Internet DRAFT - draft-ietf-mpls-sfl-framework
draft-ietf-mpls-sfl-framework
MPLS Working Group S. Bryant
Internet-Draft Futurewei Technologies Inc
Intended status: Standards Track M. Chen
Expires: April 5, 2021 Huawei
G. Swallow
Southend Technical Center
S. Sivabalan
Ciena Corporation
G. Mirsky
ZTE Corp.
October 02, 2020
Synonymous Flow Label Framework
draft-ietf-mpls-sfl-framework-11
Abstract
RFC 8372 (MPLS Flow Identification Considerations) describes the
requirement for introducing flow identities within the MPLS
architecture. This document describes a method of accomplishing this
by using a technique called Synonymous Flow Labels in which labels
which mimic the behaviour of other labels provide the identification
service. These identifiers can be used to trigger per-flow
operations on the packet at the receiving label switching router.
Status of This Memo
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This Internet-Draft will expire on April 5, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
3. Synonymous Flow Labels . . . . . . . . . . . . . . . . . . . 3
4. User Service Traffic in the Data Plane . . . . . . . . . . . 4
4.1. Application Label Present . . . . . . . . . . . . . . . . 4
4.1.1. Setting TTL and the Traffic Class Bits . . . . . . . 5
4.2. Single Label Stack . . . . . . . . . . . . . . . . . . . 5
4.2.1. Setting TTL and the Traffic Class Bits . . . . . . . 6
4.3. Aggregation of SFL Actions . . . . . . . . . . . . . . . 6
5. Equal Cost Multipath Considerations . . . . . . . . . . . . . 7
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Contributing Authors . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
[RFC8372] (MPLS Flow Identification Considerations) describes the
requirement for introducing flow identities within the MPLS
architecture. This document describes a method of providing the
required identification by using a technique called Synonymous Flow
Labels (SFL) in which labels which mimic the behaviour of other MPLS
labels provide the identification service. These identifiers can be
used to trigger per-flow operations on the packet at the receiving
label switching router.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
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14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Synonymous Flow Labels
An SFL is defined to be a label that causes exactly the same
behaviour at the egress Label Edge Router (LER) as the label it
replaces, except that it also causes one or more additional actions
that have been previously agreed between the peer LERs to be executed
on the packet. There are many possible additional actions such as
the measurement of the number of received packets in a flow,
triggering an IP Flow Information Export (IPFIX) [RFC7011] capture,
triggering other types of Deep Packet Inspection, or identification
of the packet source. In, for example, a Performance Monitoring (PM)
application, the agreed action could be the recording of the receipt
of the packet by incrementing a packet counter. This is a natural
action in many MPLS implementations, and where supported this permits
the implementation of high quality packet loss measurement without
any change to the packet forwarding system.
To illustrate the use of this technology, we start by considering the
case where there is an "application" label in the MPLS label stack.
As a first example, let us consider a pseudowire (PW) [RFC3985] on
which it is desired to make packet loss measurements. Two labels,
synonymous with the PW labels, are obtained from the egress
terminating provider edge (T-PE). By alternating between these SFLs
and using them in place of the PW label, the PW packets may be
batched for counting without any impact on the PW forwarding behavior
[RFC8321] (note that strictly only one SFL is needed in this
application, but that is an optimization that is a matter for the
implementor). The method of obtaining these additional labels is
outside the scope of this text, however, one control protocol that
provides a method of obtaining SFLs is described in
[I-D.bryant-mpls-sfl-control].
Now consider an MPLS application that is multi-point to point such as
a VPN. Here it is necessary to identify a packet batch from a
specific source. This is achieved by making the SFLs source
specific, so that batches from one source are marked differently from
batches from another source. The sources all operate independently
and asynchronously from each other, independently coordinating with
the destination. Each ingress LER is thus able to establish its own
SFL to identify the sub-flow and thus enable PM per flow.
Finally we need to consider the case where there is no MPLS
application label such as occurs when sending IP over an LSP, i.e.
there is a single label in the MPLS label stack. In this case
introducing an SFL that was synonymous with the LSP label would
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introduce network-wide forwarding state. This would not be
acceptable for scaling reasons. We therefore have no choice but to
introduce an additional label. Where penultimate hop popping (PHP)
is in use, the semantics of this additional label can be similar to
the LSP label. Where PHP is not in use, the semantics are similar to
an MPLS explicit NULL [RFC3032]. In both of these cases the label
has the additional semantics of the SFL.
Note that to achieve the goals set out above, SFLs need to be
allocated from the platform label table.
4. User Service Traffic in the Data Plane
As noted in Section 3 it is necessary to consider two cases:
1. Application label is present
2. Single label stack
4.1. Application Label Present
Figure 1 shows the case in which both an LSP label and an application
label are present in the MPLS label stack. Traffic with no SFL
function present runs over the "normal" stack, and SFL-enabled flows
run over the SFL stack with the SFL used to indicate the packet
batch.
+-----------------+ +-----------------+
| LSP | | LSP |
| Label | | Label |
| (May be PHPed) | | (May be PHPed) |
+-----------------+ +-----------------+
| | | |
| Application | | Synonymous Flow |
| Label | | Label |
+-----------------+ <= BoS +-----------------+ <= Bottom of stack
| | | |
| Payload | | Payload |
| | | |
+-----------------+ +-----------------+
"Normal" Label Stack Label Stack with SFL
Figure 1: Use of Synonymous Labels In A Two Label MPLS Label Stack
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At the egress LER the LSP label is popped (if present). Then the SFL
is processed executing both the synonymous function and the
corresponding application function.
4.1.1. Setting TTL and the Traffic Class Bits
The TTL and the Traffic Class bits [RFC5462] in the SFL label stack
entry (LSE) would normally be set to the same value as would have
been set in the label that the SFL is synonymous with. However, it
is recognized that if there is an application need these fields in
the SFL Label Stack Entry (LSE) MAY be set these to some other value.
An example would be where it was desired to cause the SFL to trigger
an action in the TTL expiry exception path as part of the label
action.
4.2. Single Label Stack
Figure 2 shows the case in which only an LSP label is present in the
MPLS label stack. Traffic with no SFL function present runs over the
"normal" stack and SFL-enabled flows run over the SFL stack with the
SFL used to indicate the packet batch. However in this case it is
necessary for the ingress Label Edge Router (LER) to first push the
SFL and then to push the LSP label.
+-----------------+
| LSP |
| Label |
| (May be PHPed) |
+-----------------+ +-----------------+
| LSP | | | <= Synonymous with
| Label | | Synonymous Flow | Explicit NULL
| (May be PHPed) | | Label |
+-----------------+ <= BoS +-----------------+ <= Bottom of stack
| | | |
| Payload | | Payload |
| | | |
+-----------------+ +-----------------+
"Normal" Label Stack Label Stack with SFL
Figure 2: Use of Synonymous Labels In A Single Label MPLS Label Stack
At the receiving Label Switching Router (LSR) it is necessary to
consider two cases:
1. Where the LSP label is still present
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2. Where the LSP label is penultimate hop popped
If the LSP label is present, it is processed exactly as it would
normally processed and then it is popped. This reveals the SFL,
which, in the case of [RFC6374] measurements, is simply counted and
then discarded. In this respect the processing of the SFL is
synonymous with an MPLS Explicit NULL. As the SFL is the bottom of
stack, the IP packet that follows is processed as normal.
If the LSP label is not present due to PHP action in the upstream
LSR, two almost equivalent processing actions can take place. Either
the SFL can be treated as an LSP label that was not PHPed and the
additional associated SFL action is taken when the label is
processed. Alternatively, it can be treated as an MPLS Explicit NULL
with associated SFL actions. From the perspective of the measurement
system described in this document the behaviour of the two approaches
is indistinguishable and thus either may be implemented.
4.2.1. Setting TTL and the Traffic Class Bits
The TTL and the Traffic Class considerations described in
Section 4.1.1 apply.
4.3. Aggregation of SFL Actions
There are cases where it is desirable to aggregate an SFL action
against a number of labels. For example, where it is desirable to
have one counter record the number of packets received over a group
of application labels, or where the number of labels used by a single
application is large, and the resultant increase in the number of
allocated labels needed to support the SFL actions may becomes too
large to be viable. In these circumstances it would be necessary to
introduce an additional label in the stack to act as an aggregate
instruction. This is not strictly a synonymous action in that the
SFL is not replacing an existing label, but is somewhat similar to
the single label case shown in Section 4.2, and the same signalling,
management and configuration tools would be applicable.
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+-----------------+
| LSP |
| Label |
| (May be PHPed) |
+-----------------+ +-----------------+
| LSP | | |
| Label | | Aggregate |
| (May be PHPed) | | SFL |
+-----------------+ +-----------------+
| | | |
| Application | | Application |
| Label | | Label |
+-----------------+ <=BoS +-----------------+ <= Bottom of stack
| | | |
| Payload | | Payload |
| | | |
+-----------------+ +-----------------+
"Normal" Label Stack Label Stack with SFL
Figure 3: Aggregate SFL Actions
The Aggregate SFL is shown in the label stack depicted in Figure 3 as
preceding the application label, however the choice of position
before, or after, the application label will be application specific.
In the case described in Section 4.1, by definition the SFL has the
full application context. In this case the positioning will depend
on whether the SFL action needs the full context of the application
to perform its action and whether the complexity of the application
will be increased by finding an SFL following the application label.
5. Equal Cost Multipath Considerations
The introduction of an SFL to an existing flow may cause that flow to
take a different path through the network under conditions of Equal
Cost Multi-path (ECMP). This in turn may invalidate certain uses of
the SFL such as performance measurement applications. Where this is
a problem there are two solutions worthy of consideration:
1. The operator MAY elect to always run with the SFL in place in the
MPLS label stack.
2. The operator can elect to use [RFC6790] Entropy Labels in a
network that fully supports this type of ECMP. If this approach
is adopted, the intervening MPLS network MUST NOT load balance on
any packet field other than the entropy label. Note that this is
stricter than the text in Section 4.3 of [RFC6790].
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6. Privacy Considerations
IETF concerns on pervasive monitoring are described in [RFC7258].
The inclusion of originating and/or flow information in a packet
provides more identity information and hence potentially degrades the
privacy of the communication to an attacker in a position to observe
the added identifier. Whilst the inclusion of the additional
granularity does allow greater insight into the flow characteristics
it does not specifically identify which node originated the packet
unless the attacker can inspect the network at the point of ingress,
or inspection of the control protocol packets. This privacy threat
may be mitigated by encrypting the control protocol packets, by
regularly changing the synonymous labels or by concurrently using a
number of such labels, including the use of a combination of those
methods. Minimizing the scope of the identity indication can be
useful in minimizing the observability of the flow characteristics.
Whenever IPFIX or other DPI technique is used, their relavent privacy
considerations apply.
7. Security Considerations
There are no new security issues associated with the MPLS data plane.
Any control protocol used to request SFLs will need to ensure the
legitimacy of the request, i.e. that the requesting node is
authorized to make that SFL request by the network operator.
8. IANA Considerations
This draft makes no IANA requests.
9. Contributing Authors
Zhenbin Li
Huawei
Email: lizhenbin@huawei.com
10. References
10.1. 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,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, DOI 10.17487/RFC5462, February
2009, <https://www.rfc-editor.org/info/rfc5462>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References
[I-D.bryant-mpls-sfl-control]
Bryant, S., Swallow, G., and S. Sivabalan, "A Simple
Control Protocol for MPLS SFLs", draft-bryant-mpls-sfl-
control-08 (work in progress), June 2020.
[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985,
DOI 10.17487/RFC3985, March 2005,
<https://www.rfc-editor.org/info/rfc3985>.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374,
DOI 10.17487/RFC6374, September 2011,
<https://www.rfc-editor.org/info/rfc6374>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<https://www.rfc-editor.org/info/rfc7011>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>.
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[RFC8321] Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli,
L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
"Alternate-Marking Method for Passive and Hybrid
Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321,
January 2018, <https://www.rfc-editor.org/info/rfc8321>.
[RFC8372] Bryant, S., Pignataro, C., Chen, M., Li, Z., and G.
Mirsky, "MPLS Flow Identification Considerations",
RFC 8372, DOI 10.17487/RFC8372, May 2018,
<https://www.rfc-editor.org/info/rfc8372>.
Authors' Addresses
Stewart Bryant
Futurewei Technologies Inc
Email: sb@stewartbryant.com
Mach Chen
Huawei
Email: mach.chen@huawei.com
George Swallow
Southend Technical Center
Email: swallow.ietf@gmail.com
Siva Sivabalan
Ciena Corporation
Email: ssivabal@ciena.com
Gregory Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
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