RFC6374 Synonymous Flow Labels
draft-ietf-mpls-rfc6374-sfl-10
| Document | Type | Active Internet-Draft (mpls WG) | ||
|---|---|---|---|---|
| Authors | Stewart Bryant , George Swallow , Mach Chen , Giuseppe Fioccola , Greg Mirsky | |||
| Last updated | 2021-03-26 (latest revision 2021-03-05) | |||
| Replaces | draft-bryant-mpls-rfc6374-sfl | |||
| Stream | Internet Engineering Task Force (IETF) | |||
| Intended RFC status | Proposed Standard | |||
| Formats | plain text xml pdf htmlized bibtex | |||
| Reviews | ||||
| Stream | WG state | Submitted to IESG for Publication | ||
| Document shepherd | Loa Andersson | |||
| Shepherd write-up | Show (last changed 2020-12-09) | |||
| IESG | IESG state | RFC Ed Queue | ||
| Action Holders |
(None)
|
|||
| Consensus Boilerplate | Yes | |||
| Telechat date | ||||
| Responsible AD | Deborah Brungard | |||
| Send notices to | Loa Andersson <loa@pi.nu>, mpls-chairs@ietf.org, draft-ietf-mpls-rfc6374-sfl@ietf.org | |||
| IANA | IANA review state | Version Changed - Review Needed | ||
| IANA action state | RFC-Ed-Ack | |||
| RFC Editor | RFC Editor state | MISSREF | ||
| Details | ||||
MPLS Working Group S. Bryant (Ed)
Internet-Draft Futurewei Technologies Inc.
Intended status: Standards Track G. Swallow
Expires: September 6, 2021 Southend Technical Center
M. Chen
Huawei
G. Fioccola
Huawei Technologies
G. Mirsky
ZTE Corp.
March 05, 2021
RFC6374 Synonymous Flow Labels
draft-ietf-mpls-rfc6374-sfl-10
Abstract
RFC 6374 describes methods of making loss and delay measurements on
Label Switched Paths (LSPs) primarily as used in MPLS Transport
Profile (MPLS-TP) networks. This document describes a method of
extending RFC 6374 performance measurements from flows carried over
MPLS-TP to flows carried over generic MPLS LSPs. In particular, it
extends the technique to allow loss and delay measurements to be made
on multi-point to point LSPs and introduces some additional
techniques to allow more sophisticated measurements to be made in
both MPLS-TP and generic MPLS networks.
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 https://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 September 6, 2021.
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Copyright Notice
Copyright (c) 2021 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
(https://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. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. RFC6374 Packet Loss Measurement with SFL . . . . . . . . . . 4
4. RFC6374 Single Packet Delay Measurement . . . . . . . . . . . 4
5. Data Service Packet Delay Measurement . . . . . . . . . . . . 5
6. Some Simplifying Rules . . . . . . . . . . . . . . . . . . . 6
7. Multiple Packet Delay Characteristics . . . . . . . . . . . . 7
7.1. Method 1: Time Buckets . . . . . . . . . . . . . . . . . 7
7.2. Method 2 Classic Standard Deviation . . . . . . . . . . . 9
7.2.1. Multi-Packet Delay Measurement Message Format . . . . 10
7.3. Per Packet Delay Measurement . . . . . . . . . . . . . . 11
7.4. Average Delay . . . . . . . . . . . . . . . . . . . . . . 11
8. Sampled Measurement . . . . . . . . . . . . . . . . . . . . . 13
9. Carrying RFC6374 Packets over an LSP using an SFL . . . . . . 13
9.1. RFC6374 SFL TLV . . . . . . . . . . . . . . . . . . . . . 15
10. RFC6374 Combined Loss-Delay Measurement . . . . . . . . . . . 16
11. Privacy Considerations . . . . . . . . . . . . . . . . . . . 17
12. Security Considerations . . . . . . . . . . . . . . . . . . . 17
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
13.1. Allocation of MPLS Generalized Associated Channel
(G-ACh) Types . . . . . . . . . . . . . . . . . . . . . 17
13.2. Allocation of MPLS Loss/Delay TLV Object . . . . . . . . 18
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
15. Contributing Authors . . . . . . . . . . . . . . . . . . . . 18
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
16.1. Normative References . . . . . . . . . . . . . . . . . . 18
16.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
[RFC6374] was originally designed for use as an Operations,
Administration, and Maintenance (OAM) protocol for use with MPLS
Transport Profile (MPLS-TP) [RFC5921] LSPs. MPLS-TP only supports
point-to-point and point-to-multi-point LSPs. This document
describes how to use RFC6374 in the generic MPLS case, and also
introduces a number of more sophisticated measurements of
applicability to both cases.
[RFC8372] describes the requirement for introducing flow identities
when using RFC6374 [RFC6374] packet Loss Measurements (LM). In
summary RFC6374 uses the loss-measurement (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:
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 pseudowires(PWs)) local processing may be distributed over a
number of processor cores, leading to synchronization problems.
4. Link aggregation techniques [RFC7190] 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
[RFC8321] 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
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some source specific information into the packet to identify packet
batches from a specific source.
[RFC8957] describes a method of encoding per flow instructions in an
MPLS label stack using a technique called Synonymous Flow Labels
(SFL) in which labels which mimic the behavior of other labels
provide the packet batch identifiers and enable the per batch packet
accounting. This memo specifies how SFLs are used to perform RFC6374
packet loss and RFC6374 delay measurements.
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
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. RFC6374 Packet Loss Measurement with SFL
The data service packets of the flow being instrumented are grouped
into batches, and all the packets within a batch are marked with the
SFL [RFC8372] corresponding to that batch. The sender counts the
number of packets in the batch. When the batch has completed and the
sender is confident that all of the packets in that batch will have
been received, the sender issues an RFC6374 Query message to
determine the number actually received and hence the number of
packets lost. The RFC6374 Query message is sent using the same SFL
as the corresponding batch of data service packets. The format of
the Query and Response packets is described in Section 9.
4. RFC6374 Single Packet Delay Measurement
RFC6374 describes how to measure the packet delay by measuring the
transit time of an RFC6374 packet over an LSP. Such a packet may not
need to be carried over an SFL since the delay over a particular LSP
should be a function of the Traffic Class (TC) bits.
However, where SFLs are being used to monitor packet loss or where
label inferred scheduling is used [RFC3270] then the SFL would be
REQUIRED to ensure that the RFC6374 packet which was being used as a
proxy for a data service packet experienced a representative delay.
The format of an RFC6374 packet carried over the LSP using an SFL is
shown in Section 9.
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5. Data Service Packet Delay Measurement
Where it is desired to more thoroughly instrument a packet flow and
to determine the delay of a number of packets it is undesirable to
send a large number of RFC6374 packets acting as a proxy data service
packets (see Section 4). A method of directly measuring the delay
characteristics of a batch of packets is therefore needed.
Given the long intervals over which it is necessary to measure packet
loss, it is not necessarily the case that the batch times for the two
measurement types would be identical. Thus, we use a technique that
permits the two measurements are made concurrently and yet relatively
independent from each other. The notion that they are relatively
independent arises from the potential for the two batches to overlap
in time, in which case either the delay batch time will need to be
cut short or the loss time will need to be extended to allow correct
reconciliation of the various counters.
The problem is illustrated in Figure 1 below:
(1) AAAAAAAAAABBBBBBBBBBAAAAAAAAAABBBBBBBBBB
SFL Marking of a packet batch for loss measurement
(2) AADDDDAAAABBBBBBBBBBAAAAAAAAAABBBBBBBBBB
SFL Marking of a subset of the packets for delay
(3) AAAAAAAADDDDBBBBBBBBAAAAAAAAAABBBBBBBBBB
SFL Marking of a subset of the packets across a
packet loss measurement boundary
(4) AACDCDCDAABBBBBBBBBBAAAAAAAAAABBBBBBBBBB
The case of multiple delay measurements within
a packet loss measurement
A & B are packets where loss is being measured
C & D are pacekts where loss and delay is being measured
Figure 1: RFC6734 Query Packet with SFL
In case 1 of Figure 1 we show the case where loss measurement alone
is being carried out on the flow under analysis. For illustrative
purposes consider that 10 packets are used in each flow in the time
interval being analyzed.
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Now consider case 2 of Figure 1 where a small batch of packets need
to be analyzed for delay. These are marked with a different SFL type
indicating that they are to be monitored for both loss and delay.
The SFL=A indicates loss batch A, SFL=D indicates a batch of packets
that are to be instrumented for delay, but SFL D is synonymous with
SFL A, which in turn is synonymous with the underlying Forwarding
Equivalence Class (FEC). Thus, a packet marked D will be accumulated
into the A loss batch, into the delay statistics and will be
forwarded as normal. Whether the packet is actually counted twice
(for loss and delay) or whether the two counters are reconciled
during reporting is a local matter.
Now consider case 3 of Figure 1 where a small batch of packets are
marked for delay across a loss batch boundary. These packets need to
be considered as part of batch A or a part of batch B, and any
RFC6374 Query needs to take place after all the packets A or D
(whichever option is chosen) have arrived at the receiving LSR.
Now consider case 4 of Figure 1. Here we have a case where it is
required to take a number of delay measurements within a batch of
packets that we are measuring for loss. To do this we need two SFLs
for delay (C and D) and alternate between them (on a delay batch by
delay batch basis) for the purposes of measuring the delay
characteristics of the different batches of packets.
6. Some Simplifying Rules
It is possible to construct a large set of overlapping measurement
types, in terms of loss, delay, loss and delay and batch overlap. If
we allow all combinations of cases, this leads to configuration,
testing and implementation complexity and hence increased costs. The
following simplifying rules represent the default case:
1. Any system that needs to measure delay MUST be able to measure
loss.
2. Any system that is to measure delay MUST be configured to measure
loss. Whether the loss statistics are collected or not is a
local matter.
3. A delay measurement MAY start at any point during a loss
measurement batch, subject to rule 4.
4. A delay measurement interval MUST be short enough that it will
complete before the enclosing loss batch completes.
5. The duration of a second delay (D in Figure 1 batch must be such
that all packets from the packets belonging to a first delay
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batch (C in Figure 1)will have been received before the second
delay batch completes. This condition is satisfied when the time
to send a batch is long compared to the network propagation time,
and is a parameter that can be established by the network
operator.
Given that the sender controls both the start and duration of a loss
and a delay packet batch, these rules are readily implemented in the
control plane.
7. Multiple Packet Delay Characteristics
A number of methods are described which add to the set of
measurements originally specified in [RFC6374]. Each of these
methods has different characteristics and different processing
demands on the packet forwarder. The choice of method will depend on
the type of diagnostic that the operator seeks.
Three Methods are discussed:
1. Time Buckets
2. Classic Standard Deviation
3. Average Delay
7.1. Method 1: Time Buckets
In this method the receiving LSR measures the inter-packet gap,
classifies the delay into a number of delay buckets and records the
number of packets in each bucket. As an example, if the operator
were concerned about packets with a delay of up to 1us, 2us, 4us,
8us, and over 8us then there would be five buckets and packets that
arrived up to 1us would cause the 1us bucket counter to increase,
between 1us and 2us the 2us bucket counter would increase etc. In
practice it might be better in terms of processing and potential
parallelism if, when a packet had a delay relative to its predecessor
of 2us, then both the up to 1us and the 2us counter were incremented,
and any more detailed information was calculated in the analytics
system.
This method allows the operator to see more structure in the jitter
characteristics than simply measuring the average jitter, and avoids
the complication of needing to perform a per packet multiply, but
will probably need the time intervals between buckets to be
programmable by the operator.
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The packet format of a Time Bucket Jitter Measurement Message is
shown below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Flags | Control Code | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QTF | RTF | RPTF | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session Identifier | DS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of | Reserved 1 |
| Buckets | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interval in 10ns units |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number pkts in Bucket |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ TLV Block ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Time Bucket Jitter Measurement Message Format
The Version, Flags, Control Code, Message Length, QTF, RTF, RPTF,
Session Identifier, Reserved and DS Fields are as defined in section
3.2 of RFC6374. The remaining fields, which are unsigned integers,
are as follows:
o Number of Buckets in the measurement
o Reserved 1 must be sent as zero and ignored on receipt
o Interval in 10ns units is the inter-packet interval for
this bucket
o Number Pkts in Bucket is the number of packets found in
this bucket.
There will be a number of Interval/Number pairs depending on the
number of buckets being specified by the Querier. If an RFC6374
message is being used to configure the buckets, (i.e. the responder
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is creating or modifying the buckets according to the intervals in
the Query message), then the Responder MUST respond with 0 packets in
each bucket until it has been configured for a full measurement
period. This indicates that it was configured at the time of the
last response message, and thus the response is valid for the whole
interval. As per the [RFC6374] convention the Number of pkts in
Bucket fields are included in the Query message and set to zero.
Out of band configuration is permitted by this mode of operation.
Note this is a departure from the normal fixed format used in
RFC6374.
The time bucket jitter measurement message is carried over an LSP in
the way described in [RFC6374] and over an LSP with an SFL as
described in Section 9.
7.2. Method 2 Classic Standard Deviation
In this method, provision is made for reporting the following delay
characteristics:
1. Number of packets in the batch (n).
2. Sum of delays in a batch (S)
3. Maximum Delay.
4. Minimum Delay.
5. Sum of squares of Inter-packet delay (SS).
Characteristics 1 and 2 give the mean delay. Measuring the delay of
each pair in the batch is discussed in Section 7.3.
Characteristics 3 and 4 give the outliers.
Characteristics 1, 2 and 5 can be used to calculate the variance of
the inter-packet gap and hence the standard deviation giving a view
of the distribution of packet delays and hence the jitter. The
equation for the variance (var) is given by:
var = (SS - S*S/n)/(n-1)
There is some concern over the use of this algorithm for measuring
variance, because SS and S*S/n can be similar numbers, particularly
where variance is low. However the method commends it self by not
requiring a division in the hardware.
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7.2.1. Multi-Packet Delay Measurement Message Format
The packet format of a Multi-Packet Delay Measurement Message is
shown below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Flags | Control Code | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QTF | RTF | RPTF | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session Identifier | DS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Packets |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sum of Delays for Batch |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Minimum Delay |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Delay |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sum of squares of Inter-packet delay |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ TLV Block ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Multi-packet Delay Measurement Message Format
The Version, Flags, Control Code, Message Length, QTF, RTF, RPTF,
Session Identifier, Reserved and DS Fields are as defined in section
3.2 of RFC6374. The remaining fields are as follows:
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o Number of Packets is the number of packets in this batch
o Sum of Delays for Batch is the duration of the batch in the
time measurement format specified in the RTF field.
o Minimum Delay is the minimum inter-packet gap observed during
the batch in the time format specified in the RTF field.
o Maximum Delay is the maximum inter-packet gap observed during
the batch in the time format specified in the RTF field.
The multi-packet delay measurement message is carried over an LSP in
the way described in [RFC6374] and over an LSP with an SFL as
described in Section 9.
7.3. Per Packet Delay Measurement
If detailed packet delay measurement is required then it might be
possible to record the inter-packet gap for each packet pair. In
other than exception cases of slow flows or small batch sizes, this
would create a large (per packet) demand on storage in the
instrumentation system, a large bandwidth to such a storage system
and large bandwidth to the analytics system. Such a measurement
technique is outside the scope of this document.
7.4. Average Delay
Introduced in [RFC8321] is the concept of a one way delay measurement
in which the average time of arrival of a set of packets is measured.
In this approach the packet is time-stamped at arrival and the
Responder returns the sum of the time-stamps and the number of times-
tamps. From this the analytics engine can determine the mean delay.
An alternative model is that the Responder returns the time stamp of
the first and last packet and the number of packets. This later
method has the advantage of allowing the average delay to be
determined at a number of points along the packet path and allowing
the components of the delay to be characterized. Unless specifically
configured otherwise, the responder may return either or both types
of response and the analytics engine should process the response
appropriately.
The packet format of an Average Delay Measurement Message is shown
below:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Flags | Control Code | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QTF | RTF | RPTF | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session Identifier | DS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Packets |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time of First Packet |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time of Last Packet |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sum of Timestamps of Batch |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ TLV Block ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Average Delay Measurement Message Format
The Version, Flags, Control Code, Message Length, QTF, RTF, RPTF,
Session Identifier, and DS Fields are as defined in section 3.2 of
RFC6374. The remaining fields are as follows:
o Number of Packets is the number of packets in this batch.
o Time of First Packet is the time of arrival of the first
packet in the batch.
o Time of Last Packet is the time of arrival of the last
packet in the batch.
o Sum of Timestamps of Batch.
The average delay measurement message is carried over an LSP in the
way described in [RFC6374] and over an LSP with an SFL as described
in Section 9. As is the convention with RFC6374, the Query message
contains placeholders for the Response message. The placeholders are
sent as zero.
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8. Sampled Measurement
In the discussion so far it has been assumed that we would measure
the delay characteristics of every packet in a delay measurement
interval defined by an SFL of constant color. In [RFC8321] the
concept of a sampled measurement is considered. That is the
Responder only measures a packet at the start of a group of packets
being marked for delay measurement by a particular color, rather than
every packet in the marked batch. A measurement interval is not
defined by the duration of a marked batch of packets but the interval
between a pair of RFC6374 packets taking a readout of the delay
characteristic. This approach has the advantage that the measurement
is not impacted by ECMP effects.
This sampled approach may be used if supported by the Responder and
configured by the opertor.
9. Carrying RFC6374 Packets over an LSP using an SFL
We illustrate the packet format of an RFC6374 Query message using
SFLs for the case of an MPLS direct loss measurement in Figure 5.
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+-------------------------------+
| |
| LSP |
| Label |
+-------------------------------+
| |
| Synonymous Flow |
| Label |
+-------------------------------+
| |
| GAL |
| |
+-------------------------------+
| |
| ACH Type = 0xA |
| |
+-------------------------------+
| |
| RFC6374 Measurement Message |
| |
| +-------------------------+ |
| | | |
| | Fixed-format | |
| | portion of msg | |
| | | |
| +-------------------------+ |
| | | |
| | Optional SFL TLV | |
| | | |
| +-------------------------+ |
| | | |
| | Optional Return | |
| | Information | |
| | | |
| +-------------------------+ |
| |
+-------------------------------+
Figure 5: RFC6734 Query Packet with SFL
The MPLS label stack is exactly the same as that used for the user
data service packets being instrumented except for the inclusion of
the Generic Associated Channel Label (GAL) [RFC5586] to allow the
receiver to distinguish between normal data packets and OAM packets.
Since the packet loss measurements are being made on the data service
packets, an RFC6374 direct loss measurement is being made, and which
is indicated by the type field in the ACH (Type = 0x000A).
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The RFC6374 measurement message consists of the three components, the
RFC6374 fixed-format portion of the message as specified in [RFC6374]
carried over the ACH channel 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 9.1. 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
[RFC7876]. 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
[RFC6374] and the optional UDP Return Object is defined in [RFC7876].
Where a measurement other than an MPLS direct loss measurement is to
be made, the appropriate RFC6374 measurement message is used (for
example, one of the new types defined in this document) and this is
indicated to the receiver by the use of the corresponding ACH type.
9.1. RFC6374 SFL TLV
The RFC6374 SFL TLV is shown in Figure 6. 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.
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 6: SFL TLV
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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 [I-D.bryant-mpls-sfl-control]
SPL Index The index into the list of SFLs that were assigned
against the FEC that corresponds to the SFL.
Multiple SFLs can be assigned to a FEC each
with different actions. This index is an optional
convenience for use in mapping between the TLV
and the associated data structures in the LSRs.
The use of this feature is agreed between the
two parties during configuration. It is not required,
but is a convenience for the receiver if both parties
support the facility,
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 [RFC5036]
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.
10. RFC6374 Combined Loss-Delay Measurement
This mode of operation is not currently supported by this
specification.
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11. 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.
12. Security Considerations
The security considerations documented in [RFC6374] and [RFC8372]
(which in turn calls up [RFC7258] and [RFC5920]) are applicable to
this protocol.
The issue noted in Section 11 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.
An attacker that manages to corrupt the RFC6374 SFL TLV Section 9.1
could disrupt the measurements in a way that the RFC6374 responder is
unable to detect. However, the network opertator is likely to notice
the anomalous network performance measurements, and in any case
normal MPLS network security proceedures make this type of attack
extremely unlikley.
13. IANA Considerations
13.1. Allocation of MPLS Generalized Associated Channel (G-ACh) Types
As per the IANA considerations in [RFC5586] updated by [RFC7026] and
[RFC7214], IANA is requested to allocate the following codeponts in
the "MPLS Generalized Associated Channel (G-ACh) Type" registry, in
the "Generic Associated Channel (G-ACh) Parameters" name space:
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Value Description Reference
----- --------------------------------- -----------
TBD RFC6374 Time Bucket Jitter Measurement This
TBD RFC6374 Multi-Packet Delay This
Measurement
TBD RFC6374 Average Delay Measurement This
13.2. Allocation of MPLS Loss/Delay TLV Object
IANA is requested to allocate a new TLV from the 0-127 range of the
MPLS Loss/Delay Measurement TLV Object Registry in the "Generic
Associated Channel (G-ACh) Parameters" namespace:
Type Description Reference
---- --------------------------------- ---------
TBD Synonymous Flow Label This
A value of 4 is recommended.
RFC Editor please delete this para
[RFC3032][I-D.bryant-mpls-sfl-control][RFC5036]
14. Acknowledgments
The authors thank Benjamin Kaduk and Elwyn Davies for their thorough
and thoughtful review of this document.
15. Contributing Authors
Zhenbin Li
Huawei
Email: lizhenbin@huawei.com
Siva Sivabalan
Ciena Corporation
Email: ssivabal@ciena.com
16. References
16.1. Normative 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-09 (work in progress), December 2020.
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[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>.
[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>.
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
October 2007, <https://www.rfc-editor.org/info/rfc5036>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/info/rfc5586>.
[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>.
[RFC7026] Farrel, A. and S. Bryant, "Retiring TLVs from the
Associated Channel Header of the MPLS Generic Associated
Channel", RFC 7026, DOI 10.17487/RFC7026, September 2013,
<https://www.rfc-editor.org/info/rfc7026>.
[RFC7214] Andersson, L. and C. Pignataro, "Moving Generic Associated
Channel (G-ACh) IANA Registries to a New Registry",
RFC 7214, DOI 10.17487/RFC7214, May 2014,
<https://www.rfc-editor.org/info/rfc7214>.
[RFC7876] Bryant, S., Sivabalan, S., and S. Soni, "UDP Return Path
for Packet Loss and Delay Measurement for MPLS Networks",
RFC 7876, DOI 10.17487/RFC7876, July 2016,
<https://www.rfc-editor.org/info/rfc7876>.
[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>.
[RFC8957] Bryant, S., Chen, M., Swallow, G., Sivabalan, S., and G.
Mirsky, "Synonymous Flow Label Framework", RFC 8957,
DOI 10.17487/RFC8957, January 2021,
<https://www.rfc-editor.org/info/rfc8957>.
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16.2. Informative References
[RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-
Protocol Label Switching (MPLS) Support of Differentiated
Services", RFC 3270, DOI 10.17487/RFC3270, May 2002,
<https://www.rfc-editor.org/info/rfc3270>.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
<https://www.rfc-editor.org/info/rfc5920>.
[RFC5921] Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
L., and L. Berger, "A Framework for MPLS in Transport
Networks", RFC 5921, DOI 10.17487/RFC5921, July 2010,
<https://www.rfc-editor.org/info/rfc5921>.
[RFC7190] Villamizar, C., "Use of Multipath with MPLS and MPLS
Transport Profile (MPLS-TP)", RFC 7190,
DOI 10.17487/RFC7190, March 2014,
<https://www.rfc-editor.org/info/rfc7190>.
[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>.
[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
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George Swallow
Southend Technical Center
Email: swallow.ietf@gmail.com
Mach Chen
Huawei
Email: mach.chen@huawei.com
Giuseppe Fioccola
Huawei Technologies
Email: giuseppe.fioccola@huawei.com
Gregory Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
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