One document matched: draft-bryant-mpls-sfl-control-00.xml
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<rfc category="std" docName="draft-bryant-mpls-sfl-control-00"
ipr="trust200902" updates="">
<front>
<title abbrev="SFL Control">A Control Protocol for 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>In draft-bryant-mpls-synonymous-flow-labels the concept of MPLS
synonymous flow labels (SFL) was introduced. This document describes a
control protocol that runs over an associated control header to request,
withdrawn and extend the lifetime of such labels.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>In [draft-bryant-mpls-synonymous-flow-labels] the concept of MPLS
synonymous flow labels (SFL) was introduced. This document describes a
simple control protocol that runs over an associated control header to
request, withdrawn and extend the lifetime of such labels. In
[draft-bryant-mpls-RFC63740-over-udp] it is shown how to run this over
UDP transport.</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="SFL-CTRL" title="SFL Control">
<t>This section describes the process by which the RFC6374 Querier
requests SFLs, the process by which the RFC6374 Responder sends them to
the Querier, and the process for managing the SFL lifetime. SFL Control
Messages are carried over the SFL Control ACH. The SFL ACH is carried
over a Pseudowire(PW) in place of the PW Control Word (CW), over an MPLS
LSP using the GAL, or over some other mutually agreed path. Similarly
the response may be returned over a PW, over a bidirectional LSP or over
some other mutually agreed path. See <xref target="RPATH"></xref>.</t>
<section title="SFL Control Message">
<t>The format of an SFL Control message, which follows the Associated
Channel Header (ACH), is as follows:</t>
<figure anchor="SFL-CONTROL-MSG" title="SFL Control Message Format">
<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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Flags | Control Code | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session Identifier | SFL Batch |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime (seconds) | Num SFL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SFL 0 | LFlags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SFL n | LFlags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding Equivalence Class (FEC) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t></t>
<t>Reserved fields MUST be set to 0 and ignored upon receipt. The
possible values for the remaining fields are as follows:</t>
<t><list hangIndent="15" style="hanging">
<t hangText="Version">Protocol version. Set to zero in this
specification.</t>
<t hangText="Flags">Message control flags.</t>
<t hangText="Control Code">Code identifying the query or response
type.</t>
<t hangText="Message Length">Total length of this message in
bytes.</t>
<t hangText="Session Identifier">Set arbitrarily by the querier
and used as a message handle.</t>
<t hangText="SFL Batch">Used where the SFLs for this Session
Identifier managed across multiple SFL Control Messages. A given
set of SFLs MUST be retained in the same batch.</t>
<t hangText="Lifetime">The lifetime in seconds of the SFLs in this
message. In a Query message it is the requested lifetime. In a
Response message it is the lifetime that the SFLs have been
allocated for by the Responder. The Querier MUST NOT use an SFL
after expiry of its lifetime, a Responder MUST make the SFL
available for at least its lifetime.</t>
<t hangText="Num SFL">The number of SFLs in this SFL Batch. This
MUST be constant for the lifetime of the batch.</t>
<t hangText="SFL n">The n'th SFL carried in this TLV. 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>. The position of
a label within a batch is constant for the lifetime of the batch.
Enumeration starts at zero.</t>
<t hangText="LFlags">The set of flags associated with the
immediately preceding SFL. See below.</t>
<t hangText="FEC">The Forwarding Equivalence Class that the SFLs
in this TLV correspond to. This is encoded as per Section 3.4.1 of
<xref target="RFC5036"></xref>.</t>
</list></t>
<t>Flags: The format of the Flags field is shown below.</t>
<figure title="SFL Control Message Flag">
<artwork><![CDATA[ +-+-+-+-+
|R|0|0|0|
+-+-+-+-+
]]></artwork>
</figure>
<t><list style="hanging">
<t hangText="R:">Query/Response indicator. Set to 0 for a Query
and 1 for a Response.</t>
<t hangText="0:">Set to zero by the Sender and ignored by the
Receiver.</t>
</list></t>
<t>Control Code: Set as follows according to whether the message is a
Query or a Response as identified by the R flag.</t>
<t>For a Query:</t>
<t><list style="hanging">
<t hangText="Request">This indicates that the responder is
requested to allocate the set of SFLs marked with the R LFlag in
this Message.</t>
<t hangText="Refresh">This indicates that the responder is
requested to refresh the set of SFLs marked with the V LFlag in
this Message.</t>
<t hangText="Withdraw">This indicates that the querier will no
longer use the set of SFLs marked with the V Lflag and the
responder may expire their lifetime.</t>
</list></t>
<t></t>
<t>For a Response:</t>
<t><list style="hanging">
<t hangText="Grant">This indicates that the responder allocated
the set of SFLs marked with the A LFlag in this Message.</t>
<t hangText="Refresh-Ack">This indicates that the responder has
refreshed the set of SFLs marked with the V LFlag in this Message,
and the lifetime is now as indicated by the lifetime field.</t>
<t hangText="Withdraw-Ack">This indicates that the responder has
received the Withdraw message and will withdraw the SFLs</t>
<t hangText="SFL-Unable">The Responder was unable to satisfy the
SFL Request. The details of the failure can be determined by
comparing the Request and Grant messages.</t>
</list></t>
<t>Further error codes are for future study.</t>
<t>The LFlags field is defined as follows:</t>
<figure anchor="LFLAGS" title="LFLAGS Bit Definition">
<artwork><![CDATA[ 0 1
0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+
|0|1|2|3| MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Where:<list hangIndent="15" style="hanging">
<t hangText="0 (Valid (V))">The Label value of the corresponding
SFL is valid. In an SFL Request setting the V Lflag indicates a
request for the specified label value. Where an SFL has a valid
flag clear in a request message this indicates that any SFL value
is acceptable.</t>
<t hangText="1 (Request (R))">Indicates to the Querier that this
member of the SFL batch is requested. Where a value is specified
in the request, but the Responder is unable honour that request,
no SFL is allocated and the corresponding A flag MUST be
cleared.</t>
<t hangText="2 (Allocated (A)">Indicates to the Querier that this
SFL was allocated.</t>
<t hangText="3 (Withdraw (W))">Indicates to the Responser that
this SFL is to be withdrawn and to the Querier that the withdrawal
has been carried out.</t>
<t hangText="MBZ">MUST be sent as zero and ignored on receive.</t>
</list></t>
<t>A flag value of one is true/set and a flag value of zero is
false/clear. The use of these bits is described in more detail in the
following sub-sections.</t>
</section>
<section title="SFL Control Proceedures">
<section title="Request/Grant">
<t>To request a batch of SFLs the Querier constructs an SFL Control
Request, encapsulates it in an SFL Control ACH and sends it to the
Responder via an appropriate path. It sets the Control Message Flag
to Query and the Control Code to Request. It chooses a session
identifier as a handle for this transaction and as a way of binding
this batch of SFLs to other operations that will use members of this
SFL batch. Since members of the batch are treated as a group, the
SFL Batch identifier is used to identify different SFL batches used
in conjunction with the same session identifier.</t>
<t>The requested lifetime is set. This is the number of seconds from
the time of the query to the time when the batch of SFLs will expire
unless refreshed.</t>
<t>The Num SFL field is set to the SFL batch size.</t>
<t>Each SFL is set as follows: if a specific value is requested (for
example for continuity across system restarts) this is written into
the SFV n field and the V LFlag set. Otherwise, and including spare
SFLs where an allocation is not requested, the label value is set to
zero and the V LFlag is cleared. For each SFL entry where an
allocation is requested the R LFlag is set. All other LFlags are
cleared.</t>
<t>The Forwarding Equivalence Class (FEC) is set to the FEC for
which the SFLs are requested.</t>
<t>The Message Length is determined and filled in.</t>
<t>The Responder proceeds as follows:</t>
<t>It sets the control Message Flag to Response and initially sets
the Control Code to Grant.</t>
<t>For each SFL with an R flag set, it determines whether it can
honour the request, if so sets the A Lflag, and if the SFL value in
the query was zero it overwrites it with the allocated SFL label
value. In all other cases it leaves the SFL value and LFlag
unchanged.</t>
<t>The lifetime field is updated with the lifetime of the SFLs if
this is different from the requested lifetime.</t>
<t>All other fields in the Query message are left unchanged and the
message is sent back to the Querier using the signaled or previously
agreed message path.</t>
<t>Where the offered lifetime is other than the requested lifetime
the Querier may accept the proposed value, or withdraw the SFLs and
attempt to negotiate a new set of SFLs with a different
lifetime.</t>
<t>If the Responder is unable to allocate all of the requested SFLs
it MUST respond with a response code of SFL-Unable. The Querier MUST
determine whether the allocated SFLs were adequate for its purposes
and MUST send a withdraw if there are not adequate. A Querier MUST
NOT attempt to hoard labels in the hope that the residual labels
needed may become available in the future.</t>
<t>A Querier MUST wait a configured time (suggested wait of 60
seconds) before reattempting negotiation for a resource. Any failure
to negotiate the required resources MUST be notified through the
management interface of both Querier and Responder.</t>
<t>A Querier MUST NOT send an expired SFL to a Responder since to do
so may invalidate another SFL operation.</t>
</section>
<section title="Refresh">
<t>To request the lifetime refresh of a batch of SFLs the Querier
constructs an SFL Refresh Request, encapsulates it in an SFL Control
ACH and sends it to the Responder via an appropriate path. It sets
the Control Message Flag to Query and the Control Code to Refresh.
It uses the session identifier and the SFL Batch identifier that it
used to request this SFL batch.</t>
<t>The requested lifetime is set. This is the number of seconds from
the time of the query to the time when the batch of SFLs will expire
unless refreshed.</t>
<t>The Num SFL field is set to the SFL batch size.</t>
<t>Each SFL is set as follows: the allocated SFL label value is
written into the SFL n field and the V LFlag set. All other LFlags
are cleared.</t>
<t>The Forwarding Equivalence Class (FEC) is set to the FEC for
which the SFLs are requested.</t>
<t>The Message Length is determined and filled in.</t>
<t>The Responder proceeds as follows:</t>
<t>It sets the control Message Flag to Response and sets the Control
Code to Refresh-Ack.</t>
<t>It sets the lifetime to the lifetime of the SFL.</t>
<t>All other fields in the Query message are left unchanged and the
message is sent back to the Querier using the signaled or previously
agreed message path.</t>
<t>Where the offered lifetime is other than the requested lifetime
the Querier may accept the proposed value, or withdraw the SFLs and
attempt to negotiate a new set of SFLs with a different
lifetime.</t>
<t>A Querier MUST wait a configured time (suggested wait of 60
seconds) before reattempting negotiation for a resource. Any failure
to negotiate the required resources MUST be notified through the
management interface of both Querier and Responder.</t>
</section>
<section title="Withdraw">
<t>To request the withdrawal of some or all of a batch of SFLs the
Querier constructs an SFL Withdraw Request, encapsulates it in an
SFL Control ACH and sends it to the Responder via an appropriate
path. It sets the Control Message Flag to Query and the Control Code
to Withdraw. It uses the session identifier and the SFL Batch
identifier that it used to request this SFL batch.</t>
<t>The requested lifetime is set to zero.</t>
<t>The Num SFL field is set to the SFL batch size.</t>
<t>Each SFL being withdrawn is set as follows: the allocated SFL
label value is written into the SFL n field and the V and W LFlags
set. All other LFlags are cleared.</t>
<t>The Forwarding Equivalence Class (FEC) is set to the FEC for
which the SFLs are requested.</t>
<t>The Message Length is determined and filled in.</t>
<t>The Responder proceeds as follows:</t>
<t>It sets the control Message Flag to Response and sets the Control
Code to Withdraw-Ack.</t>
<t>All other fields in the Query message are left unchanged and the
message is sent back to the Querier using the signaled or previously
agreed message path.</t>
<t>A Querier MUST wait a configured time (suggested wait of 60
seconds) before reattempting a Withdraw request. No more than three
Withdraw requests should be made.</t>
<t></t>
</section>
<section title="Timer Accuracy">
<t>The lifetime of SFLs is expected to be sufficiently long that
there are no significant constraints on timer accuracy. A node
should be conservative in its assumptions concerning the lifetime of
an SFL. A Querier MUST stop using a SFL significantly before the
expiry of its lifetime and a Responder must maintain an SFL in
active operation significantly beyond nominal expiry. A margin of
the order of minutes is RECOMMENDED.</t>
</section>
</section>
</section>
<section anchor="RPATH" title="Return Path">
<t>Where the LSP is a mulit-point to point, or multi-point to
multi-point MPLS LSP (or other MPLS construct) the RFC6374 Address TLV
MUST be included in Query packet, even if the response is requested
in-band, since this is needed to provide the necessary return address
for this request.</t>
<t></t>
</section>
<section title="Manageability Considerations">
<t>This may be provided in a future version of this memo.</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>It is assumed that this protocol is run in a well managed MPLS
network with strict access controls preventing unwanted parties from
generating MPLS OAM packets. The control protocol described in this memo
thus introduced no additional MPLS security vulnerabilities.</t>
</section>
<section title="IANA Considerations">
<t>As per the IANA considerations in <xref target="RFC5586"></xref>,
IANA is requested to allocate the following Channel Types in the "MPLS
Generalized Associated Channel (G-ACh) Types" registry:</t>
<figure>
<artwork><![CDATA[ Value Description TLV Follows Reference
------ ---------------------------------------- ----------- ---------
0x0XXX SFL Control No This]]></artwork>
</figure>
<t></t>
<t>A value of 0x60 is suggested.</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.RFC.5036'?>
<?rfc include='reference.RFC.5586'?>
</references>
</back>
</rfc>
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