One document matched: draft-bryant-mpls-synonymous-flow-labels-00.xml
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<rfc category="std" docName="draft-bryant-mpls-synonymous-flow-labels-00"
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>
<date year="2015" />
<area>Routing</area>
<workgroup>MPLS</workgroup>
<keyword>OAM</keyword>
<keyword></keyword>
<keyword>Internet-Draft</keyword>
<abstract>
<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. In summary RFC6374
uses the RFC6374 packet as the packet accounting demarcation point.
Unfortunately this gives rise to a number of problems that may lead to
significant packet accounting errors:</t>
<t><list style="numbers">
<t>Where a flow is subjected to Equal Cost Multi-Path (ECMP)
treatment packets may arrive out of order with respect to the
RFC6374 packet.</t>
<t>Where a flow is subjected to ECMP treatment packets may arrive at
different hardware interfaces, thus requiring reception of an
RFC6374 packet on one interface to trigger a packet accounting
action on another 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 cores,
leading to synchronization problems.</t>
<t>Some forwarder implementations have a long pipeline between
processing a packet and incrementing the associated counter.</t>
</list></t>
<t>An approach to mitigating these synchronization issue is described in
<xref target="I-D.tempia-opsawg-p3m"></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 <xref target="SFLSECT"></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>A synonymous flow label (SFL) is defined to be a label that causes
exactly the same forwarding behaviour at the egress Label Switching
Router (LSR) as another label, except that it also causes an additional
agreed action to take place on the packet. In this application the
agreed action is 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
optimization 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 form another
source. Note that the sources all operate independently and
asynchronously from each other, independently co-ordinating with the
destination.</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 he semantics are similar to an MPLS explicit
NULL. In both cases with 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 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 |
+-----------------+ +-----------------+
| | | |
| 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>
</section>
<section 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 |
+-----------------+ +-----------------+
| | | |
| Application | | Synonymous Flow | <= Explicit NULL
| Label | | Label |
+-----------------+ +-----------------+ <= Bottom of stack
| | | |
| Payload | | Payload |
| | | |
+-----------------+ +-----------------+
"Normal" Label Stack Label Stack with SFL
(Mode 1) (Mode 3)
]]></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 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 then
take the additional associated SFL action, which in this case is
packet batch counting, or 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>
</section>
<section title="RFC6374 Packet Loss Measurement">
<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-RFC63740-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="SFL TLV">
<t>The 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 | FEC >
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
> FEC cont |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></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 SPLs that were
assigned against the FEC that corresponds to the SPL.</t>
<t hangText="SFL ">The SPL 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="FEC">The Forwarding Equivalence Class that was used
to request this SPL. 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="Manageability Considerations">
<t>This will be considered in a future version of this document.</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 system described in this memo introduces no additional security
vulnerabilities.</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-opsawg-p3m'?>
</references>
</back>
</rfc>
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