MPLS S. Bryant
Internet-Draft G. Swallow
Intended status: Standards Track S. Sivabalan
Expires: January 4, 2016 Cisco Systems
G. Mirsky
Ericsson
M. Chen
Z. Li
Huawei
July 3, 2015
RFC6374 Synonymous Flow Labels
draft-bryant-mpls-synonymous-flow-labels-01
Abstract
[Editor's note - there was a comment that synonymous was not the
right term because synonymous implied a greater degree of
interchangeability than is actually the case (there is only one way
interchangeability). I have looked for other terms, and so far I
have only come up with enhanced and multi-purpose, but they are not
quite right either. I plan to continue with the term unless anyone
has a better idea.]
This document describes a method of providing flow identification
information when making RFC6374 performance measurements. This
allows RFC6374 measurements to be made on multi-point to point LSPs
and allows the measurement of flows within an MPLS construct using
RFC6374.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 4, 2016.
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Copyright Notice
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document authors. All rights reserved.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Synonymous Flow Labels . . . . . . . . . . . . . . . . . . . 4
4. User Service Traffic in the Data Plane . . . . . . . . . . . 5
4.1. Applications Label Present . . . . . . . . . . . . . . . 5
4.1.1. Setting TTL and the Traffic Class Bits . . . . . . . 6
4.2. Single Label Stack . . . . . . . . . . . . . . . . . . . 6
4.2.1. Setting TTL and the Traffic Class Bits . . . . . . . 7
4.3. Aggregation of SFL Actions . . . . . . . . . . . . . . . 7
5. Equal Cost Multipath Considerations . . . . . . . . . . . . . 8
6. RFC6374 Packet Loss Measurement with SFL . . . . . . . . . . 9
6.1. RFC6374 SFL TLV . . . . . . . . . . . . . . . . . . . . . 10
7. The Application of SFL to other PM Types . . . . . . . . . . 12
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
12.1. Normative References . . . . . . . . . . . . . . . . . . 13
12.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
[I-D.bryant-mpls-flow-ident] describes the requirement for
introducing flow identities when using RFC6374 [RFC6374] packet Loss
Measurements (LM). In summary RFC6374 uses the LM packet as the
packet accounting demarcation point. Unfortunately this gives rise
to a number of problems that may lead to significant packet
accounting errors in certain situations. For example:
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1. Where a flow is subjected to Equal Cost Multi-Path (ECMP)
treatment packets can arrive out of order with respect to the LM
packet.
2. Where a flow is subjected to ECMP treatment, packets can arrive
at different hardware interfaces, thus requiring reception of an
LM packet on one interface to trigger a packet accounting action
on a different interface which may not be co-located with it.
This is a difficult technical problem to address with the
required degree of accuracy.
3. Even where there is no ECMP (for example on RSVP-TE, MPLS-TP LSPs
and PWs) local processing may be distributed over a number of
processor cores, leading to synchronization problems.
4. Link aggregation techniques may also lead to synchronization
issues.
5. Some forwarder implementations have a long pipeline between
processing a packet and incrementing the associated counter again
leading to synchronization difficulties.
An approach to mitigating these synchronization issue is described in
[I-D.tempia-ippm-p3m] and
[I-D.chen-ippm-coloring-based-ipfpm-framework] in which packets are
batched by the sender and each batch is marked in some way such that
adjacent batches can be easily recognized by the receiver.
An additional problem arises where the LSP is a multi-point to point
LSP, since MPLS does not include a source address in the packet.
Network management operations require the measurement of packet loss
between a source and destination. It is thus necessary to introduce
some source specific information into the packet to identify packet
batches from a specific source.
This document describes a method of accomplishing this by using a
technique called Synonymous Flow Labels (SFL) (see (Section 3)) in
which labels which mimic the behaviour of other labels provide the
packet batch identifiers and enable the per batch packet accounting.
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
[RFC2119].
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3. Synonymous Flow Labels
An SFL is defined to be a label that causes exactly the same
behaviour at the egress Label Switching Router (LSR) as the label it
replaces, except that it also causes an additional agreed action to
take place on the packet. There are many possible additional actions
such as the measurement of the number of received packets in a flow,
triggering IPFIX inspection, triggering other types of Deep Packet
Inspection, or identification of the packet source. In, for example,
a Performance Monitoring (PM) application, the agreed action would 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.
Consider an MPLS application such as a pseudowire (PW), and consider
that it is desired to use the approach specified in this document to
make a packet loss measurement. By some method outside the scope of
this text, two labels, synonymous with the PW labels are obtained
from the egress terminating provider edge (T-PE). By alternating
between these SLs and using them in place of the PW label, the PW
packets may be batched for counting without any impact on the PW
forwarding behaviour (note that strictly only one SL is needed in
this application, but that is an optimization that is a matter for
the implementor).
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 SLs 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 co-ordinating with the
destination. Each ingress 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. In
this case introducing an SL that was synonymous with the LSP label
would 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. In both of these cases the label has the
additional semantics of the SL.
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Note that to achieve the goals set out in Section 1 SLs 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. Applications label present
2. Single label stack
4.1. Applications Label Present
Figure 1 shows the case in which both an LSP label and an application
label is present in the MPLS label stack. Uninstrumented traffic
runs over the "normal" stack, and instrumented flows run over the SFL
stack with the SFL used to indicate the packet batch.
+-----------------+ +-----------------+
| | | |
| LSP | | LSP | <May be PHPed
| Label | | Label |
+-----------------+ +-----------------+
| | | |
| Application | | Synonymous Flow |
| Label | | Label |
+-----------------+ +-----------------+ <= 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
At the egress LSR the LSP label is popped (if present). Then the SFL
is processed in exactly the same way as the corresponding application
label would have been processed. Where the SFL is being used to
support RFC6374 packet loss measurements, as an additional operation,
the total number of packets received with this particular SFL is
recorded.
Where the number of labels used by a single application is large, and
the increase in the number of allocated labels needed to support the
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SFL actions consequently becomes too large to be viable, it may be
necessary to introduce an additional label in the stack to act as an
aggregate instruction. This situation will be considered in a future
version of this document.
4.1.1. Setting TTL and the Traffic Class Bits
To be provided in a future version of this draft.
4.2. Single Label Stack
Figure 2 shows the case in which only an LSP label is present in the
MPLS label stack. Uninstrumented traffic runs over the "normal"
stack and instrumented 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 LSR to first push the SFL and then to push the LSP
label.
+-----------------+
| |
| LSP | <= May be PHPed
| Label |
+-----------------+ +-----------------+
| | | | <= Synonymous with
| LSP | | Synonymous Flow | Explicit NULL
| Label | | Label |
+-----------------+ +-----------------+ <= 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 LSR it is necessary to consider two cases:
1. Where the LSP label is still present
2. Where the LSP label is penultimate hop popped
If the LSP label is present, it 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
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discarded. In this respect the processing of the SFL is synonymous
with an 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 explicit NULL with
associated SFL actions. From the perspective of the measurement
system described in this document the behaviour of two approaches are
indistinguishable and thus either may be implemented.
4.2.1. Setting TTL and the Traffic Class Bits
To be provided in a future version of this draft.
4.3. Aggregation of SFL Actions
There are cases where it is desirable to agregate 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 consequently the increase in the number of
allocated labels needed to support the SFL actions consequently
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 a 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 | < May be PHPed
| Lable |
+-----------------+ +-----------------+
| | | |
| LSP | | Agregate |
| Label | | SFL |
+-----------------+ +-----------------+
| | | |
| Application | | Application |
| Label | | Label |
+-----------------+ +-----------------+ <= 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
preceeding 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.
This third SFL case requires further though by the authors and this
section will be updated in a future version of this draft to reflect
those thoughts.
5. Equal Cost Multipath Considerations
The introduction to an SFL to and existing may cause that flow to
take a different path through the network under conditions of Equal
Cost Multipath (ECMP). This is turn may invalidate the certain uses
of the SFL such as PM. Where this is a problem there are two
solutions worthy of consideration:
1. The operator can elect to always run with the SFL in place in the
MPLS label stack.
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2. The operator can elect to use [RFC6790] Entropy Labels which, in
a network that fully supports this type of ECMP, results in the
ECMP decision being independent of the value of the other labels
in the label stack.
6. RFC6374 Packet Loss Measurement with SFL
The packet format of an RFC6374 Query message using SFLs is shown in
Figure 4.
+-------------------------------+
| |
| LSP |
| Label |
+-------------------------------+
| |
| Synonymous Flow |
| Label |
+-------------------------------+
| |
| |
| RFC6374 Measurement Message |
| |
| +-------------------------+ |
| | | |
| | RFC6374 Fixed | |
| | Header | |
| | | |
| +-------------------------+ |
| | | |
| | Optional SFL TLV | |
| | | |
| +-------------------------+ |
| | | |
| | Optional Return | |
| | Information | |
| | | |
| +-------------------------+ |
| |
+-------------------------------+
Figure 4: RFC6734 Query Packet with SFL
The MPLS label stack is exactly the same as that used for the user
data service packets being instrumented (see Section 4). The RFC6374
measurement message consists of the three components, the RFC6374
fixed header as specified in [RFC6374] carried over the ACH channel
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type specified the type of measurement being made (currently: loss,
delay or loss and delay) as specified in RFC6374.
Two optional TLVs MAY also be carried if needed. The first is the
SFL TLV specified in Section 6.1. This is used to provide the
implementation with a reminder of the SFL that was used to carry the
RFC6374 message. This is needed because a number of MPLS
implementations do not provide the MPLS label stack to the MPLS OAM
handler. This TLV is required if RFC6374 messages are sent over UDP
(draft-bryant-mpls-RFC6374-over-udp). This TLV MUST be included
unless, by some method outside the scope of this document, it is
known that this information is not needed by the RFC6374 Responder.
The second set of information that may be needed is the return
information that allows the responder send the RFC6374 response to
the Querier. This is not needed if the response is requested in-band
and the MPLS construct being measured is a point to point LSP, but
otherwise MUST be carried. The return address TLV is defined in
RFC6378 and the optional UDP Return Object is defined in
[I-D.ietf-mpls-rfc6374-udp-return-path].
6.1. RFC6374 SFL TLV
[Editor's Note we need to review the following in the light of
further thoughts on the associated signaling protocol(s). I am
fairly confident that we need all the fields other than SFL Batch and
SFL Index. The Index is useful in order to map between the label and
information associated with the FEC. The batch is part of the
lifetime management process]
The required RFC6374 SFL TLV is shown in Figure 5. This contains the
SFL that was carried in the label stack, the FEC that was used to
allocate the SFL and the index into the batch of SLs that were
allocated for the FEC that corresponds to this SFL.
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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 | Length |MBZ| SFL Batch | SFL Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SFL | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC |
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: SFL TLV
Where:
Type Type is set to Synonymous Flow Label (SFL-TLV).
Length The length of the TLV as specified in [RFC6374].
MBZ MUST be sent as zero and ignored on receive.
SFL Batch The SFL batch that this SFL was allocated as part of
(see draft-bryant-mpls-sfl-control)
SPL Index The index into the list of SFLs that were assigned
against the FEC that corresponds to the SFL.
SFL The SFL used to deliver this packet. This is an MPLS
label which is a component of a label stack entry as
defined in Section 2.1 of [RFC3032].
Reserved MUST be sent as zero and ignored on receive.
FEC The Forwarding Equivalence Class that was used to
request this SFL. This is encoded as per
Section 3.4.1 of
This information is needed to allow for operation with hardware that
discards the MPLS label stack before passing the remainder of the
stack to the OAM handler. By providing both the SFL and the FEC plus
index into the array of allocated SFLs a number of implementation
types are supported.
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7. The Application of SFL to other PM Types
SFL can be used to enable other types of PM in addition to loss.
Delay, Delay Variation and Throughput may be calculated based on
measurement results collected through Loss and Delay Measurement test
sessions. Further details will be provided in a future version of
this draft.
8. Privacy Considerations
The inclusion of originating and/or flow information in a packet
provides more identity information and hence potentially degrades the
privacy of the communication. 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
other than by inspection of 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, regularly
changing the synonymous labels and by concurrently using a number of
such labels.
9. Security Considerations
The issue noted in Section 8 is a security consideration. There are
no other new security issues associated with the MPLS dataplane. Any
control protocol used to request SFLs will need to ensure the
legitimacy of the request.
10. IANA Considerations
IANA is request to allocate a new TLV from the 0-127 range on the
MPLS Loss/Delay Measurement TLV Object Registry:
Type Description Reference
---- --------------------------------- ---------
TBD Synonymous Flow Label This
A value of 4 is recommended.
11. Acknowledgements
TBD
12. References
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12.1. Normative References
[I-D.ietf-mpls-rfc6374-udp-return-path]
Bryant, S., Sivabalan, S., and S. Soni, "RFC6374 UDP
Return Path", draft-ietf-mpls-rfc6374-udp-return-path-03
(work in progress), April 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001.
12.2. Informative References
[I-D.bryant-mpls-flow-ident]
Bryant, S., Pignataro, C., Chen, M., Li, Z., and G.
Mirsky, "MPLS Flow Identification", draft-bryant-mpls-
flow-ident-01 (work in progress), March 2015.
[I-D.chen-ippm-coloring-based-ipfpm-framework]
Chen, M., Zheng, L., Mirsky, G., and G. Fioccola, "IP Flow
Performance Measurement Framework", draft-chen-ippm-
coloring-based-ipfpm-framework-03 (work in progress),
February 2015.
[I-D.tempia-ippm-p3m]
Capello, A., Cociglio, M., Fioccola, G., Castaldelli, L.,
and A. Bonda, "A packet based method for passive
performance monitoring", draft-tempia-ippm-p3m-00 (work in
progress), March 2015.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374, September 2011.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, November 2012.
Authors' Addresses
Stewart Bryant
Cisco Systems
Email: stbryant@cisco.com
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George Swallow
Cisco Systems
Email: swallow@cisco.com
Siva Sivabalan
Cisco Systems
Email: msiva@cisco.com
Greg Mirsky
Ericsson
Email: gregory.mirsky@ericsson.com
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com
Zhenbin(Robin) Li
Huawei
Email: lizhenbin@huawei.com
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