Internet DRAFT - draft-malis-mpls-sfc-encapsulation
draft-malis-mpls-sfc-encapsulation
MPLS Working Group A. Malis
Internet-Draft S. Bryant
Intended status: Informational Huawei Technologies
Expires: April 14, 2019 J. Halpern
Ericsson
W. Henderickx
Nokia
October 11, 2018
MPLS Encapsulation for SFC NSH
draft-malis-mpls-sfc-encapsulation-03
Abstract
This document describes how to use a Service Function Forwarder (SFF)
Label (similar to a pseudowire label or VPN label) to indicate the
presence of a Service Function Chaining (SFC) Network Service Header
(NSH) between an MPLS label stack and the packet payload. This
allows SFC packets using the NSH to be forwarded between SFFs over an
MPLS network, and the selection between multiple SFFs in the
destination MPLS node.
Status of This Memo
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This Internet-Draft will expire on April 14, 2019.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. MPLS Encapsulation Using an SFF Label . . . . . . . . . . . . 3
2.1. MPLS Label Stack Construction at the Sending Node . . . . 3
2.2. SFF Label Processing at the Destination Node . . . . . . 4
3. Equal Cost Multipath (ECMP) Considerations . . . . . . . . . 4
4. Operations, Administration, and Maintenance (OAM)
Considerations . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
As discussed in [RFC8300], a number of transport encapsulations for
the Service Function Chaining (SFC) Network Service Header (NSH)
already exist, such as Ethernet, GRE [RFC2784], and VXLAN-GPE
[I-D.ietf-nvo3-vxlan-gpe].
This document describes an MPLS transport encapsulation for the NSH,
and also describes how to use a Service Function Forwarder (SFF)
[RFC7665] Label to indicate the presence of the NSH in the MPLS
packet payload. This allows SFC packets using the NSH to be
forwarded between SFFs in an MPLS transport network, where MPLS is
used to interconnect the network nodes that contain one or more SFFs.
The label is also used to select between multiple SFFs in the
destination MPLS node.
SFF Labels are similar to other service labels at the bottom of an
MPLS label stack that denote the contents of the MPLS payload being
other than IP, such as a layer 2 pseudowire, an IP packet that is
routed in a VPN context with a private address, or an Ethernet
virtual private wire service.
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This informational document follows well-established MPLS procedures
and does not require any actions by IANA or any new protocol
extensions.
2. MPLS Encapsulation Using an SFF Label
The encapsulation is a standard MPLS label stack [RFC3032] with an
SFF Label at the bottom of the stack, followed by a NSH as defined by
[RFC8300] and the NSH payload.
Much like a pseudowire label, an SFF Label is allocated by the
downstream receiver of the NSH from its per-platform label space.
If a receiving node supports more than one SFF (i.e, more than one
SFC forwarding instance), then the SFF Label can be used to select
the proper SFF, by having the receiving node advertise more than one
SFF Label to its upstream sending nodes as appropriate.
The method used by the downstream receiving node to advertise SFF
Labels to the upstream sending node is out of scope of this document.
That said, a number of methods are possible, such as via a protocol
exchange, or via a controller that manages both the sender and the
receiver using NETCONF/YANG, BGP, PCEP, etc. These are meant as
possible examples and not to constrain the future definition of such
advertisement methods.
While the SFF label will usually be at the bottom of the label stack,
there may be cases where there are additional label stack entries
beneath it. For example, when an ACH is carried that applies to the
SFF, a GAL [RFC5586] will be in the label stack below the SFF.
Similarly, an ELI/EL [RFC6790] may be carried below the SFF in the
label stack. This is identical to the situation with VPN labels.
2.1. MPLS Label Stack Construction at the Sending Node
When one SFF wishes to send an SFC packet with the NSH to another SFF
over an MPLS transport network, a label stack needs to be constructed
by the MPLS node that contains the sending SFF in order to transport
the packet to the destination MPLS node that contains the receiving
SFF. The label can be constructed as follows:
1. Push on zero or more labels that are interpreted by the
destination MPLS node, such as the Generic Associated Channel
[RFC5586] label (see OAM Considerations below).
2. Push on the SFF Label to identify the desired SFF in the
receiving MPLS node.
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3. Push on zero or more additional labels such that (a) the
resulting label stack will cause the packet to be transported to
the destination MPLS node, and (b) when the packet arrives at the
destination node, either:
* the SFF Label will be at the top of the label stack, or
* the SFF Label will rise to the top of the label stack before
the packet is forwarded to another node and before the packet
is dispatched to a higher layer.
2.2. SFF Label Processing at the Destination Node
The destination MPLS node performs a lookup on the SFF label to
retrieve the next-hop context between the SFF and SF, e.g. to
retrieve the destination MAC address in the case where native
Ethernet encapsulation is used between SFF and SF. How the next-hop
context is populated is out of the scope of this document.
The receiving MPLS node then pops the SFF Label (and any labels
beneath it) so that the destination SFF receives the SFC packet with
the NSH is at the top of the packet.
3. Equal Cost Multipath (ECMP) Considerations
As discussed in [RFC4928] and [RFC7325], there are ECMP
considerations for payloads carried by MPLS.
Many existing routers use deep packet inspection to examine the
payload of an MPLS packet, and if the first nibble of the payload is
equal to 0x4 or 0x6, these routers (sometimes incorrectly, as
discussed in [RFC4928]) assume that the payload is IPv4 or IPv6
respectively, and as a result, perform ECMP load balancing based on
(presumed) information present in IP/TCP/UDP payload headers or in a
combination of MPLS label stack and (presumed) IP/TCP/UDP payload
headers in the packet.
For SFC, ECMP may or may not be desirable. To prevent unintended
ECMP when it is not desired, the NSH Base Header was carefully
constructed so that the NSH could not look like IPv4 or IPv6 based on
its first nibble. See Section 2.2 of [RFC8300] for further details.
If ECMP is desired when SFC is used with an MPLS transport network,
there are two possible options, Entropy [RFC6790] and Flow-Aware
Transport [RFC6391] labels. A recommendation between these options,
and their proper placement in the label stack, is for future study.
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4. Operations, Administration, and Maintenance (OAM) Considerations
OAM at the SFC Layer is handled by SFC-defined mechanisms [RFC8300].
However, OAM may be required at the MPLS transport layer. If so,
then standard MPLS-layer OAM mechanisms such as the Generic
Associated Channel [RFC5586] label may be used.
5. IANA Considerations
This document does not request any actions from IANA.
Editorial note to RFC Editor: This section may be removed at your
discretion.
6. Security Considerations
This document describes a method for transporting SFC packets using
the NSH over an MPLS transport network. It follows well-established
MPLS procedures and does not define any new protocol elements or
allocate any new code points. It is therefore operationally
equivalent to other existing SFC transport encapsulations as defined
in [RFC8300]. As such, it should have no effect on SFC security as
already discussed in Section 8 of [RFC8300].
7. Acknowledgements
The authors would like to thank Jim Guichard, Eric Rosen, Med
Boucadair, Sasha Vainshtein, and Jeff Tantsura for their reviews and
comments.
8. References
8.1. Normative References
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
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8.2. Informative References
[I-D.ietf-nvo3-vxlan-gpe]
Maino, F., Kreeger, L., and U. Elzur, "Generic Protocol
Extension for VXLAN", draft-ietf-nvo3-vxlan-gpe-06 (work
in progress), April 2018.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
DOI 10.17487/RFC2784, March 2000,
<https://www.rfc-editor.org/info/rfc2784>.
[RFC4928] Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal
Cost Multipath Treatment in MPLS Networks", BCP 128,
RFC 4928, DOI 10.17487/RFC4928, June 2007,
<https://www.rfc-editor.org/info/rfc4928>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/info/rfc5586>.
[RFC6391] Bryant, S., Ed., Filsfils, C., Drafz, U., Kompella, V.,
Regan, J., and S. Amante, "Flow-Aware Transport of
Pseudowires over an MPLS Packet Switched Network",
RFC 6391, DOI 10.17487/RFC6391, November 2011,
<https://www.rfc-editor.org/info/rfc6391>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[RFC7325] Villamizar, C., Ed., Kompella, K., Amante, S., Malis, A.,
and C. Pignataro, "MPLS Forwarding Compliance and
Performance Requirements", RFC 7325, DOI 10.17487/RFC7325,
August 2014, <https://www.rfc-editor.org/info/rfc7325>.
[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>.
Authors' Addresses
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Andrew G. Malis
Huawei Technologies
Email: agmalis@gmail.com
Stewart Bryant
Huawei Technologies
Email: stewart.bryant@gmail.com
Joel M. Halpern
Ericsson
Email: joel.halpern@ericsson.com
Wim Henderickx
Nokia
Email: wim.henderickx@nokia.com
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