One document matched: draft-xu-sfc-using-mpls-spring-03.xml
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<rfc category="info" docName="draft-xu-sfc-using-mpls-spring-03"
ipr="trust200902">
<front>
<title abbrev="">Service Function Chaining Using MPLS-SPRING</title>
<author fullname="Xiaohu Xu" initials="X.X." surname="Xu">
<organization>Huawei</organization>
<address>
<!--
<postal>
<street></street>
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<!--
<city>Soham</city>
<region></region>
<code></code>
<country>UK</country>
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<phone>+44 7889 488 335</phone>
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<email>xuxiaohu@huawei.com</email>
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</address>
</author>
<author fullname="Zhenbin Li" initials="Z.L." surname="Li">
<organization>Huawei</organization>
<address>
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<email>lizhenbin@huawei.com</email>
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</address>
</author>
<author fullname="Himanshu Shah" initials="H.S." surname="Shah">
<organization>Ciena</organization>
<address>
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<email>hshah@ciena.com</email>
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</author>
<author fullname="Luis M. Contreras" initials="L.M." surname="Contreras">
<organization>Telefonica I+D</organization>
<address>
<postal>
<street>Ronda de la Comunicacion, s/n</street>
<street>Sur-3 building, 3rd floor</street>
<city>Madrid,</city>
<code>28050</code>
<country>Spain</country>
</postal>
<email>luismiguel.contrerasmurillo@telefonica.com</email>
<uri>http://people.tid.es/LuisM.Contreras/</uri>
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<!--
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<date day="" month="" year="2015"/>
<abstract>
<t>Source Packet Routing in Networking (SPRING) WG specifies a special
source routing mechanism. Such source routing mechanism can be leveraged
to realize the service path layer functionality of the service function
chaining (i.e, steering traffic through a particular service function
path) by encoding the service function path or the service function
chain information as the explicit path information. This document
describes how to leverage the MPLS-based source routing mechanism as
developed by the SPRING WG to realize the service path layer
functionality of the service function chaining.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>When applying a particular Service Function Chain (SFC) <xref
target="I-D.ietf-sfc-architecture"/> to the traffic selected by a
service classifier, the traffic need to be steered through an ordered
set of Service Functions (SF) in the network. This ordered set of SFs in
the network indicates the Service Function Path (SFP) associated with
the above SFC. To steer the selected traffic through an ordered list of
SFs in the network, the traffic need to be attached by the service
classifier with the information about the SFP (i.e., specifying exactly
which Service Function Forwarders (SFFs) and which SFs are to be visited
by traffic), the SFC, or the partially specified SFP which is in between
the former two extremes. Source Packet Routing in Networking (SPRING) WG
specifies a special source routing mechanism which can be used to steer
traffic through an ordered set of routers (i.e., an explicit path). Such
source routing mechanism can be leveraged to realize the service path
layer functionality of the SFC (i.e., steering traffic through a
particular SFP) by encoding the SFP information as the explicit path
information contained in packets. The source routing mechanism specified
by the SPRING WG can be applied to the MPLS data plane <xref
target="I-D.ietf-spring-segment-routing-mpls"/>. This document describes
how to leverage the MPLS-based source routing mechanisms to realize the
service path layer functionality of the service function chaining. Note
that this approach is aligned with the Transport Derived SFF mode as
described in Section 4.3.1 of <xref
target="I-D.ietf-sfc-architecture"/>.</t>
<section title="Requirements Language">
<t>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 <xref
target="RFC2119">RFC 2119</xref>.</t>
</section>
</section>
<section anchor="Teminology" title="Terminology">
<t>This memo makes use of the terms defined in <xref
target="I-D.ietf-spring-segment-routing"/> and <xref
target="I-D.ietf-sfc-architecture"/>.</t>
</section>
<section anchor="Advertising" title="Solution Description">
<t><figure>
<artwork align="center"><![CDATA[ +----------------------------------------------- ----+
| SPRING Netowrks |
| +---------+ +---------+ |
| | SF1 | | SF2 | |
| +----+----+ +----+----+ |
| | | |
| (1) | (2) | (3) |
+----+-----+ ---> +----+----+ ----> +----+----+ ---> +---+---+
|Classifier+------+ SFF1 +-------+ SFF2 +-------+ D |
+----------+ +---------+ +---------+ +---+---+
| |
+----------------------------------------------------+
Figure 1: Service Function Chaining in SPRING Networks]]></artwork>
</figure></t>
<t>As shown in Figure 1, assume SFF1 and SFF2 are two MPLS-SPRING-
capable nodes. They are also Service Function Forwarders (SFF) to which
two SFs (i.e., SF1 and SF2) are attached respectively. In addition, they
have allocated and advertised Segment IDs (SID) for their locally
attached SFs. In the MPLS-SPRING context, SIDs are intercepted as MPLS
labels. For example, SFF1 allocates and advertises an SID (i.e.,
SID(SF1)) for SF1 while SFF2 allocates and advertises an SID ( i.e.,
SID(SF2)) for SF2. These SIDs which are used to indicate SFs are
referred to as SF SIDs. To encode the SFP information by an MPLS label
stack, those SF SIDs as mentioned above would be interpreted as local
MPLS labels. In addition, assume node SIDs for SFF1 and SFF2 are
SID(SFF1) and SID(SFF2) respectively. Now assume a given traffic flow
destined for destination D is selected by the service classifier to go
through a particular SFC (i.e., SF1-> SF2) before reaching its final
destination D. Section 3.1 describes how to leverage the MPLS- based
source routing mechanisms to realize the service path functionality of
the service function chaining (i.e., by encoding the SFP information
within an MPLS label stack). Section 3.2 describeds how to carry
metadata over MPLS packets.</t>
<section title="Encoding SFP Information by an MPLS Label Stack">
<t>Since the selected packet needs to travel through an SFC (i.e.,
SF1->SF2), the service classifier would attach a segment list of
(i.e., SID(SFF1)->SID(SF1)->SID(SFF2)-> SID(SF2)) which
indicates the corresponding SFP to the packet. This segment list is
actually represented by a MPLS label stack. When the encapsulated
packet arrives at SFF1, SFF1 would know which SF should be performed
according to the current top label (i.e., SID (SF1)) of the received
MPLS packet. Before sending the packet to SF1, the whole MPLS label
stack (i.e., SID(SFF2)->SID(SF2)) MUST be stripped. After receiving
the packet returned from SF1, SFF1 would reimpose the MPLS label stack
which had been stripped before to the packet and then send it to SFF2
according to the current top label (i.e., SID (SFF2) ). When the
encapsulated packet arrives at SFF2, SFF2 would do the similar action
as what has been done by SFF1. To some extent, the MPLS label stack
here could be looked as a specific implementation of the SFC
encapsulation used for containing the SFP information <xref
target="I-D.ietf-sfc-architecture"/>.</t>
<t>If there is no MPLS LSP towards the next node segment (i.e., the
next SFF identified by the current top label), the corresponding
IP-based tunnel (e.g., MPLS-in-IP/GRE tunnel <xref target="RFC4023"/>,
MPLS-in-L2TPv3 tunnel <xref target="RFC4817"/> or MPLS-in-UDP tunnel
<xref target="I-D.ietf-mpls-in-udp"/>) could be used instead (For more
details about this special usage, please refer to <xref
target="I-D.xu-spring-islands-connection-over-ip"/>). Since the
transport (i.e., the underlay) could be IPv4, IPv6 or even MPLS
networks, the above approach of encoding the SFP information by an
MPLS label stack is fully transport-independent which is one of the
major requirements for the SFC encapsulation <xref
target="I-D.ietf-sfc-architecture"/>.</t>
<t>In addition, the service classifier could further impose metadata
on the MPLS packet through the Network Service Header (NSH) <xref
target="I-D.quinn-sfc-nsh"/> (As for how to contain the NSH within a
MPLS packet, please see Section 3.3). Here the Service Path field
wihin the NSH would not be used for the path selection purpose anymore
and therefore it MUST be set to a particular value to indicate such
particular usage. In addition, the service index value within the NSH
is set to a value indicating the total number of SFs within the
service function path. The service index SHOULD be decreased by one on
each SF or SF-proxy on behalf of the corresponding legacy SF. When the
service index become zero, the NSH MUST be removed from the packet by
the SF or SF-proxy on behalf of the corresponding legacy SF. </t>
</section>
<section title="How to Contain Metadata within an MPLS Packet">
<t>Since the MPLS encapsulation has no explicit protocol identifier
field to indicate the protocol type of the MPLS payload, how to
indicate the presence of metadata (i.e., the NSH which is only used as
a metadata containner) in MPLS packets is a potential issue. There is
a possible ways to address the above issue: SFFs allocate two
different labels for a given SF, one indicates the presence of NSH
while the other indicates the absence of NSH. This approach has no
change to the current MPLS architecture but it would require more than
one label binding for a given SF. </t>
</section>
</section>
<!---->
<section anchor="Acknowledgements" title="Acknowledgements">
<t>The authors would like to thank Loa Andersson and Andrew G. Malis for
their valuable comments and suggestions on the draft. The authors would
like to thank Adrian Farrel, Stewart Bryant, Alexander Vainshtein, Joel
M. Halpern for their commnents on how to indicate the presence of
metadata within an MPLS packet.</t>
<!---->
</section>
<section anchor="IANA" title="IANA Considerations">
<t>TBD.</t>
<!---->
</section>
<section anchor="Security" title="Security Considerations">
<t>TBD</t>
<!---->
</section>
</middle>
<back>
<references title="Normative References">
&RFC2119;
<?rfc include="reference.I-D.ietf-spring-segment-routing-mpls"?>
<?rfc include="reference.I-D.ietf-sfc-architecture"?>
<!---->
</references>
<references title="Informative References">
<!---->
<?rfc include="reference.I-D.ietf-spring-segment-routing"?>
<?rfc include="reference.I-D.xu-spring-islands-connection-over-ip"?>
<?rfc include="reference.I-D.quinn-sfc-nsh"?>
<?rfc include="reference.RFC.4023"?>
<?rfc include="reference.RFC.4817"?>
<?rfc include="reference.I-D.ietf-mpls-in-udp"?>
</references>
</back>
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