One document matched: draft-bryant-mpls-synonymous-flow-labels-01.xml
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<rfc category="std" docName="draft-bryant-mpls-synonymous-flow-labels-01"
ipr="trust200902" updates="">
<front>
<title abbrev="Synonymous Labels ">RFC6374 Synonymous Flow Labels</title>
<author fullname="Stewart Bryant" initials="S" surname="Bryant">
<organization>Cisco Systems</organization>
<address>
<email>stbryant@cisco.com</email>
</address>
</author>
<author fullname="George Swallow" initials="G" surname="Swallow">
<organization>Cisco Systems</organization>
<address>
<email>swallow@cisco.com</email>
</address>
</author>
<author fullname="Siva Sivabalan" initials="S " surname="Sivabalan">
<organization>Cisco Systems</organization>
<address>
<email>msiva@cisco.com</email>
</address>
</author>
<author fullname="Greg Mirsky" initials="G" surname="Mirsky">
<organization>Ericsson</organization>
<address>
<email>gregory.mirsky@ericsson.com</email>
</address>
</author>
<author fullname="Mach(Guoyi) Chen" initials="M" surname="Chen">
<organization>Huawei</organization>
<address>
<email>mach.chen@huawei.com</email>
</address>
</author>
<author fullname="Zhenbin(Robin) Li" initials="Z" surname="Li">
<organization>Huawei</organization>
<address>
<email>lizhenbin@huawei.com</email>
</address>
</author>
<date year="2015" />
<area>Routing</area>
<workgroup>MPLS</workgroup>
<keyword>OAM</keyword>
<keyword></keyword>
<keyword>Internet-Draft</keyword>
<abstract>
<t>[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.]</t>
<t>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.</t>
</abstract>
</front>
<middle>
<section anchor="INTRO" title="Introduction">
<t><xref target="I-D.bryant-mpls-flow-ident"></xref> describes the
requirement for introducing flow identities when using RFC6374 <xref
target="RFC6374"></xref> 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:</t>
<t><list style="numbers">
<t>Where a flow is subjected to Equal Cost Multi-Path (ECMP)
treatment packets can arrive out of order with respect to the LM
packet.</t>
<t>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.</t>
<t>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.</t>
<t>Link aggregation techniques may also lead to synchronization
issues.</t>
<t>Some forwarder implementations have a long pipeline between
processing a packet and incrementing the associated counter again
leading to synchronization difficulties.</t>
</list></t>
<t>An approach to mitigating these synchronization issue is described in
<xref target="I-D.tempia-ippm-p3m"></xref> and <xref
target="I-D.chen-ippm-coloring-based-ipfpm-framework"></xref> 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.</t>
<t>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.</t>
<t>This document describes a method of accomplishing this by using a
technique called Synonymous Flow Labels (SFL) <xref
target="SFLSECT">(see</xref>) in which labels which mimic the behaviour
of other labels provide the packet batch identifiers and enable the per
batch packet accounting.</t>
</section>
<section title="Requirements Language">
<t>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 <xref
target="RFC2119"></xref>.</t>
</section>
<section anchor="SFLSECT" title="Synonymous Flow Labels">
<t>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. </t>
<t>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).</t>
<t>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.</t>
<t>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.</t>
<t>Note that to achieve the goals set out in <xref
target="INTRO"></xref> SLs need to be allocated from the platform label
table.</t>
</section>
<section anchor="UST" title="User Service Traffic in the Data Plane">
<t>As noted in <xref target="SFLSECT"></xref> it is necessary to
consider two cases:<list style="numbers">
<t>Applications label present</t>
<t>Single label stack</t>
</list></t>
<section anchor="ALP" title="Applications Label Present">
<t><xref target="SFL-Stack"></xref> 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.</t>
<figure anchor="SFL-Stack"
title="Use of Synonymous Labels In A Two Label MPLS Label Stack">
<artwork><![CDATA[
+-----------------+ +-----------------+
| | | |
| LSP | | LSP | <May be PHPed
| Label | | Label |
+-----------------+ +-----------------+
| | | |
| Application | | Synonymous Flow |
| Label | | Label |
+-----------------+ +-----------------+ <= Bottom of stack
| | | |
| Payload | | Payload |
| | | |
+-----------------+ +-----------------+
"Normal" Label Stack Label Stack with SFL
]]></artwork>
</figure>
<t>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.</t>
<t>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 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.</t>
<t></t>
<section title="Setting TTL and the Traffic Class Bits">
<t>To be provided in a future version of this draft.</t>
</section>
</section>
<section anchor="SLS" title="Single Label Stack">
<t><xref target="SFL-Stack2"></xref> 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.</t>
<figure anchor="SFL-Stack2"
title="Use of Synonymous Labels In A Single Label MPLS Label Stack">
<artwork><![CDATA[ +-----------------+
| |
| 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
]]></artwork>
</figure>
<t>At the receiving LSR it is necessary to consider two cases:</t>
<t><list style="numbers">
<t>Where the LSP label is still present</t>
<t>Where the LSP label is penultimate hop popped</t>
</list>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
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.</t>
<t>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. </t>
<section title="Setting TTL and the Traffic Class Bits">
<t>To be provided in a future version of this draft.</t>
</section>
</section>
<section title="Aggregation of SFL Actions">
<t>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 <xref target="SLS"></xref>,
and the same signalling, management and configuration tools would be
applicable.</t>
<t></t>
<figure anchor="SFL-Agg" title="Aggregate SFL Actions">
<artwork><![CDATA[ +-----------------+
| |
| 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
]]></artwork>
</figure>
<t></t>
<t>The Aggregate SFL is shown in the label stack depicted in <xref
target="SFL-Agg"></xref> 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 <xref
target="ALP"></xref>, 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. </t>
<t>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.</t>
</section>
</section>
<section title="Equal Cost Multipath Considerations">
<t>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:</t>
<t><list style="numbers">
<t>The operator can elect to always run with the SFL in place in the
MPLS label stack.</t>
<t>The operator can elect to use <xref target="RFC6790"></xref>
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.</t>
</list></t>
</section>
<section title="RFC6374 Packet Loss Measurement with SFL">
<t>The packet format of an RFC6374 Query message using SFLs is shown in
<xref target="RFC6374MSG"></xref>.</t>
<figure anchor="RFC6374MSG" title="RFC6734 Query Packet with SFL">
<artwork><![CDATA[ +-------------------------------+
| |
| LSP |
| Label |
+-------------------------------+
| |
| Synonymous Flow |
| Label |
+-------------------------------+
| |
| |
| RFC6374 Measurement Message |
| |
| +-------------------------+ |
| | | |
| | RFC6374 Fixed | |
| | Header | |
| | | |
| +-------------------------+ |
| | | |
| | Optional SFL TLV | |
| | | |
| +-------------------------+ |
| | | |
| | Optional Return | |
| | Information | |
| | | |
| +-------------------------+ |
| |
+-------------------------------+ ]]></artwork>
</figure>
<t></t>
<t>The MPLS label stack is exactly the same as that used for the user
data service packets being instrumented (see <xref
target="UST"></xref>). The RFC6374 measurement message consists of the
three components, the RFC6374 fixed header as specified in <xref
target="RFC6374"></xref> carried over the ACH channel type specified the
type of measurement being made (currently: loss, delay or loss and
delay) as specified in RFC6374.</t>
<t>Two optional TLVs MAY also be carried if needed. The first is the SFL
TLV specified in <xref target="SFLTLVSEC"></xref>. 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.</t>
<t>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 <xref
target="I-D.ietf-mpls-rfc6374-udp-return-path"></xref>.</t>
<section anchor="SFLTLVSEC" title="RFC6374 SFL TLV">
<t>[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]</t>
<t>The required RFC6374 SFL TLV is shown in <xref
target="SFLTLV"></xref>. 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.</t>
<figure anchor="SFLTLV" title="SFL TLV">
<artwork><![CDATA[ 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 |
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Where:</t>
<t><list hangIndent="15" style="hanging">
<t hangText="Type">Type is set to Synonymous Flow Label
(SFL-TLV).</t>
<t hangText="Length">The length of the TLV as specified in <xref
target="RFC6374"></xref>.</t>
<t hangText="MBZ">MUST be sent as zero and ignored on receive.</t>
<t hangText="SFL Batch">The SFL batch that this SFL was allocated
as part of (see draft-bryant-mpls-sfl-control)</t>
<t hangText="SPL Index">The index into the list of SFLs that were
assigned against the FEC that corresponds to the SFL.</t>
<t hangText="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 <xref target="RFC3032"></xref>.</t>
<t hangText="Reserved">MUST be sent as zero and ignored on
receive.</t>
<t hangText="FEC">The Forwarding Equivalence Class that was used
to request this SFL. This is encoded as per Section 3.4.1 of</t>
</list></t>
<t>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.</t>
</section>
</section>
<section title="The Application of SFL to other PM Types">
<t>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.</t>
</section>
<section anchor="PC" title="Privacy Considerations">
<t>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.</t>
</section>
<section anchor="SEC" title="Security Considerations">
<t>The issue noted in <xref target="PC"></xref> 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.</t>
</section>
<section title="IANA Considerations">
<t>IANA is request to allocate a new TLV from the 0-127 range on the
MPLS Loss/Delay Measurement TLV Object Registry:</t>
<figure>
<artwork><![CDATA[ Type Description Reference
---- --------------------------------- ---------
TBD Synonymous Flow Label This]]></artwork>
</figure>
<t></t>
<t>A value of 4 is recommended.</t>
</section>
<section title="Acknowledgements">
<t>TBD</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include='reference.RFC.2119'?>
<?rfc include='reference.RFC.3032'?>
<?rfc include='reference.I-D.ietf-mpls-rfc6374-udp-return-path'?>
</references>
<references title="Informative References">
<?rfc include='reference.RFC.6374'?>
<?rfc include='reference.I-D.bryant-mpls-flow-ident'?>
<?rfc include='reference.I-D.tempia-ippm-p3m'?>
<?rfc include='reference.I-D.chen-ippm-coloring-based-ipfpm-framework'?>
<?rfc include='reference.RFC.6790'?>
</references>
</back>
</rfc>
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