Internet DRAFT - draft-browne-sfc-nsh-kpi-stamp
draft-browne-sfc-nsh-kpi-stamp
Network Working Group R. Browne
Internet Draft A. Chilikin
Intended status: Informational Intel
Expires: August 2019 T. Mizrahi
Huawei Network.IO Innovation Lab
February 25, 2019
A Key Performance Indicators (KPI)
Stamping for the Network Service Header (NSH)
draft-browne-sfc-nsh-kpi-stamp-07
Abstract
This document describes a method of carrying Key Performance
Indicators (KPIs) using the Network Service Header (NSH). This method
may be used, for example, to monitor latency and QoS marking to
identify problems on some links or service functions.
Status of this Memo
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document authors. All rights reserved.
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Table of Contents
1. Introduction ................................................ 2
2. Terminology ................................................. 3
2.1. Requirement Language ................................... 3
2.2. Definition of Terms .................................... 3
2.2.1. Terms Defined in this Document .................... 4
2.3. Abbreviations .......................................... 4
3. NSH KPI Stamping: An Overview ............................... 6
3.1. Prerequisites .......................................... 7
3.2. Operation ............................................. 10
3.2.1. Flow Selection ................................... 10
3.2.2. SCP Interface .................................... 10
3.3. Performance Considerations ............................ 11
4. NSH KPI-stamping Encapsulation ............................. 12
4.1. KPI-stamping Extended Encapsulation ................... 13
4.1.1. NSH Timestamping Encapsulation (Extended Mode) ... 15
4.1.2. NSH QoS-stamping Encapsulation (Extended Mode) ... 17
4.2. KPI-stamping Encapsulation (Detection Mode) ........... 20
5. Hybrid Models .............................................. 22
5.1. Targeted VNF Stamp .................................... 23
6. Fragmentation Considerations ............................... 23
7. Security Considerations .................................... 24
8. IANA Considerations ........................................ 25
9. Contributors ............................................... 25
10. Acknowledgments ........................................... 25
11. References ................................................ 25
11.1. Normative References ................................. 25
11.2. Informative References ............................... 26
1. Introduction
Network Service Header (NSH), as defined by [RFC8300], specifies a
method for steering the traffic among an ordered set of Service
Functions (SFs) using an extensible service header. This allows for
flexibility and programmability in the forwarding plane to invoke the
appropriate SFs for specific flows.
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NSH promises a compelling vista of operational flexibility. However,
many service providers are concerned about service and configuration
visibility. This concern increases when considering that many service
providers wish to run their networks seamlessly in 'hybrid' mode,
whereby they wish to mix physical and virtual SFs and run services
seamlessly between the two domains.
This document describes generic methods to monitor and debug service
function chains in terms of latency and QoS marking of the flows
within a service function chain. This is refered to detection mode
and extended mode and explained in section 4.
The method described in the document is compliant with hybrid
architectures in which Virtual Network Functions (VNFs) and Physical
Network Functions (PNFs) are freely mixed in the service function
chain. This method also provides flexibility to monitor the
performance and configuration of an entire chain or part thereof as
desired. This method is extensible to monitoring other KPIs. Please
refer to [RFC7665] for an architectural context for this document.
The method described in this document is not an OAM protocol such as
[Y.1731] or [Y.1564]. As such it does not define new OAM packet types
or operation. Rather it monitors the service function chain
performance and configuration for subscriber payloads and indicates
subscriber QoE rather than out-of-band infrastructure metrics. This
document differs from to [I-D.ippm.ioam] in the sense that it is
specifically tied to NSH operation and not generic in nature.
2. Terminology
2.1. Requirement 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 BCP 14
[RFC2119][RFC8174] when, and only when, they appear in all capitals,
as shown here.
2.2. Definition of Terms
This section presents the main terms used in this document. This
document makes use of the terms defined in [RFC7665] and [RFC8300].
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2.2.1. Terms Defined in this Document
First Stamping Node (FSN): The first node along a service function
chain that stamps packets using KPI stamping. The FSN matches each
packet with a Stamping Controller flow based on a stamping
classification criterion such as transport 5-tuple coordinates, but
not limited to.
Last Stamping Node (LSN): The last node along a service function
chain that stamps packets using KPI stamping. From forwarding point
of view the LSN removes the NSH header and forwards the raw IP packet
to the next hop. From a control plane point of view the LSN reads all
the metadata and exports it to a system performance statistics agent
or repository. The LSN should use the NSH Service Index (SI) to
indicate if a SF was at the end of the chain. The LSN may change the
Service Path Identifier (SPI) to preconfigured value in order that
the network underlay forwards the metadata back directly to the KPI
database (KPIDB) based on this value.
Key Performance Indicator Database (KPIDB): denotes the external
storage of metadata for reporting, trend analysis, etc.
KPI-stamping: The insertion of latency-related and/or QoS-related
information into a packet using NSH metadata.
Flow ID: The Flow ID is a unique 16 bit identifier written into the
header by the classifier. This allows 65536 flows to be concurrently
stamped on any given NSH service chain (SPI).
QoS-stamping: The insertion of QoS-related information into a packet
using NSH metadata.
Stamping Controller (SC): The SC is the central logic that decides
what packets to stamp and how. The SC instructs the classifier on how
to build the KPI stamp specific parts of the NSH.
Stamp Control Plane (SCP): the control plane between the FSN and the
SC.
2.3. Abbreviations
DEI Drop Eligible Indicator
DSCP Differentiated Services Code Point
FSN First Stamping Node
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KPI Key Performance Indicator
KPIDB Key Performance Indicator Database
LSN Last Stamping Node
MD Metadata
NFV Network Function Virtualization
NFVI-PoP NFV Infrastructure Point of Presence
NIC Network Interface Card
NSH Network Service Header
OAM Operations, Administration, and Maintenance
PCP Priority Code Point
PNF Physical Network Function
PNFN Physical Network Function Node
QoE Quality of Experience
QoS Quality of Service
QS QoS Stamp
RSP Rendered Service Path
SC Stamping Controller
SCL Service Classifier
SCP Stamp Control Plane
SI Service Index
SF Service Function
SFC Service Function Chain
SFP Service Function Path
SSI Stamp Service Index
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TC Traffic Class
TS Timestamp
VLAN Virtual Local Area Network
VNF Virtual Network Function
vSwitch Virtual Switch
3. NSH KPI Stamping: An Overview
A typical KPI stamping architecture is presented in Figure 1.
Stamping
Controller
| KPIDB
| SCP Interface |
,---. ,---. ,---. ,---.
/ \ / \ / \ / \
( SCL )-------->( SF1 )--------->( SF2 )--------->( SFn )
\ FSN / \ / \ / \ LSN /
`---' `---' `---' `---'
Figure 1: Logical roles in NSH KPI Stamping
The Stamping Controller (SC) will be part of the SFC control plane
architecture, but it is described separately in this document for
clarity.
The SC is responsible for initiating start/stop stamp requests to the
SCL or First Stamp Node (FSN), and also for distributing NSH stamping
policy into the service chain via the Stamping Control Plane (SCP)
interface.
The FSN will typically be part of the SCL, but again is called out as
separate logical entity for clarity.
The FSN is responsible for marking NSH MD fields which tells nodes in
the service chain how to behave in terms of stamping at SF ingress,
egress or both, or ignoring the stamp NSH metadata completely.
The FSN also writes the Reference Time value, a (possibly inaccurate)
estimate of the current time-of-day, into the header, allowing the
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{SPI:Flow ID} performance to be compared to previous samples for
offline analysis.
The FSN should return an error to the SC if not synchronized to the
current time-of-day and forward the packet along the service-chain
unchanged. The code and format of the error is specific to the
protocol used between the FSN and SC; these considerations are out of
scope.
SF1 and SF2 stamp the packets as dictated by the FSN and process the
payload as per normal.
Note 1: The exact location of the stamp creation may not be in
the SF itself, as discussed in Section 3.3.
Note 2: Special cases exist where some of the SFs are
NSH-unaware. This is covered in Section 5.
The Last Stamp Node (LSN) should strip the entire NSH header and
forward the raw packet to the IP next hop as per [RFC8300]. The LSN
also exports NSH stamp information to the KPI Database (KPIDB) for
offline analysis; the LSN may either export the stamping information
of all packets, or a subset based on packet sampling.
In fully virtualized environments the LSN is likely to be co-located
with the SF that decrements the NSH Service Index (SI) to zero.
Corner cases exist whereby this is not the case and is covered in
Section 5.
3.1. Prerequisites
Timestamping presents a set of prerequisites not required to QoS-
Stamp. In order to guarantee metadata accuracy, all servers hosting
VNFs should be synchronized from a centralized stable clock. As it is
assumed that PNFs do not timestamp (as this would involve a software
change and probable throughput performance impact) there is no need
for them to synchronize. There are two possible levels of
synchronization:
Level A: Low accuracy time-of-day synchronization, based on
NTP [RFC5905].
Level B: High accuracy synchronization (typically on the order of
microseconds), based on [IEEE1588].
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Each SF SHOULD have a level A synchronization, and MAY have a level B
synchronization.
Level A requires each platform (including the Stamp Controller) to
synchronize its system real-time-clock to an NTP server. This is used
to mark the metadata in the chain, using the <Reference Time> field
in the NSH KPI-stamp header (Section 4.2). This timestamp is inserted
to the NSH by the first SF in the chain. NTP accuracy can vary by
several milliseconds between locations. This is not an issue as the
Reference Time is merely being used as a time-of-day reference
inserted into the KPIDB for performance monitoring and metadata
retrieval.
Level B synchronization requires each platform to be synchronized to
a Primary Reference Time Clock (PRTC) using the Precision Time
Protocol [IEEE1588]. A platform MAY also use Synchronous Ethernet
([G.8261], [G.8262], [G.8264]), allowing more accurate frequency
synchronization.
If an SF is not synchronized at the moment of timestamping, it should
indicate its synchronization status in the NSH. This is described in
more detail in Section 4.
By synchronizing the network in this way, the timestamping operation
is independent of the current Rendered Service Path (RSP). Indeed the
timestamp metadata can indicate where a chain has been moved due to a
resource starvation event as indicated in Figure 2, between VNF 3 and
VNF 4 at time B.
Delay
| v
| v
| x
| x x = reference time A
| xv v = reference time B
| xv
| xv
|______|______|______|______|______|_____
VNF1 VNF2 VNF3 VNF4 VNF5
Figure 2: Flow performance in a service chain
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For QoS-stamping it is desired that the SCL or FSN be synchronized in
order to provide reference time for offline analysis, but this is not
a hard requirement (they may be in holdover or free-run state, for
example). Other SFs in the service chain do not need to be
synchronized for QoS-stamping operation as described below.
QoS-stamping can be used to check consistency of configuration across
the entire chain or part thereof. By adding all potential layer 2 and
layer 3 QoS fields into a QoS sum at SF ingress or egress, this
allows quick identification of QoS mismatches across multiple L2/L3
fields which otherwise is a manual, expert-led consuming process.
|
|
| xy
| xy x = ingress QoS sum
| xv v = egress QoS sum
| xv y = egress QoS sum miss
| xv
|______|______|______|______|______|_____
SF1 SF2 SF3 SF4 SF5
Figure 3: Flow QoS Consistency in a service chain
Referring to Figure 3, x, v, and y are notional sum values of the QoS
marking configuration of the flow within a given chain. As the
encapsulation of the flow can change from hop to hop in terms of VLAN
header(s), MPLS labels, DSCP(s) these values are used to compare
consistency of configuration from for example payload DSCP through
overlay and underlay QoS settings in VLAN IEEE 802.1Q bits, MPLS bits
and infrastructure DSCPs.
Figure 3 indicates that at SF4 in the chain, the egress QoS marking
is inconsistent. That is, the ingress QoS settings do not match the
egress. The method described here will indicate which QoS field(s) is
inconsistent, and whether this is ingress (whereby the underlay has
incorrectly marked and queued the packet) or egress (where the SF has
incorrectly marked and queued the packet.
Note that the SC must be aware of when a SF remarks QoS fields
deliberately and thus does not flag an issue for desired behavior.
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3.2. Operation
KPI-stamping detection mode uses MD type 2 defined in [RFC8300]. This
involves the SFC classifier stamping the flow at chain ingress, and
no subsequent stamps being applied, rather each SF upstream can
compare its local condition with the ingress value and take
appropriate action. Therefore detection mode is very efficient in
terms of header size that does not grow after the classification.
This is further explained in Section 4.1.
3.2.1. Flow Selection
The SC should maintain a list of flows within each service chain to
be monitored. This flow table should be in the format 'SPI:FlowID'.
The SC should map these pairs to unique values presented as Flow IDs
per service chain within the NSH TLV specified in this document. The
SC should instruct the FSN to initiate timestamping on flow table
match. The SC may also tell the classifier the duration of the
timestamping operation, either by a number of packets in the flow or
by a time duration.
In this way the system can monitor the performance of the all en-
route traffic, or an individual subscriber in a chain, or just a
specific application or a QoS class that is used in the network.
The SC should write the list of monitored flows into the KPIDB for
correlation of performance and configuration data. Thus, when the
KPIDB receives data from the LSN it understands to which flow the
data pertains.
The association of source IP to subscriber identity is outside the
scope of this document and will vary by network application. For
example, the method of association of a source IP to IMSI will be
different to how a CPE with NAT function may be chained in an
enterprise NFV application.
3.2.2. SCP Interface
A Stamp Control Plane (SCP) interface is required between the SC and
the FSN or classifier. This interface is used to:
o Query the SFC classifier for a list of active chains and flows.
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o Communicate which chains and flows to stamp. This can be a
specific {SPI:Flow ID} combination or include wildcards for
monitoring subscribers across multiple chains or multiple flows
within one chain.
o Instruct how the stamp should be applied (ingress, egress, both
or specific).
o Indicate when to stop stamping, either after a certain number
of packets or duration.
Typically SCP timestamps flows for a certain duration for trend
analysis, but only stamps one packet of each QoS class in a chain
periodically (perhaps once per day or after a network change).
Therefore, timestamping is generally applied to a much larger set of
packets than QoS-stamping.
Exact specification of SCP is for further study.
3.3. Performance Considerations
This document does not mandate a specific stamping implementation
method, and thus NSH KPI stamping can either be performed by hardware
mechanisms, or by software.
If software-based stamping is used, applying and operating on the
stamps themselves incur an additional small delay in the service
chain. However, it can be assumed that these additional delays are
all relative for the flow in question. This is only pertinent for
timestamping mode, and not for QoS-stamping mode. Thus, whilst the
absolute timestamps may not be fully accurate for normal non-
timestamped traffic they can be assumed to be relative.
It is assumed that the method described in this document would only
operate on a small percentage of user flows.
The service provider may choose a flexible policy in the SC to
timestamp a selection of user-plane every minute for example to
highlight any performance issues. Alternatively, the LSN may
selectively export a subset of the KPI-stamps it receives, based on a
predefined sampling method. Of course the SC can stress test an
individual flow or chain should a deeper analysis be required. We can
expect that this type of deep analysis has an impact on the
performance of the chain itself whilst under investigation. The
impact will be dependent on vendor implementation and outside the
scope of this document.
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For QoS-stamping the method described here is even less intrusive, as
typically multiple packets in a flow are QoS stamped periodically
(perhaps once per day) check one packet in a chain per QoS class.
4. NSH KPI-stamping Encapsulation
KPI stamping uses NSH MD type 0x2 for detection of anomalies and
extended mode for root cause analysis of KPI violations. These are
further explained in this section.
The generic NSH MD type 2 TLV for KPI Stamping is shown below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|O|U| TTL | Length |U|U|U|U|Type=2 | Next Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Path Identifier | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class | Type |U| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable-length KPI Metadata header and TLV(s) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Generic NSH KPI Encapsulation
Relevant fields in header that the FSN must implement:
o The O bit must not be set.
o The MD type must be set to 0x2
o The Metadata Class must be set to a value from the experimental
range 0xfff6 to 0xfffe according to an agreement by all parties to
the experiment.
o Unassigned bits: all fields, marked U, are unassigned and
available for future use [RFC8300]
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o The Type field may have one of the following values; the
content of "KPI metadata" depends on the type value:
o Type = 0x01 Det: Detection
o Type = 0x02 TS: Timestamp Extended
o Type = 0x03 QoS: QoS-stamp Extended
The Type field determines the type of KPI-stamping format. The
supported formats are presented in the following subsections.
4.1. KPI-stamping Extended Encapsulation
The generic NSH MD type 2 KPI-stamping header extended mode is shown
in Figure 5. This is the format for performance monitoring of service
chain issues with respect to QoS configuration and latency.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|O|U| TTL | Length |U|U|U|U|Type=2 | Next Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Path Identifier | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class | Type |U| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable Length KPI Configuration Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable Length KPI Value (LSN) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable Length KPI Value (FSN) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Generic KPI Encapsulation (Extended Mode)
As mentioned above, two types are defined under the experimental MD
class to indicate extended KPI MD: a timestamp type and a QoS-stamp
type.
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The KPI Encapsulation Configuration Header format is shown below.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|K|K|T|K|K|K|K|K| Stamping SI | Flow ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reference Time |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: KPI Encapsulation Configuration Header
The bits marked as 'K' are reserved for specific KPI type use and
described in the corresponding subsections below.
The T bit should be set if Reference Time follows KPI Encapsulation
Configuration Header.
Stamping Service Index (Stamping SI) contains the Service Index used
for KPI stamping and described in the corresponding subsections
below.
The Flow ID is a unique 16 bit identifier written into the header by
the classifier. This allows 65536 flows to be concurrently stamped on
any given NSH service chain (SPI). Flow IDs are not written by
subsequent SFs in the chain. The FSN may export monitored flow IDs to
the KPIDB for correlation.
Reference Time is the wall clock of the FSN, and may be used for
historical comparison of SC performance. If the FSN is not Level A
synchronized (see Section 3.1) it should inform the SC over the SCP
interface. The Reference Time is represented in 64-bit NTP format
[RFC5905] presented in Figure 7:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fraction |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: NTP [RFC5905] 64-bit Timestamp Format
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4.1.1. NSH Timestamping Encapsulation (Extended Mode)
The NSH timestamping extended encapsulation 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|O|C|U|U|U|U|U|U| Length |U|U|U|U|Type=2 | NextProto |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Path ID | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class | Type=TS(2) |U| Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|I|E|T|U|U|U|SSI| Stamping SI | Flow ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| Reference Time (T bit is set) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|I|E|U|U|U| SYN | Stamping SI | Unassigned |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| Ingress Timestamp (I bit is set)(LSN) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress Timestamp (E bit is set)(LSN) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|I|E|U|U|U| SYN | Stamping SI | Unassigned |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| Ingress Timestamp (I bit is set) (FSN) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress Timestamp (E bit is set) (FSN) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: NSH Timestamp Encapsulation (Extended Mode)
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The FSN KPI-stamp metadata starts with Stamping Configuration Header.
This header contains the I, E, T bits and Stamp Service Index (SSI).
The I bit should be set if Ingress stamp is requested.
The E bit should be set if Egress stamp is requested.
SSI field must be set to one of the following values:
o 0x0 KPI-stamp mode, no Service index specified in the Stamp
Service Index field.
o 0x1 KPI-stamp Hybrid mode is selected, Stamp Service Index
contains LSN Service index. This is used when PNFs or NSH-unaware
SFs are used at the tail of the chain. If SSI=0x1, then the value
in the type field informs the chain which SF should act as the
LSN.
o 0x2 KPI-stamp Specific mode is selected, Stamp Service Index
contains the targeted Service Index. In this case the Stamp
Service Index field indicates which SF is to be stamped. Both
ingress and egress stamps are performed when the SI=SSI on the
chain. For timestamping mode, the FSN will also apply the
Reference Time and Ingress Timestamp. This will indicate the delay
along the entire service chain to the targeted SF. This method may
also be used as a light implementation to monitor end-to-end
service chain performance whereby the targeted SF is the LSN. This
is not applicable to QoSStamping mode.
Each stamping Node adds stamping metadata which consist of Stamping
Reporting Header and timestamps.
The E bit should be set if Egress stamp is reported.
The I bit should be set if Ingress stamp is reported.
With respect to timestamping mode, the SYN bits are an indication of
the synchronization status of the node performing the timestamp and
must be set to one of the following values:
o In Synch: 0x00
o In holdover: 0x01
o In free run: 0x02
o Out of Synch: 0x03
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If the platform hosting the SF is out of synch or in free run no
timestamp is applied by the node and the packet is processed
normally.
If FSN is out of synch or in free run timestamp request rejected and
not propagated though the chain. The FSN should inform the SC in such
an event over the SCP interface. Similarly if KPIDB receives
timestamps that are out of order (i.e. a time stamp of a 'N+1' SF is
in the past of a 'N' SF) it should notify SC of this condition over
the SCP interface.
The outer service index value is copied into the stamp metadata as
Stamping SI to help cater for hybrid chains that are a mix of VNFs
and PNFs or through NSH-unaware SFs. Thus, if a flow transits through
a PNF or an NSH-unaware node the delta in the inner service index
between timestamps will indicate this.
The Ingress Timestamp and Egress Timestamp are represented in 64-bit
NTP format. The corresponding bits (I and E) reported in the Stamping
Reporting Header of the node's metadata.
4.1.2. NSH QoS-stamping Encapsulation (Extended Mode)
Packets have a variable QoS stack. That is for example the same
payload IP can have a very different stack in the access part of the
network to the core. This is most apparent in mobile networks where
for example in an access circuit we would have 2 layers of
infrastructure IP header (DSCP) - one transport-based and the other
IPsec-based, in addition to multiple MPLS and VLAN tags. The same
packet as it leaves the PDN Gateway Gi egress interface may be very
much simplified in terms of overhead and related QoS fields.
Because of this variability we need to build extra meaning into the
QoS headers - they are not for example all PTP timestamps of a fixed
length as in the case of timestamping, rather they are variable
lengths and types. Also they can be changed on the underlay at any
time without knowledge by the SFC system. Therefore each SF must be
able to ascertain and record its ingress and egress QoS configuration
on the fly.
The suggested QoS type, lengths are as below. The type is 4 bits
long.
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QoS Type(QT)Value Length Comment
IVLAN 0x01 4 Bits Ingress VLAN (PCP + DEI)
EVLAN 0x02 4 Bits Egress VLAN
IQINQ 0x03 8 Bits Ingress QinQ (2x PCP+DEI)
EQINQ 0x04 8 Bits Egress QinQ
IMPLS 0x05 3 Bits Ingress Label
EMPLS 0x06 3 Bits Egress Label
IMPLS 0x07 6 Bits 2 Ingress Labels (2x EXP)
EMPLS 0x08 6 Bits 2 Egress Labels
IDSCP 0x09 8 Bits Ingress DSCP
EDSCP 0x0A 8 Bits Egress DSCP
For stacked headers such as MPLS and 802.1ad, we extract the QoS
relevant data from the header and insert into one QoS value in order to
be more efficient on packet size. Thus for MPLS, we represent both EXP
fields in one QoS value, and both 802.1p priority and drop precedence in
one QoS value as indicated above.
For stack types not listed here, for example, 3 or more MPLS tags, SF
would insert IMPLS/EMPLS several times with each layer in the stack
indicating EXP Qos for that layer.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|O|C|U|U|U|U|U|U| Length |U|U|U|U|Type=2 | NextProto=0x0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Path ID | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class | Type=QoS(3) |U| Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|U|T|U|U|U|SSI| Stamping SI | Flow ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| Reference Time (T bit is set) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|U|U|U|U|U|U|U| Stamping SI | Unassigned |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| QT | QoS Value |U|U|U|E| QT | QoS Value |U|U|U|E|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|U|U|U|U|U|U|U| Stamping SI | Unassigned |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| QT | QoS Value |U|U|U|E| QT | QoS Value |U|U|U|E|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: NSH QoS Configuration Encapsulation (Extended Mode)
The encapsulation in Figure 10 is very similar to that detailed in
Section 4.1 with the following exceptions:
- I and E bits are not required as we wish to examine the full QoS
stack at ingress and egress at every SF.
- Syn status bits are not required.
- The QT (QoS Type) and QoS value are as outlined in the table
above.
- The E bit at the tail of each QoS context field indicates if this
is the last egress QoS-stamp for a given SF. This should coincide
with SI=0 at the LSN, whereby the packet is truncated and the NSH
MD sent to the KPIDB and the subscriber raw IP packet forwarded to
the underlay next hop.
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Note: It is possible to compress the frame structure to better
utilize the header, but this would come at the expense of crossing
byte boundaries. For ease of implementation, and that QoS-stamping is
applied on an extremely small subset of user plane traffic, we
believe the above structure is a pragmatic compromise between header
efficiency and ease of implementation.
4.2. KPI-stamping Encapsulation (Detection Mode)
The format of the NSH MD type 2 KPI-stamping TLV (detection mode) is
shown in Figure 11.
This TLV is used for KPI anomaly detection. Upon detecting a problem
or an anomaly it will be possible to enable the use of KPI-stamping
extended encapsulations, which will provide more detailed analysis.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|O|U| TTL | Length |U|U|U|U|Type=2 | Next Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Path Identifier | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class | Type=Det(1) |U| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| KPI Type | Stamping SI | Flow ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold KPI Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ingress KPI-stamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Generic NSH KPI Encapsulation (Detection Mode)
The following fields are defined in the KPI TSD metadata:
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o KPI Type: determines the type of KPI-stamp that is included in
this metadata field.
If a receiver along the path does not understand the KPI Type it
will pass the packet transparently and not drop.
The supported values of the KPI Type are:
0x0 Timestamp
0x1 QoS-stamp
o Threshold KPI Value: In the first header the SFC classifier may
program a KPI threshold value. This is a value that when exceeded,
requires the SF to insert the current SI value into the SI field.
The KPI type is the type of KPI stamp inserted into the header as
per section 9.
o Stamping SI: Service Identifier of the SF when the Threshold
above is exceeded.
o Flow ID: The flow ID is inserted into the header by the SFC
classifier in order to correlate flow data in the KPIDB for
offline analysis.
o Ingress KPI-stamp: The last 8 octets are reserved for the KPI-
stamp. This is the KPI value at the chain ingress at the SFC
classifier. Depending on the KPI Type, the KPI-stamp either
includes a timestamp or a QoS-stamp.
If the KPI Type is Timestamp, then the Ingress KPI-stamp field
contains a timestamp in 64-bit NTP timestamp format. If the KPI
Type is QoS-stamp, then the format of the 64-bit Ingress KPI-stamp
is as follows.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QT | QoS Value | Unassigned |
+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: QoS-stamp Format (Detection Mode)
As an example operation, say we are using KPI type 0x01 (timestamp)
when a service function (SFn) receives the packet it can compare
current local timestamp (it first checks that it is synchronized to
network PRC) with chain ingress timestamp to calculate the latency in
the chain. If this value exceeds the timestamp threshold, it then
inserts its SI and returns the NSH to the KPIDB. This effectively
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tells the system that at SFn the packet violated the KPI threshold.
Please refer to figure 9 for timestamp format.
When this occurs the SFC control plane system would then invoke the
KPI extended mode, which uses a more sophisticated (and intrusive)
method to isolate KPI violation root cause as described below.
Note: Whilst detection mode is a valuable tool for latency actions,
the authors feel that it is not justified to build the logic into the
KPI system for QoS configuration. As QoS-stamping is done
infrequently and on a tiny percentage of user plane, it is more
practical to use extended mode only for service chain QoS
verification.
5. Hybrid Models
A hybrid chain may be defined as a chain whereby there is a mix of
NSH-aware and NSH-unaware SFs.
Example 1. PNF in the middle
Stamp
Controller
| KPIDB
| SCP Interface |
,---. ,---. ,---. ,---.
/ \ / \ / \ / \
( SCL )-------->( SF1 )--------->( SF2 )--------->( SFn )
\ FSN / \ / \ PNF1/ \ LSN /
`---' `---' `---' `---'
Figure 12: Hybrid chain with PNF in middle
In this example the FSN begins operation and sets the SI to 3, SF1
decrements this to 2 and passes the packet to an SFC proxy (not
shown).
The SFC proxy strips the NSH and passes to the PNF. On receipt back
from the PNF, the proxy decrements the SI and passes the packet onto
the LSN with a SI=1.
After the LSN processes the traffic it knows it is the last node on
the chain from the SI value and exports the entire NSH and all
metadata to the KPIDB. The payload is forwarded to the next hop on
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the underlay minus the NSH. The stamping information packet may be
given a new SPI to act as a homing tag to transport the stamp data
back to the KPIDB.
Example 2. PNF at the end
Stamp
Controller
| KPIDB
| SCP Interface |
,---. ,---. ,---. ,---.
/ \ / \ / \ / \
( SCL )-------->( SF1 )--------->( SF2 )--------->( PNFN )
\ FSN / \ / \ LSN / \ /
`---' `---' `---' `---'
Figure 13: Hybrid Chain with PNF at end
In this example the FSN begins operation and sets the SI to 3, the
SSI field set to 0x1, and the type to 1. Thus, when SF2 receives the
packet with SI=1, it understands that it is expected to take on the
role of the LSN as it is the last NSH-aware node in the chain.
5.1. Targeted VNF Stamp
For the majority of flows within the service chain, stamps (ingress,
egress or both) will be carried out at each hop until the SI
decrements to zero and the NSH and Stamp MD is exported to the KPIDB.
There may exist however the need to just test a particular VNF
(perhaps after a scale out operation, software upgrade or underlay
change for example). In this case the FSN should mark the NSH as
follows:
SSI field is set to 0x2. Type is set to the expected SI at the SF in
question. When outer SI is equal to the SSI, stamps are applied at SF
ingress and egress, and the NSH and MD are exported to the KPIDB.
6. Fragmentation Considerations
The method described in this document does not support fragmentation.
The SC should return an error should a stamping request from an
external system exceed MTU limits and require fragmentation.
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Depending on the length of the payload and the type of KPI-stamp and
chain length, this will vary for each packet.
In most service provider architectures we would expect a SI << 10,
and that may include some PNFs in the chain which do not add
overhead. Thus for typical IMIX packet sizes we expect to able to
perform timestamping on the vast majority of flows without
fragmenting. Thus the classifier can have a simple rule to only allow
KPI-stamping on packet sizes less than 1200 bytes for example.
7. Security Considerations
The security considerations of NSH in general are discussed in
[RFC8300].
The use of in-band timestamping, as defined in this document, can be
used as a means for network reconnaissance. By passively
eavesdropping to timestamped traffic, an attacker can gather
information about network delays and performance bottlenecks.
The NSH timestamp is intended to be used by various applications to
monitor the network performance and to detect anomalies. Thus, a man-
in-the-middle attacker can maliciously modify timestamps in order to
attack applications that use the timestamp values. For example, an
attacker could manipulate the SFC classifier operation, such that it
forwards traffic through 'better' behaving chains. Furthermore, if
timestamping is performed on a fraction of the traffic, an attacker
can selectively induce synthetic delay only to timestamped packets,
causing systematic error in the measurements.
Similarly, if an attacker can modify QoS stamps, erroneous values may
be imported into the KPIDB, resulting is further misconfiguration and
subscriber QoE impairment.
An attacker that gains access to the SCP can enable time and QoS-
stamping for all subscriber flows, thereby causing performance
bottlenecks, fragmentation, or outages.
As discussed in previous sections, NSH timestamping relies on an
underlying time synchronization protocol. Thus, by attacking the time
protocol an attack can potentially compromise the integrity of the
NSH timestamp. A detailed discussion about the threats against time
protocols and how to mitigate them is presented in [RFC7384].
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8. IANA Considerations
This document makes no requests for IANA action,
9. Contributors
This document originated as draft-browne-sfc-nsh-timestamp-00 and had
the following co-authors and contributors. We would like to thank and
recognize them and their contributions.
Yoram Moses
Technion
moses@ee.technion.ac.il
Brendan Ryan
Intel Corporation
brendan.ryan@intel.com
10. Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot.
The authors gratefully acknowledge Mohamed Boucadair, Martin
Vigoureux and Adrian Farrel for their thorough reviews and helpful
comments.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC7665] Halpern, J., Ed., and C. Pignataro, Ed., "Service
Function Chaining (SFC) Architecture", RFC 7665, DOI
10.17487/RFC7665, October 2015, <https://www.rfc-
editor.org/info/rfc7665>.
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[RFC8174] B. Leiba, "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", RFC8174, May 2017.
[RFC8300] Quinn, P., Elzur, U., Pignataro, C., "Network Service
Header (NSH)", RFC 8300, 2018.
11.2. Informative References
[IEEE1588] IEEE TC 9 Instrumentation and Measurement Society,
"1588 IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and
Control Systems Version 2", IEEE Standard, 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26, RFC
5226, May 2008.
[RFC5905] Mills, D., Martin, J., Burbank, J., Kasch, W.,
"Network Time Protocol Version 4: Protocol and
Algorithms Specification", RFC 5905, June 2010.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols
in Packet Switched Networks", RFC 7384, October 2014.
[TS] Mizrahi, T., Fabini, J., and A. Morton, "Guidelines
for Defining Packet Timestamps", draft-ietf-ntp-
packet-timestamps (work in progress), 2018.
[Y.1731] ITU-T Recommendation G.8013/Y.1731, "OAM Functions and
Mechanisms for Ethernet-based Networks", August 2015.
[Y.1564] ITU-T Recommendation Y.1564, "Ethernet service
activation test methodology", March 2011.
[G.8261] ITU-T Recommendation G.8261/Y.1361, "Timing and
synchronization aspects in packet networks", August
2013.
[G.8262] ITU-T Recommendation G.8262/Y.1362, "Timing
characteristics of a synchronous Ethernet equipment
slave clock", January 2015.
[G.8264] ITU-T Recommendation G.8264/Y.1364, "Distribution of
timing information through packet networks", May 2014.
[I-D.ippm.ioam]
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Brockners, Bhandari et al. "Data Fields for In-situ OAM"
draft-ietf-ippm-ioam-data-03 (work in progress), June
2018
Authors' Addresses
Rory Browne
Intel
Dromore House
Shannon
Co.Clare
Ireland
Email: rory.browne@intel.com
Andrey Chilikin
Intel
Dromore House
Shannon
Co.Clare
Ireland
Email: andrey.chilikin@intel.com
Tal Mizrahi
Huawei Network.IO Innovation Lab
Israel
Email: tal.mizrahi.phd@gmail.com
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