by the
administrator will make use of this option in conformance with the
enterprise network's management policies. Any misbehavior can be
considered as abuse.
In order to prevent every application from including a
CHECKPOINT_REQUIRED option in its PCP requests, the following items
are assumed:
o Applications may be delivered with some default settings for
check-pointing, and these settings should be programmable by end
user.
o Exposing and enforcing these settings is application specific.
o The end user may customize these settings based on the
requirements.
5. Security Considerations
PCP-related security considerations are discussed in [RFC6887].
The CHECKPOINT_REQUIRED option can be used by an attacker to identify
critical flows; this is sensitive from a privacy standpoint. Also,
an attacker can cause critical flows to not be check-pointed by
stripping the CHECKPOINT_REQUIRED option or by consuming the quota by
adding the option to other flows.
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These two issues can be mitigated if the network on which the PCP
messages are to be sent is fully trusted. Means to defend against
attackers who can intercept packets between the PCP server and the
PCP client should be enabled. In some deployments, access control
lists (ACLs) can be installed on the PCP client, PCP server, and the
network between them, so those ACLs allow only communications between
trusted PCP elements. If the networking environment between the PCP
client and the PCP server is not secure, PCP authentication [RFC7652]
MUST be enabled.
A network device can always override the end-user signaling, i.e.,
what is signaled by the PCP client, if the instructions conflict with
the network policies.
6. IANA Considerations
The following PCP Option Code has been allocated in the
"Specification Required" range of the "PCP Options" registry
(http://www.iana.org/assignments/pcp-parameters):
192 CHECKPOINT_REQUIRED (see Section 3.1)
7. References
7.1. 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>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013,
<http://www.rfc-editor.org/info/rfc6887>.
[RFC7652] Cullen, M., Hartman, S., Zhang, D., and T. Reddy, "Port
Control Protocol (PCP) Authentication Mechanism",
RFC 7652, DOI 10.17487/RFC7652, September 2015,
<http://www.rfc-editor.org/info/rfc7652>.
7.2. Informative References
[PREFIX-BINDING]
Vinapamula, S. and M. Boucadair, "Recommendations for
Prefix Binding in the Softwire DS-Lite Context", Work in
Progress, draft-vinapamula-softwire-dslite-prefix-
binding-12, October 2015.
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[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC7149] Boucadair, M. and C. Jacquenet, "Software-Defined
Networking: A Perspective from within a Service Provider
Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,
<http://www.rfc-editor.org/info/rfc7149>.
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Appendix A. Additional Considerations
It was tempting to include additional fields in the option but this
would lead to a more complex design that is not justified. For
example, we considered the following.
o Define a dedicated field to indicate a priority level. This
priority is intended to be used by the PCP server as a hint when
processing a request with a CHECKPOINT_REQUIRED option.
Nevertheless, an application may systematically choose to set the
priority level to the highest value so that it increases its
chance to be serviced!
o Return a more granular failure error code to the requesting PCP
client. However, this would require extra processing at both the
PCP client and server sides for handling the various error codes
without any guarantee that the PCP client would have its mappings
check-pointed.
Acknowledgments
Thanks to Reinaldo Penno, Stuart Cheshire, Dave Thaler, Prashanth
Patil, and Christian Jacquenet for their comments.
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Authors' Addresses
Suresh Vinapamula
Juniper Networks
1194 North Mathilda Avenue
Sunnyvale, CA 94089
United States
Phone: +1 408 936 5441
Email: sureshk@juniper.net
Senthil Sivakumar
Cisco Systems
7100-8 Kit Creek Road
Research Triangle Park, NC 27760
United States
Phone: +1 919 392 5158
Email: ssenthil@cisco.com
Mohamed Boucadair
Orange
Rennes 35000
France
Email: mohamed.boucadair@orange.com
Tirumaleswar Reddy
Cisco Systems, Inc.
Cessna Business Park, Varthur Hobli
Sarjapur Marathalli Outer Ring Road
Bangalore, Karnataka 560103
India
Email: tireddy@cisco.com
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